They may be. While a current illegal user of drugs is not protected by the ADA if an employer acts on the basis of such use, a person who currently uses alcohol is not automatically denied protection. Alcoholism is an impairment, and if it substantially limits a major life activity (e.g., learning, concentrating, interacting with others, caring for oneself) it will constitute a disability. An alcoholic may be person with a disability and protected by the ADA if s/he is qualified to perform the essential functions of the job. An employer may be required to provide an accommodation to an alcoholic, (e.g. a flexible schedule to enable the employee to attend counseling appointments).
However, an employer can discipline, discharge or deny employment to an alcoholic whose use of alcohol adversely affects job performance or conduct. An employer also may prohibit the use of alcohol in the workplace and can require that employees not be under the influence of alcohol.
For additional information, take a look at the following resource:
Fact Sheet: The ADA, Addiction and Recovery