delivered the opinion of the Court.
The question presented in this case is whether the Federal Food, Drug, and Cosmetic Act precludes terminally ill cancer patients from obtaining Laetrile, a drug not recognized as “safe and effective” within the meaning of §201 (p) (1) of the Act, 52 Stat. 1041, as amended, 21 U. S. C. § 321 (p) (1).
I
Section 505 of the Federal Food, Drug, and Cosmetic Act, 52 Stat. 1052, as amended, 21 U. S. C. § 355, prohibits interstate distribution of any “new drug” unless the Secretary of Health, Education, and Welfare approves an application supported by substantial evidence of the drug’s safety and effectiveness. 1 As defined in § 201 (p) (1) of the Act, 21 TJ. S. C. § 321 (p) (1), the term “new drug” includes
“[a]ny drug . . . not generally recognized, among expertsqualified by scientific training and experience to evaluate the safety and effectiveness of drugs, as safe and effective for use under the conditions prescribed, recommended, or suggested in the labeling . . .
In 1975, terminally ill cancer patients and their spouses brought this action to enjoin the Government from interfering with the interstate shipment and sale of Laetrile, a drug not approved for distribution under the Act.
4
Finding that Laetrile, in proper dosages, was nontoxic and effective, the District Court ordered the Government to permit limited purchases of the drug by one of the named plaintiffs. 399 F.
After completion of administrative hearings,
6
the Commissioner issued his opinion on July 29, 1977. 42 Fed. Reg. 39768 (1977). He determined first that no uniform definition of Laetrile exists; rather, the term has been used generically for chemical compounds similar to, or consisting at least in part of, amygdalin, a glucoside present in the kernels or seeds of most fruits.
Id.,
at 39770-39772. The Commissioner further found that Laetrile in its various forms constituted a “new drug” as defined in § 201 (p)(l) of the Act because it was not generally recognized among experts as safe and effective for its prescribed use. See 42 Fed. Reg. 39775-39787 (1977). In so ruling, the Commissioner applied the statutory criteria delineated in
Weinberger
v.
Hynson, Westcott & Dunning, Inc.,
On review of the Commissioner’s decision, the District Court sustained his determination that Laetrile, because not generally regarded as safe or effective, constituted a new drug under §201(p)(l).
The Court of Appeals addressed neither the statutory nor the constitutional rulings of the District Court. Rather, the
We granted certiorari,
II
The Federal Food, Drug, and Cosmetic Act makes no special provision for drugs used to treat terminally ill patients. By its terms, § 505 of the Act requires premarketing approval for “any new drug” unless it is intended solely for investigative use or is exempt under one of the Act’s grandfather provisions. See nn. 2, 3, supra. And § 201 (p)(l) defines “new drug” to encompass “[a]ny drug .. . not generally recognized ... as safe and effective for use under the conditions prescribed, recommended, or suggested in the labeling.” See supra, at 546-547.
When construing a statute so explicit in scope, a court must act within certain well-defined constraints. If a legislative purpose is expressed in “plain and unambiguous language, . . . the . . . duty of the courts is to give it effect according to its terms.”
United States
v.
Lexington Mill & Elevator Co.,
A
Nothing in the history of the 1938
Food,
Drug, and Cosmetic Act, which first established procedures for review of drug safety, or of the 1962 Amendments, which added the current safety and effectiveness standards in §201 (p)(l),
8
suggests that Congress intended protection only for persons suffering from curable diseases. To the contrary, in deliberations preceding the 1938 Act, Congress expressed concern that individuals with fatal illnesses, such as cancer, should be shielded from fraudulent cures. See,
e. g.,
79 Cong. Rec. 5023 (1935) (remarks of Sen. Copeland, sponsor of the Act); 83 Cong. Rec. 7786-7787, 7789 (1938) (remarks of Reps. Phillips and Lea). Similarly, proponents of the 1962 Amendments to the Act, including Senator Kefauver, one of the bill’s sponsors,
In implementing the statutory scheme, the FDA has never made exception for drugs used by the terminally ill. As this Court has often recognized, the construction of a statute by those charged with its administration is entitled to substantial deference.
Board of Governors of FRS
v.
