Opinion of the Court

NOTICE: This opinion is subject to formal revision before publication in thepreliminary print of the United States Reports. Readers are requested tonotify the Reporter of Decisions, Supreme Court of the United States, Wash ington, D. C. 20543, of any typographical or other formal errors, in orderthat corrections may be made before the preliminary print goes to press.


No. 04–623



[January 17, 2006]


JUSTICE KENNEDY delivered the opinion of the Court.

The question before us is whether the Controlled Sub stances Act allows the United States Attorney General to prohibit doctors from prescribing regulated drugs for use in physician-assisted suicide, notwithstanding a state law permitting the procedure. As the Court has observed, “Americans are engaged in an earnest and profound de bate about the morality, legality, and practicality of physi cian-assisted suicide.” Washington v. Glucksberg, 521

U. S. 702, 735 (1997). The dispute before us is in part a product of this political and moral debate, but its resolu tion requires an inquiry familiar to the courts: interpret ing a federal statute to determine whether Executiveaction is authorized by, or otherwise consistent with, the enactment.

In 1994, Oregon became the first State to legalize as sisted suicide when voters approved a ballot measureenacting the Oregon Death With Dignity Act (ODWDA).Ore. Rev. Stat. §127.800 et seq. (2003). ODWDA, whichsurvived a 1997 ballot measure seeking its repeal, ex empts from civil or criminal liability state-licensed physi

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cians who, in compliance with the specific safeguards in ODWDA, dispense or prescribe a lethal dose of drugs uponthe request of a terminally ill patient.

The drugs Oregon physicians prescribe under ODWDAare regulated under a federal statute, the Controlled Substances Act (CSA or Act). 84 Stat. 1242, as amended, 21 U. S. C. §801 et seq. The CSA allows these particulardrugs to be available only by a written prescription from a registered physician. In the ordinary course the samedrugs are prescribed in smaller doses for pain alleviation.

A November 9, 2001 Interpretive Rule issued by theAttorney General addresses the implementation and enforcement of the CSA with respect to ODWDA. It de termines that using controlled substances to assist suicide is not a legitimate medical practice and that dispensing or prescribing them for this purpose is unlawful under theCSA. The Interpretive Rule’s validity under the CSA is the issue before us.


We turn first to the text and structure of the CSA. Enacted in 1970 with the main objectives of combating drug abuse and controlling the legitimate and illegitimate traffic in controlled substances, the CSA creates a com prehensive, closed regulatory regime criminalizing the unauthorized manufacture, distribution, dispensing, andpossession of substances classified in any of the Act’s fiveschedules. Gonzales v. Raich, 545 U. S. ____, ___ (2005) (slip op., at 9–10); 21 U. S. C. §841 (2000 ed. and Supp. II); 21 U. S. C. §844. The Act places substances in one of fiveschedules based on their potential for abuse or depend ence, their accepted medical use, and their accepted safetyfor use under medical supervision. Schedule I contains the most severe restrictions on access and use, and Sched ule V the least. Raich, supra, at ___ (slip op., at 11); 21

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U. S. C. §812. Congress classified a host of substances when it enacted the CSA, but the statute permits the Attorney General to add, remove, or reschedule sub stances. He may do so, however, only after making par ticular findings, and on scientific and medical matters heis required to accept the findings of the Secretary of Health and Human Services (Secretary). These proceed ings must be on the record after an opportunity for com ment. See 21 U. S. C. A. §811 (main ed. and Supp. 2005).

The present dispute involves controlled substances listed in Schedule II, substances generally available onlypursuant to a written, nonrefillable prescription by a physician. 21 U. S. C. §829(a). A 1971 regulation promul gated by the Attorney General requires that every pre scription for a controlled substance “be issued for a legiti mate medical purpose by an individual practitioner actingin the usual course of his professional practice.” 21 CFR §1306.04(a) (2005).

To prevent diversion of controlled substances with medi cal uses, the CSA regulates the activity of physicians. To issue lawful prescriptions of Schedule II drugs, physiciansmust “obtain from the Attorney General a registration issued in accordance with the rules and regulations prom ulgated by him.” 21 U. S. C. §822(a)(2). The Attorney General may deny, suspend, or revoke this registration if, as relevant here, the physician’s registration would be“inconsistent with the public interest.” §824(a)(4); §822(a)(2). When deciding whether a practitioner’s regis tration is in the public interest, the Attorney General “shall” consider:

“(1) The recommendation of the appropriate Statelicensing board or professional disciplinary authority.

“(2) The applicant’s experience in dispensing, or conducting research with respect to controlledsubstances.

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“(3) The applicant’s conviction record under Federal or State laws relating to the manufacture, distribu tion, or dispensing of controlled substances.

“(4) Compliance with applicable State, Federal, or local laws relating to controlled substances.“(5) Such other conduct which may threaten the public health and safety.” §823(f).

The CSA explicitly contemplates a role for the States inregulating controlled substances, as evidenced by its pre emption provision.

“No provision of this subchapter shall be construed as indicating an intent on the part of the Congress to occupy the field in which that provision operates . . . to the exclusion of any State law on the same subjectmatter which would otherwise be within the authorityof the State, unless there is a positive conflict between that provision . . . and that State law so that the twocannot consistently stand together.” §903.

