Yes. A test for the illegal use of drugs is not considered a medical examination under the ADA; therefore, employers may conduct such testing of applicants or employees and make employment decisions based on the results. The ADA does not encourage, prohibit, or authorize drug tests.
If the results of a drug test reveal the presence of a lawfully prescribed drug or other medical information, such information must be treated as a confidential medical record.
For additional information, take a look at the following resources:
Fact Sheet: The ADA, Addiction, and Recovery