First Lincoln-
B
In the Court of Appeals’ view, an implied exemption from the Act was justified because the safety and effectiveness
A drug is effective within the meaning of §201 (p) (1) if there is general recognition among experts, founded on substantial evidence, that the drug in fact produces the results claimed for it under prescribed conditions. See
Weinberger
v.
Hynson, Westcott & Dunning, Inc.,
So too, the concept of safety under §201(p)(l) is not without meaning for terminal patients. New if any drugs are completely safe in the sense that they may be taken by all persons in all circumstances without risk.
11
Thus, the Commissioner generally considers a drug safe when the expected therapeutic gain justifies the risk entailed by its use.
12
For
Moreover, there is a special sense in which the relationship between drug effectiveness and safety has meaning in the context of incurable illnesses. An otherwise harmless drug can be dangerous to any patient if it does not produce its purported therapeutic effect. See 107 Cong. Rec. 5640 (1961) (comments of Sen. Kefauver). But if an individual suffering from a potentially fatal disease rejects conventional therapy in favor of a drug with no demonstrable curative properties, the consequences can be irreversible.
13
For this reason, even before the 1962 Amendments incorporated an efficacy standard into new drug application procedures, the FDA considered effectiveness when reviewing the safety of drugs used to treat terminal illness. See nn. 8, 9,
supra.
The FDA’s practice also reflects the recognition, amply supported by expert medical testimony in this case, that with diseases such as cancer it is often impossible to identify a patient as terminally ill except in retrospect.
14
Cancers vary considerably in behavior
It bears emphasis that although the Court of Appeals’ ruling was limited to Laetrile, its reasoning cannot be so readily confined. To accept the proposition that the safety and efficacy standards of the Act have no relevance for terminal patients is to deny the Commissioner’s authority over all drugs, how
We note finally that construing § 201 (p) (1) to encompass treatments for terminal diseases does not foreclose all resort to experimental cancer drugs by patients for whom conventional therapy is unavailing. Section 505 (i) of the Act, 21 U. S. C. § 355 (i), exempts from premarketing approval drugs intended solely for investigative use if they satisfy certain preclinical testing and other criteria.
17
An application for clinical testing of Laetrile by the National Cancer Institute is now pending before the Commissioner. Brief for United States
The judgment of the Court of Appeals is reversed, and the ease is remanded for further proceedings consistent with this opinion. 18
So ordered.
Notes
Section 505, as set forth in 21 U. S. C. §355, provides in part:
“(a) ... No person shall introduce or deliver for introduction into interstate commerce any new drug, unless an approval of an application filed pursuant to subsection (b) of this section is effective with respect to such drug.
“(b) . . . Any person may file with the Secretary an application with respect to any drug subject to the provisions of subsection (a) of this section. Such person shall submit to the Secretary as a part of the application (1) full reports of investigations which have been made to show whether or not such drug is safe for use and whether such drug is effective in use ....
“(d) ... If the Secretary finds . . . that (1) the investigations . . . required to be submitted to the Secretary ... do not include adequate tests by all methods reasonably applicable to show whether or not such drug is safe for use under the conditions prescribed, recommended, or suggested in the proposed labeling thereof; (2) the results of such tests show that such drug is unsafe for use under such conditions or do not show that such drug is safe for use under such conditions; ... (4) ... he has insufficient information to determine whether such drug is safe for use under such conditions; or (5) . . . there is a lack of substantial evidence that the drug will have the effect it purports or is represented to have under the conditions of use prescribed, recommended, or suggested in the proposed labeling thereof; or (6) based on a fair evaluation of all material facts, such labeling is false or misleading in any particular; he shall issue an order refusing to approve the application. ... As used in this subsection . . . , the term 'substantial evidence’ means evidence consisting of adequate and well-controlled investigations, including clinical investigations, by experts qualified by scientific training and experience to evaluate the effectiveness of the drug involved, on the basis of which it could fairly and responsibly be concluded by such experts that the drug will have the effect it purports or is represented to have under the conditions of use prescribed, recommended, or suggested in the labeling or proposed labeling thereof.
“(i) . . . The Secretary shall promulgate regulations for exempting from the operation of the foregoing subsections of this section drugs intended solely for investigational use by experts qualified by scientific training and experience to investigate the safety and effectiveness of drugs. . . .”
