21 U.S.C. § 956 — Exemption authority

Subject to paragraph (2), the Attorney General may by regulation exempt from sections 952(a) and (b), 953, 954, and 955 of this title any individual who has a controlled substance (except a substance in schedule I) in his possession for his personal medical use, or for administration to an animal accompanying him, if he lawfully obtained such substance and he makes such declaration (or gives such other notification) as the Attorney General may by regulation require.

Notwithstanding any exemption under paragraph (1), a United States resident who enters the United States through an international land border with a controlled substance (except a substance in schedule I) for which the individual does not possess a valid prescription issued by a practitioner (as defined in section 802 of this title) in accordance with applicable Federal and State law (or documentation that verifies the issuance of such a prescription to that individual) may not import^* the controlled substance into the United States in an amount that exceeds 50 dosage units of the controlled substance.