21 U.S.C. § 956 — Exemption authority

(a) Individual possessing a controlled substance.
(1) Subject to paragraph (2), the Attorney General may by regulation exempt an individual from sections 952(a) and (b), 953, 954, and 955 if the individual possesses a controlled substance, other than a schedule I substance, for personal medical use or to give to an accompanying animal. The individual must have obtained it lawfully and must make the declaration or other notification that the Attorney General's regulations require.
(2) Regardless of an exemption under paragraph (1), a United States resident entering through an international land border with a controlled substance, other than a schedule I substance, may not import^* more than 50 dosage units into the United States if the resident lacks a valid prescription from a practitioner, as section 802 defines that term, issued under applicable Federal and State law, or documentation verifying that the prescription was issued to that resident.

(b) Compound, mixture, or preparation. The Attorney General may by regulation exempt a compound, mixture, or preparation containing a depressant or stimulant listed in schedule III paragraph (a) or (b), or in schedule IV or V, from all or part of this subchapter if:
(1) It contains one or more active medicinal ingredients that do not depress or stimulate the central nervous system; and
(2) Those ingredients are included in combinations, amounts, proportions, or concentrations that remove the potential for abuse of the ingredients that do depress or stimulate the central nervous system. This section does not define “depressant,” “stimulant,” “dosage units,” or “potential for abuse.”