The Secretary has delegated his approval authority to the Commissioner of the Food and Drug Administration. See 21 CFR §5.1 (a)(1) (1978).
The requirements for investigative use are set forth in § 505 (i) of the Act, 21 U. S. C. § 355 (i). See n. 1, supra.
In the Federal Food, Drug, and Cosmetic Act of 1938, 52 Stat. 1041, Congress exempted from the definition of “new drug” any drug that was subject to the Pure Food and Drug Act of 1906, ch. 3915, 34 Stat. 768, if its labeling retained the same representations concerning conditions of use made prior to 1938. This exemption is currently contained in § 201 (p) (1) of the Act, as codified in 21 U. S. C. §321 (p) (1). The Drag Amendments of 1962 added a second grandfather clause, which provides:
“In the case of any drug which, on the day immediately preceding the enactment date [October 10, 1962], (A) was commercially used or sold in the United States, (B) was not a new drug as defined by section 201 (p) of the basic Act as then in force, and (C) was not covered by an effective [new drug] application under section 505 of that Act, the amendments to section 201 (p) made by this Act shall not apply to such drug when intended solely for use under conditions prescribed, recommended, or suggested in labeling with respect to such drug on that day.” § 107 (c)(4), 76 Stat. 789.
The suit was originally instituted by a cancer patient, Juanita Stowe, and her husband, Jimmie Stowe. After Ms. Stowe’s death, two other patients, Glen L. Rutherford and Phyllis S. Schneider, and Ms. Schneider’s husband, filed an amended complaint on behalf of a class composed of all cancer patients and spouses responsible for the costs of treatment. By order entered April 8, 1977, the District Court certified a class consisting of terminally ill cancer patients.
The District Court subsequently entered similar orders for other individuals who submitted affidavits averring their membership in the certified class of terminally EL cancer patients. See App. 1-6.
The Commissioner initiated proceedings with an announcement in the Federal Register seeking public comment. 42 Fed. Reg. 10066-10069 (1977). Notice was also afforded to certain known proponents of Laetrile. See id., at 39785-39786.
The Act does not define what constitutes general recognition of a drug’s safety and effectiveness under §201 (p)(l). However, based on the structure and purpose of the statutory scheme, this Court in
Wein-berger
v.
Hynson, Westcott & Dunning, Inc.,
Under the 1938 Act, a “new drag” was one not generally recognized by qualified experts as safe for its recommended use. §201 (p) (1), 52 Stat. 1041. The Drug Amendments of 1962, Pub. L. 87-781, 76 Stat. 789, redefined the term to include drugs not generally recognized as effective or safe for their intended use. §201 (p) (1), 21 U. S. C. §321 (p)(l). See swpra, at 546-547, 551. In addition, the Amendments provided that no new drug application may be approved absent substantial evidence that the drug is effective as well as safe under prescribed conditions. § 505 (d), 21 U. S. C. § 355 (d). See n. 1, supra.
The Senate Report states:
“The Food and Drug Administration now requires, in determining whether a 'new drug’ is safe, a showing as to the drug’s effectiveness where the drug is offered for use in the treatment of a life-threatening disease, or where it appears that the ‘new drug’ will occasionally produce serious toxic or even lethal effects so that only its usefulness would justify the risks involved in its use. In such cases, the determination of safety is, in the light of the purposes of the new drug provisions, considered by the Food and Drug Administration to be inseparable from consideration of the drug’s effectiveness. The provisions of the bill are in no way intended to affect any existing authority of the Department of Health, Education, and Welfare to consider and evaluate the effectiveness of a new drug in the context of passing upon its safety.” S. Rep. No. 1744, 87th Cong., 2d Sess., pt. 1, p. 15 (1962).
See also H. R. Rep. No. 2464, 87th Cong., 2d Sess., 3 (1962).
The FDA’s practice was further amplified by HEW Secretary Ribicoff in testimony on the bill that ultimately became the 1962 Amendments:
“If the drug is offered for treatment of progressive or life-threatening diseases, such as' cancer, ... we now consider its effectiveness. In such cases the determination of safety is, in the light of the purpose of the new drug provisions, inseparable from consideration of the drug’s effectiveness.” Hearings on S. 1552 before the Subcommittee on Antitrust and Monopoly of the Senate Committee on the Judiciary, 87th Cong., 1st Sess., 2588 (1961).