B Oregon voters enacted ODWDA in 1994. For Oregonresidents to be eligible to request a prescription under ODWDA, they must receive a diagnosis from their attend ing physician that they have an incurable and irreversible disease that, within reasonable medical judgment, will cause death within six months. Ore. Rev. Stat. §§127.815, 127.800(12) (2003). Attending physicians must also de termine whether a patient has made a voluntary request, ensure a patient’s choice is informed, and refer patients tocounseling if they might be suffering from a psychological disorder or depression causing impaired judgment. §§127.815, 127.825. A second “consulting” physician must examine the patient and the medical record and confirmthe attending physician’s conclusions. §127.800(8). Ore gon physicians may dispense or issue a prescription for the

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requested drug, but may not administer it. §§127.815(L),


The reviewing physicians must keep detailed medicalrecords of the process leading to the final prescription,§127.855, records that Oregon’s Department of HumanServices reviews, §127.865. Physicians who dispensemedication pursuant to ODWDA must also be registered with both the State’s Board of Medical Examiners and the federal Drug Enforcement Administration (DEA). §127.815(1)(L). In 2004, 37 patients ended their lives byingesting a lethal dose of medication prescribed under ODWDA. Oregon Dept. of Human Servs., Seventh Annual Report on Oregon’s Death with Dignity Act 20 (Mar. 10, 2005).

C In 1997, Members of Congress concerned about ODWDA invited the DEA to prosecute or revoke the CSA registra tion of Oregon physicians who assist suicide. They con tended that hastening a patient’s death is not legitimatemedical practice, so prescribing controlled substances forthat purpose violates the CSA. Letter from Sen. Orrin Hatch and Rep. Henry Hyde to Thomas A. Constantine(July 25, 1997), reprinted in Hearings on S. 2151 before the Senate Committee on the Judiciary, 105th Cong., 2d Sess., 2–3 (1999) (hereinafter Hearings). The letter re ceived an initial, favorable response from the director ofthe DEA, see Letter from Thomas A. Constantine to Sen. Orrin Hatch (Nov. 5, 1997), Hearings 4–5, but Attorney General Reno considered the matter and concluded that the DEA could not take the proposed action because the CSA did not authorize it to “displace the states as theprimary regulators of the medical profession, or to over ride a state’s determination as to what constitutes legiti mate medical practice,” Letter from Attorney GeneralJanet Reno to Sen. Orrin Hatch, on Oregon’s Death with

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Dignity Act (June 5, 1998), Hearings 5–6. Legislation wasthen introduced to grant the explicit authority AttorneyGeneral Reno found lacking; but it failed to pass. See

H. R. 4006, 105th Cong., 2d Sess. (1998); H. R. 2260, 106thCong., 1st Sess. (1999).

In 2001, John Ashcroft was appointed Attorney General. Perhaps because Mr. Ashcroft had supported efforts tocurtail assisted suicide while serving as a Senator, see, e.g., 143 Cong. Rec. 5589–5590 (1997) (remarks of Sen.Ashcroft), Oregon Attorney General Hardy Myers wrotehim to request a meeting with Department of Justice officials should the Department decide to revisit the appli cation of the CSA to assisted suicide. Letter of Feb. 2, 2001, App. to Brief for Patient-Respondents in Opposition55a. Attorney General Myers received a reply letter fromone of Attorney General Ashcroft’s advisers writing on his behalf, which stated

“I am aware of no pending legislation in Congressthat would prompt a review of the Department’s in terpretation of the CSA as it relates to physician-assisted suicide. Should such a review be commenced in the future, we would be happy to include yourviews in that review.” Letter from Lori Sharpe (Apr. 17, 2001), id., at 58a.

On November 9, 2001, without consulting Oregon orapparently anyone outside his Department, the AttorneyGeneral issued an Interpretive Rule announcing his intent to restrict the use of controlled substances for physician-assisted suicide. Incorporating the legal analysis of a memorandum he had solicited from his Office of Legal Counsel, the Attorney General ruled

“assisting suicide is not a ‘legitimate medical purpose’ within the meaning of 21 CFR 1306.04 (2001), and that prescribing, dispensing, or administering feder ally controlled substances to assist suicide violates the

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Controlled Substances Act. Such conduct by a physi cian registered to dispense controlled substances may‘render his registration . . . inconsistent with the pub lic interest’ and therefore subject to possible suspen sion or revocation under 21 U. S. C. 824(a)(4). The At torney General’s conclusion applies regardless ofwhether state law authorizes or permits such conductby practitioners or others and regardless of the condi tion of the person whose suicide is assisted.” 66 Fed. Reg. 56608 (2001).

There is little dispute that the Interpretive Rule wouldsubstantially disrupt the ODWDA regime. Respondentscontend, and petitioners do not dispute, that every pre scription filled under ODWDA has specified drugs classi fied under Schedule II. A physician cannot prescribe the substances without DEA registration, and revocation orsuspension of the registration would be a severe restric tion on medical practice. Dispensing controlled substanceswithout a valid prescription, furthermore, is a federal crime. See, e.g., 21 U. S. C. §841(a)(1) (2000 ed., Supp. II); United States v. Moore, 423 U. S. 122 (1975).

In response the State of Oregon, joined by a physician, a pharmacist, and some terminally ill patients, all fromOregon, challenged the Interpretive Rule in federal court. The United States District Court for the District of Oregon entered a permanent injunction against the InterpretiveRule’s enforcement.

A divided panel of the Court of Appeals for the Ninth Circuit granted the petitions for review and held the In terpretive Rule invalid. Oregon v. Ashcroft, 368 F. 3d 1118 (2004). It reasoned that, by making a medical procedureauthorized under Oregon law a federal offense, the Inter pretive Rule altered the “‘“usual constitutional balance between the States and the Federal Government”’” with out the requisite clear statement that the CSA authorized

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such action. Id., at 1124–1125 (quoting Gregory v. Ashcroft, 501 U. S. 452, 460 (1991) (in turn quoting Atas cadero State Hospital v. Scanlon, 473 U. S. 234, 242 (1985))). The Court of Appeals held in the alternative that the Interpretive Rule could not be squared with the plain language of the CSA, which targets only conventional drug abuse and excludes the Attorney General from decisions on medical policy. 368 F. 3d, at 1125–1129.

