The Americans with Disabilities Act of 1990 (ADA) prohibits discrimination against a qualified individual with a disability in employment, public service, public accommodations, telecommunications, and transportation. The law requires an employer to provide reasonable accommodations that would allow an employee with a disability to perform the essential functions of the job. Under the ADA, a "disability" is defined as (1) a physical or mental impairment that substantially limits one or more of the major life activities of an individual, (2) a record of such an impairment, or (3) being regarded as having such an impairment. The definition of disability specifically excludes the current illegal use of drugs, including the unlawful use of legally obtained prescription drugs. There are as well numerous limits on those who can be classified as disabled. A "qualified person with a disability" is one who, with or without reasonable accommodation, can perform the essential functions of the job. A job function is "essential" if the purpose of the job is to perform that function. An employer is required to provide reasonable accommodations to assist a disabled person in doing a job unless such an accommodation creates an undue hardship for the employer. What constitutes an undue hardship is evaluated on a case by case basis and may be different for each job. The protections afforded under the ADA complement those rights that are accorded under Section 504 of the Rehabilitation Act of 1973.