To be sure, it may not always be realistic to infer approval of a judicial or administrative interpretation from congressional silence alone. See,
e. g., Helvering
v.
Hallock,
The issue presented in this case plainly has not escaped public or legislative notice. Whether Laetrile should be freely accessible to cancer patients has been a frequent subject of political debate. Seventeen States have legalized the prescription and use of Laetrile for cancer treatment within their borders, and similar statutes have been defeated in 14 other States. See CCH F. D. Cosm. L. Rep. ¶ 42,292 (1978); Comment, Laetrile: Statutory and Constitutional Limitations on the Regulation of Ineffective Drugs, 127 U. Pa. L. Rev. 233, 234 n. 8 (1978). That Congress is aware of the FDA’s policy concerning Laetrile is evident from Senate Subcommittee hearings on the Commissioner’s 1977 ruling. See Hearing before the Subcommittee on Health and Scientific Research of the Senate Committee on Human Resources, 95th Cong., 1st Sess. (1977).
See L. Goodman & A. Gilman, The Pharmacological Basis of Therapeutics 325-339 (5th ed. 1975).
See statement of Dr. Theodore Klumpp, Chief, Drug Division, FDA, June 23, 1941, CCH F. D. Cosm. L. Rep. ¶ 71,053.59 (1977); n. 13, infra.
See, e. g., 42 Fed. Reg. 39768, 39787 (1977) (statement of Dr. Carl Leventhal, Deputy Director of - the Bureau of Drugs, FDA, and Assistant Professor of Neurology and Pathology at Georgetown University) (“The safety of a drug for human use depends, in large measure, on the therapeutic effectiveness of the particular drug. ... In the case of cancer, treatment with an ineffective drug will . . . inexorably lead to the patient’s death”); ibid, (statement of Dr. George J. Hill II, Chairman of the Department of Surgery at Marshall University School of Medicine, W. Ya.) (Ineffectual treatment can lead to delay in accepted modes of therapy and needless deaths; thus, “[i]n the absence of scientific evidence of effectiveness, no drug intended for use in treating cancer can be regarded as safe”).
See,
e. g., id.,
at 39805 (statement of Dr. Peter Wiemik, Chief of the
The Commissioner noted that these unexpected behavior patterns may account for anecdotal claims of Laetrile’s effectiveness. Users of Laetrile who experience spontaneous remissions or delayed responses to conventional therapy after its abandonment may ascribe their improvement to Laetrile without any objective basis for that attribution. See, e. g., id., at 39777 (statement of Dr. Daniel S. Martin, researcher in cancer immunology and chemotherapy); id., at 39800 (statement of Dr. Emil J. Frereich, Chief of the Division of Oncology at University of Texas Medical School at Houston); ibid, (statement of Dr. Melvin Krant, Director of Cancer Project at the University of Massachusetts Medical Center). Particularíy since accepted cancer treatments such as chemotherapy and radiation often have painful side effects, the Commissioner concluded that patients who subjectively perceive improvement after substituting Laetrile for these modes of therapy may erroneously believe that their condition has been arrested or ameliorated. See id., at 39777, 39799-39800.
CCH Fed. F. D. Cosm. L. Admin, Reps., 1907-1949, p. 745 (1951); id., at 1408; id., at 1170-1171, 1298-1299; id., at 224; FDA Ann. Reps., 1950-1974, pp. 309, 464; id., at 45; id., at 412.
See n. 1, supra. At present, some 300 experimental drugs are available to critically ill cancer patients at authorized institutions. See Brief for United States 34 n. 23; National Cancer Institute, Extramural Clinical Trial Programs of the Division of Cancer Treatment, General Overview and Scope of Contract-Supported Activities (1979). During 1977, over 90,000 cancer patients participated in investigative programs under the auspices of the National Cancer Institute or the Veterans’ Administration. Brief for United States 35 n. 23.
Respondents urge that we consider the District Court’s rulings on the constitutional and grandfather clause questions as alternative bases for sustaining the judgment below. However, since the Court of Appeals addressed neither issue, we remand the case for further consideration of respondents’ claims. See
Vermont Yankee Nuclear Power Corp.
v.
National Resources Defense Council, Inc.,