We granted the Government’s petition for certiorari.543 U. S. 1145 (2005).

II Executive actors often must interpret the enactmentsCongress has charged them with enforcing and imple menting. The parties before us are in sharp disagreement both as to the degree of deference we must accord the Interpretive Rule’s substantive conclusions and whether the Rule is authorized by the statutory text at all. Al though balancing the necessary respect for an agency’sknowledge, expertise, and constitutional office with the courts’ role as interpreter of laws can be a delicate matter, familiar principles guide us. An administrative rule may receive substantial deference if it interprets the issuingagency’s own ambiguous regulation. Auer v. Robbins, 519

U. S. 452, 461–463 (1997). An interpretation of an am biguous statute may also receive substantial deference. Chevron U. S. A. Inc. v. Natural Resources Defense Coun cil, Inc., 467 U. S. 837, 842–845 (1984). Deference in accordance with Chevron, however, is warranted only “when it appears that Congress delegated authority to the agency generally to make rules carrying the force of law,and that the agency interpretation claiming deference was promulgated in the exercise of that authority.” United States v. Mead Corp., 533 U. S. 218, 226–227 (2001). Otherwise, the interpretation is “entitled to respect” onlyto the extent it has the “power to persuade.” Skidmore v.

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Swift & Co., 323 U. S. 134, 140 (1944).

A The Government first argues that the Interpretive Rule is an elaboration of one of the Attorney General’s ownregulations, 21 CFR §1306.04 (2005), which requires allprescriptions be issued “for a legitimate medical purpose by an individual practitioner acting in the usual course of his professional practice.” As such, the Government says,the Interpretive Rule is entitled to considerable deference in accordance with Auer. In our view Auer and the standard of deference it ac cords to an agency are inapplicable here. Auer involved a disputed interpretation of the Fair Labor Standards Act of 1938 as applied to a class of law enforcement officers. Under regulations promulgated by the Secretary of Labor, an exemption from overtime pay depended, in part, onwhether the employees met the “salary basis” test. 519

U. S., at 454–455. In this Court the Secretary of Labor filed an amicus brief explaining why, in his view, theregulations gave exempt status to the officers. Id., at 461. We gave weight to that interpretation, holding that be cause the applicable test was “a creature of the Secretary’sown regulations, his interpretation of it is, under ourjurisprudence, controlling unless plainly erroneous or inconsistent with the regulation.” Ibid. (internal quota tion marks omitted).

In Auer, the underlying regulations gave specificity to astatutory scheme the Secretary was charged with enforc ing and reflected the considerable experience and exper tise the Department of Labor had acquired over time withrespect to the complexities of the Fair Labor StandardsAct. Here, on the other hand, the underlying regulationdoes little more than restate the terms of the statute itself. The language the Interpretive Rule addresses comes from Congress, not the Attorney General, and the near

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equivalence of the statute and regulation belies the Gov ernment’s argument for Auer deference.

The Government does not suggest that its interpretationturns on any difference between the statutory and regula tory language. The CSA allows prescription of drugs onlyif they have a “currently accepted medical use,” 21 U. S. C.§812(b); requires a “medical purpose” for dispensing theleast controlled substances of those on the schedules, §829(c); and, in its reporting provision, defines a “validprescription” as one “issued for a legitimate medical pur pose,” §830(b)(3)(A)(ii). Similarly, physicians are consid ered to be acting as practitioners under the statute if they dispense controlled substances “in the course of profes sional practice.” §802(21). The regulation uses the terms“legitimate medical purpose” and “the course of profes sional practice,” ibid., but this just repeats two statutory phrases and attempts to summarize the others. It giveslittle or no instruction on a central issue in this case: Who decides whether a particular activity is in “the course ofprofessional practice” or done for a “legitimate medical purpose”? Since the regulation gives no indication how todecide this issue, the Attorney General’s effort to decide itnow cannot be considered an interpretation of the regula tion. Simply put, the existence of a parroting regulationdoes not change the fact that the question here is not the meaning of the regulation but the meaning of the statute.An agency does not acquire special authority to interpret its own words when, instead of using its expertise and experience to formulate a regulation, it has elected merely to paraphrase the statutory language.

Furthermore, as explained below, if there is statutory authority to issue the Interpretive Rule it comes from the 1984 amendments to the CSA that gave the AttorneyGeneral authority to register and deregister physiciansbased on the public interest. The regulation was enactedbefore those amendments, so the Interpretive Rule cannot be justified as indicative of some intent the AttorneyGeneral had in 1971. That the current interpretation runscounter to the “intent at the time of the regulation’s prom ulgation,” is an additional reason why Auer deference is unwarranted. Thomas Jefferson Univ. v. Shalala, 512

U. S. 504, 512 (1994) (internal quotation marks omitted). Deference under Auer being inappropriate, we turn to thequestion whether the Interpretive Rule, on its own terms, is a permissible interpretation of the CSA.

