29 CFR Part 1630, Regulations to Implement the Equal Employment Provisions of the ADA (Title I Regulations with amendments issued through May 2016)

(a) The terms disability and qualified individual with a disability do not include individuals currently engaging in the illegal use of drugs, when the covered entity acts on the basis of such use.

(1) Drug means a controlled substance, as defined in schedules I through V of section 202 of the Controlled Substances Act (21 U.S.C 812).

(2) Illegal use of drugs means the use of drugs the possession or distribution of which is unlawful under the Controlled Substances Act, as periodically updated by the Food and Drug Administration. This term does not include the use of a drug taken under the supervision of a licensed health care professional, or other uses authorized by the Controlled Substances Act or other provisions of Federal law.