29 C.F.R. § 1630.3 : Labor — REGULATIONS RELATING TO LABOR — EQUAL EMPLOYMENT OPPORTUNITY COMMISSION — REGULATIONS TO IMPLEMENT THE EQUAL EMPLOYMENT PROVISIONS OF THE AMERICANS WITH DISABILITIES ACT — Exceptions to the definitions of ''Disability'' and ''Qualified Individual with a Disability.''

(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.
(b) However, the terms disability and qualified individual with a disability may not exclude an individual who:
(1) Has successfully completed a supervised drug rehabilitation program and is no longer engaging in the illegal use of drugs, or has otherwise been rehabilitated successfully and is no longer engaging in the illegal use of drugs; or
(2) Is participating in a supervised rehabilitation program and is no longer engaging in such use; or
(3) Is erroneously regarded as engaging in such use, but is not engaging in such use.
(c) It shall not be a violation of this part for a covered entity to adopt or administer reasonable policies or procedures, including but not limited to drug testing, designed to ensure that an individual described in paragraph (b) (1) or (2) of this section is no longer engaging in the illegal use of drugs. (See § 1630.16 Drug testing).
(d) Disability does not include:
(1) Transvestism, transsexualism, pedophilia, exhibitionism, voyeurism, gender identity disorders not resulting from physical impairments, or other sexual behavior disorders;
(2) Compulsive gambling, kleptomania, or pyromania; or
(3) Psychoactive substance use disorders resulting from current illegal use of drugs.
(e) Homosexuality and bisexuality are not impairments and so are not disabilities as defined in this part.

29 C.F.R. §1630.3