B Just as the Interpretive Rule receives no deferenceunder Auer, neither does it receive deference under Chev ron. If a statute is ambiguous, judicial review of adminis trative rulemaking often demands Chevron deference; and the rule is judged accordingly. All would agree, we shouldthink, that the statutory phrase “legitimate medical pur pose” is a generality, susceptible to more precise definitionand open to varying constructions, and thus ambiguous inthe relevant sense. Chevron deference, however, is not accorded merely because the statute is ambiguous and anadministrative official is involved. To begin with, the rulemust be promulgated pursuant to authority Congress has delegated to the official. Mead, 533 U. S., at 226–227. The Attorney General has rulemaking power to fulfill his duties under the CSA. The specific respects in whichhe is authorized to make rules, however, instruct us that he is not authorized to make a rule declaring illegitimate a medical standard for care and treatment of patients thatis specifically authorized under state law. The starting point for this inquiry is, of course, thelanguage of the delegation provision itself. In many cases authority is clear because the statute gives an agency broad power to enforce all provisions of the statute. See, e.g., National Cable & Telecommunications Assn. v. Brand X Internet Services, 545 U. S. ___, ___ (2005) (slip op., at 8)

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(explaining that a Federal Communications Commission regulation received Chevron deference because “Congress has delegated to the Commission the authority to . . . ‘prescribe such rules and regulations as may be necessary in the public interest to carry out the provisions’ of the Act” (quoting 47 U. S. C. §201(b))); Household Credit Services, Inc. v. Pfennig, 541 U. S. 232, 238 (2004) (giving Chevron deference to a Federal Reserve Board regulationwhere “Congress has expressly delegated to the Board the authority to prescribe regulations . . . as, in the judgmentof the Board, ‘are necessary or proper to effectuate the purposes of’” the statute (quoting 15 U. S. C. §1604(a))).The CSA does not grant the Attorney General this broad authority to promulgate rules.

The CSA gives the Attorney General limited powers, tobe exercised in specific ways. His rulemaking authority under the CSA is described in two provisions: (1) “TheAttorney General is authorized to promulgate rules andregulations and to charge reasonable fees relating to the registration and control of the manufacture, distribution,and dispensing of controlled substances and to listedchemicals,” 21 U. S. C. A. §821 (Supp. 2005); and (2) “TheAttorney General may promulgate and enforce any rules, regulations, and procedures which he may deem necessaryand appropriate for the efficient execution of his functionsunder this subchapter,” 21 U. S. C. §871(b). As is evident from these sections, Congress did not delegate to theAttorney General authority to carry out or effect all provi sions of the CSA. Rather, he can promulgate rules relat ing only to “registration” and “control,” and “for the effi cient execution of his functions” under the statute.

Turning first to the Attorney General’s authority tomake regulations for the “control” of drugs, this delegation cannot sustain the Interpretive Rule’s attempt to definestandards of medical practice. Control is a term of art in the CSA. “As used in this subchapter,” §802––the sub

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chapter that includes §821––

“The term ‘control’ means to add a drug or other sub

stance, or immediate precursor, to a schedule under

part B of this subchapter, whether by transfer from

another schedule or otherwise.” §802(5).

To exercise his scheduling power, the Attorney General must follow a detailed set of procedures, including re questing a scientific and medical evaluation from the Secretary. See 21 U. S. C. A. §§811, 812 (main ed. and Supp. 2005). The statute is also specific as to the manner in which the Attorney General must exercise this author ity: “Rules of the Attorney General under this subsection[regarding scheduling] shall be made on the record afteropportunity for a hearing pursuant to the rulemakingprocedures prescribed by [the Administrative ProcedureAct, 5 U. S. C. §553].” 21 U. S. C. §811(a). The Interpre tive Rule now under consideration does not concern the scheduling of substances and was not issued after the required procedures for rules regarding scheduling, soit cannot fall under the Attorney General’s “control” authority.

Even if “control” in §821 were understood to signifysomething other than its statutory definition, it would not support the Interpretive Rule. The statutory references to“control” outside the scheduling context make clear thatthe Attorney General can establish controls “against diversion,” e.g., §823(a)(1), but do not give him authority todefine diversion based on his view of legitimate medical practice. As explained below, the CSA’s express limita tions on the Attorney General’s authority, and other indi cations from the statutory scheme, belie any notion that the Attorney General has been granted this implicit au thority. Indeed, if “control” were given the expansivemeaning required to sustain the Interpretive Rule, itwould transform the carefully described limits on the

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Attorney General’s authority over registration and sched uling into mere suggestions.

We turn, next, to the registration provisions of the CSA.Before 1984, the Attorney General was required to regis ter any physician who was authorized by his State. The Attorney General could only deregister a physician whofalsified his application, was convicted of a felony relating to controlled substances, or had his state license or regis tration revoked. See 84 Stat. 1255. The CSA was amended in 1984 to allow the Attorney General to deny registration to an applicant “if he determines that theissuance of such registration would be inconsistent withthe public interest.” 21 U. S. C. §823(f). Registration mayalso be revoked or suspended by the Attorney General on the same grounds. §824(a)(4). In determining consistency with the public interest, the Attorney General must, asdiscussed above, consider five factors, including: the State’s recommendation; compliance with state, federal, and local laws regarding controlled substances; and public health and safety. §823(f).

The Interpretive Rule cannot be justified under this part of the statute. It does not undertake the five-factor analy sis and concerns much more than registration. Nor does the Interpretive Rule on its face purport to be an applica tion of the registration provision in §823(f). It is, instead, an interpretation of the substantive federal law require ments (under 21 CFR §1306.04 (2005)) for a valid pre scription. It begins by announcing that assisting suicide isnot a “legitimate medical purpose” under §1306.04, and that dispensing controlled substances to assist a suicideviolates the CSA. 66 Fed. Reg. 56608 (2001). Violation is a criminal offense, and often a felony, under 21 U. S. C. §841 (2000 ed. and Supp. II). The Interpretive Rule thuspurports to declare that using controlled substances for physician-assisted suicide is a crime, an authority thatgoes well beyond the Attorney General’s statutory power

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to register or deregister.

