People that use drugs or are addicted to drugs are not protected under the ADA. 42 U.S.C. § 12114(a). Tests for drug usage can be conducted at any time during the employment process. The ADA does not exclude—
42 U.S.C. § 12114(b).
The ADA protects recovering addicts from discrimination on the basis of their status as an addict and a reasonable accommodation for an addict may include time off for treatment.
Addiction to alcohol is considered a disability, however under the ADA alcoholics are held to the same job performance standards as all other employees which includes not drinking on the job.
Tests for drug use are not considered medical examinations under the ADA and therefore not a prohibited pre-employment medical examination. 42 U.S.C. § 12114(d). People using drugs illegally are not protected under the ADA and may be denied employment on the basis of a positive drug test.
For additional information about drug testing, see Governmental Employee Drug Testing-The Constitutional Issues.