The Attorney General’s deregistration power, of course,may carry implications for criminal enforcement because ifa physician dispenses a controlled substance after he is deregistered, he violates §841. The Interpretive Ruleworks in the opposite direction, however: it declares cer tain conduct criminal, placing in jeopardy the registrationof any physician who engages in that conduct. To the extent the Interpretive Rule concerns registration, itsimply states the obvious because one of the five factors the Attorney General must consider in deciding the “public interest” is “[c]ompliance with applicable State, Federal,or local laws relating to controlled substances.” 21 U. S. C. §823(f)(4). The problem with the design of the Interpre tive Rule is that it cannot, and does not, explain why the Attorney General has the authority to decide what consti tutes an underlying violation of the CSA in the first place.The explanation the Government seems to advance is that the Attorney General’s authority to decide whether aphysician’s actions are inconsistent with the “public inter est” provides the basis for the Interpretive Rule.

By this logic, however, the Attorney General claimsextraordinary authority. If the Attorney General’s argu ment were correct, his power to deregister necessarily would include the greater power to criminalize even the actions of registered physicians, whenever they engage inconduct he deems illegitimate. This power to criminal ize—unlike his power over registration, which must beexercised only after considering five express statutory factors—would be unrestrained. It would be anomalous for Congress to have so painstakingly described the Attor ney General’s limited authority to deregister a singlephysician or schedule a single drug, but to have given him, just by implication, authority to declare an entire class of activity outside “the course of professional practice,” andtherefore a criminal violation of the CSA. See Federal

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Maritime Comm’n v. Seatrain Lines, Inc., 411 U. S. 726, 744 (1973) (“In light of these specific grants of . . . author ity, we are unwilling to construe the ambiguous provisions. . . to serve this purpose [of creating further authority]—apurpose for which it obviously was not intended”).

Sutton v. United Air Lines, Inc., 527 U. S. 471 (1999), isinstructive. The statute at issue was the Americans with Disabilities Act of 1990 (ADA), which, like the CSA, di vides interpretive authority among various Executive actors. The Court relied on “the terms and structure of the ADA” to decide that neither the Equal Employment Opportunity Commission, nor any other agency had au thority to define “disability” in the ADA. Id., at 479. Specifically, the delegating provision stated that theEEOC “shall issue regulations . . . to carry out this sub chapter,” 42 U. S. C. §12116, and the section of the statutedefining “disability” was in a different subchapter. The Court did not accept the idea that because “the employ ment subchapter, i.e., ‘this subchapter,’ includes otherprovisions that use the defined terms, . . . [t]he EEOC might elaborate, through regulations, on the meaning of‘disability’ . . . if elaboration is needed in order to ‘carry out’ the substantive provisions of ‘this subchapter.’” 527

U. S., at 514 (BREYER, J., dissenting). See also Adams Fruit Co. v. Barrett, 494 U. S. 638, 649–650 (1990) (hold ing that a delegation of authority to promulgate motorvehicle safety “standards” did not include the authority todecide the pre-emptive scope of the federal statute because “[n]o such delegation regarding [the statute’s] enforcementprovisions is evident in the statute”).

The same principle controls here. It is not enough thatthe terms “public interest,” “public health and safety,” and “Federal law” are used in the part of the statute over which the Attorney General has authority. The statutory terms “public interest” and “public health” do not call on the Attorney General, or any other Executive official, to

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make an independent assessment of the meaning of fed eral law. The Attorney General did not base the Interpre tive Rule on an application of the five-factor test generally,or the “public health and safety” factor specifically. Even if he had, it is doubtful the Attorney General could cite the“public interest” or “public health” to deregister a physi cian simply because he deemed a controversial practicepermitted by state law to have an illegitimate medical purpose.

As for the federal law factor, though it does require theAttorney General to decide “[c]ompliance” with the law, itdoes not suggest that he may decide what the law says. Were it otherwise, the Attorney General could authorita tively interpret “State” and “local laws,” which are alsoincluded in 21 U. S. C. §823(f), despite the obvious consti tutional problems in his doing so. Just as he must evalu ate compliance with federal law in deciding about registra tion, the Attorney General must as surely evaluate compliance with federal law in deciding whether to prose cute; but this does not entitle him to Chevron deference. See Crandon v. United States, 494 U. S. 152, 177 (1990) (SCALIA, J., concurring in judgment) (“The Justice De partment, of course, has a very specific responsibility todetermine for itself what this statute means, in order to decide when to prosecute; but we have never thought that the interpretation of those charged with prosecutingcriminal statutes is entitled to deference”).

The limits on the Attorney General’s authority to definemedical standards for the care and treatment of patientsbear also on the proper interpretation of §871(b). This section allows the Attorney General to best determine howto execute “his functions.” It is quite a different matter,however, to say that the Attorney General can define the substantive standards of medical practice as part of hisauthority. To find a delegation of this extent in §871would put that part of the statute in considerable tension

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with the narrowly defined delegation concerning control and registration. It would go, moreover, against the plainlanguage of the text to treat a delegation for the “execu tion” of his functions as a further delegation to define other functions well beyond the statute’s specific grants of authority. When Congress chooses to delegate a power of this extent, it does so not by referring back to the adminis trator’s functions but by giving authority over the provi sions of the statute he is to interpret. See, e.g., National Cable & Telecommunications Assn., 545 U. S. ___; House hold Credit Services, 541 U. S. 232.

The authority desired by the Government is inconsistentwith the design of the statute in other fundamental re spects. The Attorney General does not have the sole dele gated authority under the CSA. He must instead share it with, and in some respects defer to, the Secretary, whose functions are likewise delineated and confined by the statute. The CSA allocates decisionmaking powers among statutory actors so that medical judgments, if they are tobe decided at the federal level and for the limited objects of the statute, are placed in the hands of the Secretary. In the scheduling context, for example, the Secretary’s rec ommendations on scientific and medical matters bind the Attorney General. The Attorney General cannot control asubstance if the Secretary disagrees. 21 U. S. C. §811(b). See H. R. Rep. No. 91–1444, pt. 1, p. 33 (1970) (the section“is not intended to authorize the Attorney General to undertake or support medical and scientific research [for the purpose of scheduling], which is within the competenceof the Department of Health, Education, and Welfare”).

In a similar vein the 1970 Act’s regulation of medicalpractice with respect to drug rehabilitation gives the Attorney General a limited role; for it is the Secretarywho, after consultation with the Attorney General andnational medical groups, “determine[s] the appropriatemethods of professional practice in the medical treatment

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of . . . narcotic addiction.” 42 U. S. C. §290bb–2a; see 21

U. S. C. §823(g) (2000 ed. and Supp. II) (stating that the Attorney General shall register practitioners who dispensedrugs for narcotics treatment when the Secretary hasdetermined the applicant is qualified to treat addicts andthe Attorney General has concluded the applicant willcomply with record keeping and security regulations); Moore, 423 U. S., at 144 (noting that in enacting the addic tion-treatment provisions, Congress sought to change the fact “that ‘criminal prosecutions’ in the past had turned on the opinions of federal prosecutors”); H. R. Rep. No. 93–884, p. 6 (1974) (“This section preserves the distinctions found in the [CSA] between the functions of the AttorneyGeneral and the Secretary . . . . All decisions of a medical nature are to be made by the Secretary . . . . Law en forcement decisions respecting the security of stocks ofnarcotics drugs and the maintenance of records on suchdrugs are to be made by the Attorney General”).

Post enactment congressional commentary on the CSA’sregulation of medical practice is also at odds with theAttorney General’s claimed authority to determine appro priate medical standards. In 1978, in preparation for ratification of the Convention on Psychotropic Substances,Feb. 21, 1971, [1979–1980] 32 U. S. T. 543, T. I. A. S. No. 9725, Congress decided it would implement the UnitedStates’ compliance through “the framework of the proce dures and criteria for classification of substances providedin the” CSA. 21 U. S. C. §801a(3). It did so to ensure that “nothing in the Convention will interfere with ethical medical practice in this country as determined by [the Secretary] on the basis of a consensus of the views of the American medical and scientific community.” Ibid.

The structure of the CSA, then, conveys unwillingness to cede medical judgments to an Executive official wholacks medical expertise. In interpreting statutes that divide authority, the Court has recognized: “Because

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historical familiarity and policymaking expertise account in the first instance for the presumption that Congressdelegates interpretive lawmaking power to the agencyrather than to the reviewing court, we presume here that Congress intended to invest interpretive power in theadministrative actor in the best position to develop theseattributes.” Martin v. Occupational Safety and Health Review Comm’n, 499 U. S. 144, 153 (1991) (citations omit ted). This presumption works against a conclusion that the Attorney General has authority to make quintessen tially medical judgments.

The Government contends the Attorney General’s deci sion here is a legal, not a medical, one. This generality, however, does not suffice. The Attorney General’s Inter pretive Rule, and the Office of Legal Counsel memo itincorporates, place extensive reliance on medical judg ments and the views of the medical community in conclud ing that assisted suicide is not a “legitimate medical pur pose.” See 66 Fed. Reg. 56608 (noting the “medical” distinctions between assisting suicide and giving sufficientmedication to alleviate pain); Memorandum from Office of Legal Counsel to Attorney General (June 27, 2001), App. to Pet. for Cert. 121a–122a, and n. 17 (discussing the“Federal medical policy” against physician-assisted sui cide), id., at 124a–130a (examining views of the medicalcommunity). This confirms that the authority claimed bythe Attorney General is both beyond his expertise andincongruous with the statutory purposes and design.

The idea that Congress gave the Attorney General suchbroad and unusual authority through an implicit delega tion in the CSA’s registration provision is not sustainable. “Congress, we have held, does not alter the fundamental details of a regulatory scheme in vague terms or ancillary provisions—it does not, one might say, hide elephants in mouseholes.” Whitman v. American Trucking Assns., Inc.,531 U. S. 457, 468 (2001); see FDA v. Brown & Williamson

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Tobacco Corp., 529 U. S. 120, 160 (2000) (“[W]e are confi dent that Congress could not have intended to delegate a decision of such economic and political significance to an agency in so cryptic a fashion”).

The importance of the issue of physician-assisted sui cide, which has been the subject of an “earnest and pro found debate” across the country, Glucksberg, 521 U. S., at 735, makes the oblique form of the claimed delegation allthe more suspect. Under the Government’s theory, more over, the medical judgments the Attorney General couldmake are not limited to physician-assisted suicide. Were this argument accepted, he could decide whether anyparticular drug may be used for any particular purpose, or indeed whether a physician who administers any contro versial treatment could be deregistered. This would occur, under the Government’s view, despite the statute’s ex press limitation of the Attorney General’s authority toregistration and control, with attendant restrictions oneach of those functions, and despite the statutory purposes to combat drug abuse and prevent illicit drug trafficking.

We need not decide whether Chevron deference would be warranted for an interpretation issued by the Attorney General concerning matters closer to his role under the CSA, namely preventing doctors from engaging in illicitdrug trafficking. In light of the foregoing, however, theCSA does not give the Attorney General authority to issue the Interpretive Rule as a statement with the force of law.

If, in the course of exercising his authority, the AttorneyGeneral uses his analysis in the Interpretive Rule only for guidance in deciding when to prosecute or deregister, then the question remains whether his substantive interpreta tion is correct. Since the Interpretive Rule was not prom ulgated pursuant to the Attorney General’s authority, itsinterpretation of “legitimate medical purpose” does notreceive Chevron deference. Instead, it receives deference only in accordance with Skidmore. “The weight of such a

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judgment in a particular case will depend upon the thor oughness evident in its consideration, the validity of itsreasoning, its consistency with earlier and later pro nouncements, and all those factors which give it power to persuade, if lacking power to control.” 323 U. S., at 140; see also Mead, 533 U. S., at 235 (noting that an opinion receiving Skidmore deference may “claim the merit of itswriter’s thoroughness, logic, and expertness, its fit withprior interpretations, and any other sources of weight”). The deference here is tempered by the Attorney General’slack of expertise in this area and the apparent absence ofany consultation with anyone outside the Department ofJustice who might aid in a reasoned judgment. In any event, under Skidmore, we follow an agency’s rule only to the extent it is persuasive, see Christensen v. Harris County, 529 U. S. 576, 587 (2000); and for the reasons givenand for further reasons set out below, we do not find the Attorney General’s opinion persuasive.

III As we have noted before, the CSA “repealed most of theearlier antidrug laws in favor of a comprehensive regimeto combat the international and interstate traffic in illicit drugs.” Raich, 545 U. S., at ___ (slip op., at 9). In doingso, Congress sought to “conquer drug abuse and to controlthe legitimate and illegitimate traffic in controlled sub stances.” Ibid. It comes as little surprise, then, that we have not considered the extent to which the CSA regulatesmedical practice beyond prohibiting a doctor from actingas a drug “‘pusher’” instead of a physician. Moore, 423

U. S., at 143. In Moore, we addressed a situation in which a doctor “sold drugs, not for legitimate purposes, butprimarily for the profits to be derived therefrom.” Id., at 135 (quoting H. R. Rep. No. 91–1444, pt. 1, at 10; internalquotation marks omitted). There the defendant, who had engaged in large-scale overprescribing of methadone,

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“concede[d] in his brief that he did not observe generally accepted medical practices.” 423 U. S., at 126. And in United States v. Oakland Cannabis Buyers’ Cooperative,532 U. S. 483 (2001), Congress’ express determination that marijuana had no accepted medical use foreclosed any argument about statutory coverage of drugs available by a doctor’s prescription.

In deciding whether the CSA can be read as prohibiting physician-assisted suicide, we look to the statute’s textand design. The statute and our case law amply support the conclusion that Congress regulates medical practiceinsofar as it bars doctors from using their prescription-writing powers as a means to engage in illicit drug dealing and trafficking as conventionally understood. Beyondthis, however, the statute manifests no intent to regulate the practice of medicine generally. The silence is under standable given the structure and limitations of federal ism, which allow the States “‘great latitude under theirpolice powers to legislate as to the protection of the lives, limbs, health, comfort, and quiet of all persons.’” Med tronic, Inc. v. Lohr, 518 U. S. 470, 475 (1996) (quoting Met ropolitan Life Ins. Co. v. Massachusetts, 471 U. S. 724, 756 (1985)).

The structure and operation of the CSA presume and rely upon a functioning medical profession regulatedunder the States’ police powers. The Attorney Generalcan register a physician to dispense controlled substances “if the applicant is authorized to dispense . . . controlledsubstances under the laws of the State in which he prac tices.” 21 U. S. C. §823(f). When considering whether torevoke a physician’s registration, the Attorney General looks not just to violations of federal drug laws; but he“shall” also consider “[t]he recommendation of the appro priate state licensing board or professional disciplinary authority” and the registrant’s compliance with state and local drug laws. Ibid. The very definition of a “practitio

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ner” eligible to prescribe includes physicians “licensed,registered, or otherwise permitted, by the United States orthe jurisdiction in which he practices” to dispense con trolled substances. §802(21). Further cautioning against the conclusion that the CSA effectively displaces theStates’ general regulation of medical practice is the Act’spre-emption provision, which indicates that, absent apositive conflict, none of the Act’s provisions should be“construed as indicating an intent on the part of the Con gress to occupy the field in which that provision operates . . . to the exclusion of any State law on the same subject matter which would otherwise be within the authority ofthe State.” §903.

Oregon’s regime is an example of the state regulation of medical practice that the CSA presupposes. Rather than simply decriminalizing assisted suicide, ODWDA limits itsexercise to the attending physicians of terminally ill pa tients, physicians who must be licensed by Oregon’s Board of Medical Examiners. Ore. Rev. Stat. §§127.815, 127.800(10) (2003). The statute gives attending physi cians a central role, requiring them to provide prognosesand prescriptions, give information about palliative alter natives and counseling, and ensure patients are competentand acting voluntarily. §127.815. Any eligible patientmust also get a second opinion from another registered physician, §127.820, and the statute’s safeguards requirephysicians to keep and submit to inspection detailed re cords of their actions, §§127.855, 127.865.

Even though regulation of health and safety is “primar ily, and historically, a matter of local concern,” Hillsbor ough County v. Automated Medical Laboratories, Inc., 471

U. S. 707, 719 (1985), there is no question that the FederalGovernment can set uniform national standards in these areas. See Raich, supra, at ___ (slip op., at 6). In connec tion to the CSA, however, we find only one area in whichCongress set general, uniform standards of medical prac

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tice. Title I of the Comprehensive Drug Abuse Prevention and Control Act of 1970, of which the CSA was Title II, provides that

“[The Secretary], after consultation with the AttorneyGeneral and with national organizations representa tive of persons with knowledge and experience in thetreatment of narcotic addicts, shall determine the ap propriate methods of professional practice in the medical treatment of the narcotic addiction of various classes of narcotic addicts, and shall report thereonfrom time to time to the Congress.” §4, 84 Stat. 1241, codified at 42 U. S. C. §290bb–2a.

This provision strengthens the understanding of the CSAas a statute combating recreational drug abuse, and also indicates that when Congress wants to regulate medical practice in the given scheme, it does so by explicit lan guage in the statute.

In the face of the CSA’s silence on the practice of medi cine generally and its recognition of state regulation of the medical profession it is difficult to defend the AttorneyGeneral’s declaration that the statute impliedly criminal izes physician-assisted suicide. This difficulty is com pounded by the CSA’s consistent delegation of medical judgments to the Secretary and its otherwise careful allocation of powers for enforcing the limited objects of the CSA. See Part II–B, supra. The Government’s attempt tomeet this challenge rests, for the most part, on the CSA’srequirement that every Schedule II drug be dispensedpursuant to a “written prescription of a practitioner.” 21

U. S. C. §829(a). A prescription, the Government argues, necessarily implies that the substance is being madeavailable to a patient for a legitimate medical purpose.The statute, in this view, requires an anterior judgmentabout the term “medical” or “medicine.” The Government contends ordinary usage of these words ineluctably refers

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to a healing or curative art, which by these terms cannot embrace the intentional hastening of a patient’s death. It also points to the teachings of Hippocrates, the positions ofprominent medical organizations, the Federal Government,and the judgment of the 49 States that have not legalized physician-assisted suicide as further support for the propo sition that the practice is not legitimate medicine. See Brief for Petitioners 22–24; Memorandum from Office of LegalCounsel to Attorney General, App. to Pet. for Cert. 124a–130a.

On its own, this understanding of medicine’s boundaries is at least reasonable. The primary problem with the Government’s argument, however, is its assumption thatthe CSA impliedly authorizes an Executive officer to bar ause simply because it may be inconsistent with one rea sonable understanding of medical practice. Viewed alone, the prescription requirement may support such an under standing, but statutes “should not be read as a series of unrelated and isolated provisions.” Gustafson v. Alloyd Co., 513 U. S. 561, 570 (1995). The CSA’s substantive provisions and their arrangement undermine this as- sertion of an expansive federal authority to regulatemedicine.

The statutory criteria for deciding what substances arecontrolled, determinations which are central to the Act, consistently connect the undefined term “drug abuse” with addiction or abnormal effects on the nervous system. When the Attorney General schedules drugs, he must consider a substance’s psychic or physiological dependenceliability. 21 U. S. C. §811(c)(7). To classify a substance inSchedules II through V, the Attorney General must find abuse of the drug leads to psychological or physical de pendence. §812(b). Indeed, the differentiation of Sched ules II through V turns in large part on a substance’s habit-forming potential: The more addictive a substance, the stricter the controls. Ibid. When Congress wanted to

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extend the CSA’s regulation to substances not obviouslyhabit forming or psychotropic, moreover, it relied not on Executive ingenuity, but rather on specific legislation. See §1902(a) of the Anabolic Steroids Control Act of 1990, 104Stat. 4851 (placing anabolic steroids in Schedule III).

The statutory scheme with which the CSA is inter twined further confirms a more limited understanding ofthe prescription requirement. When the Secretary consid ers FDA approval of a substance with “stimulant, depres sant, or hallucinogenic effect,” he must forward the infor mation to the Attorney General for possible scheduling. Shedding light on Congress’ understanding of drug abuse, this requirement appears under the heading “Abuse po tential.” 21 U. S. C. §811(f). Similarly, when Congressprepared to implement the Convention on Psychotropic Substances, it did so through the CSA. §801a.

The Interpretive Rule rests on a reading of the prescrip tion requirement that is persuasive only to the extent one scrutinizes the provision without the illumination of the rest of the statute. See Massachusetts v. Morash, 490

U. S. 107, 114–115 (1989). Viewed in its context, the prescription requirement is better understood as a provi sion that ensures patients use controlled substances under the supervision of a doctor so as to prevent addiction andrecreational abuse. As a corollary, the provision also bars doctors from peddling to patients who crave the drugs for those prohibited uses. See Moore, 423 U. S., at 135, 143. To read prescriptions for assisted suicide as constituting“drug abuse” under the CSA is discordant with the phrase’s consistent use throughout the statute, not to mention its ordinary meaning.

The Government’s interpretation of the prescriptionrequirement also fails under the objection that the AttorneyGeneral is an unlikely recipient of such broad authority, given the Secretary’s primacy in shaping medical policy under the CSA, and the statute’s otherwise careful alloca

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tion of decisionmaking powers. Just as the conventions of expression indicate that Congress is unlikely to alter a statute’s obvious scope and division of authority throughmuffled hints, the background principles of our federal system also belie the notion that Congress would use suchan obscure grant of authority to regulate areas tradition ally supervised by the States’ police power. It is unneces sary even to consider the application of clear statement requirements, see, e.g., United States v. Bass, 404 U. S. 336, 349 (1971); cf. BFP v. Resolution Trust Corporation, 511

U. S. 531, 544–546 (1994), or presumptions against pre emption, see, e.g., Rush Prudential HMO, Inc. v. Moran, 536

U. S. 355, 387 (2002), to reach this commonsense conclusion. For all these reasons, we conclude the CSA’s prescriptionrequirement does not authorize the Attorney General tobar dispensing controlled substances for assisted suicide in the face of a state medical regime permitting suchconduct.

IV The Government, in the end, maintains that the pre scription requirement delegates to a single Executiveofficer the power to effect a radical shift of authority fromthe States to the Federal Government to define generalstandards of medical practice in every locality. The text and structure of the CSA show that Congress did not have this far-reaching intent to alter the federal-state balanceand the congressional role in maintaining it. The judgment of the Court of Appeals is