The ADA (Title I) restricts when and how employers can require medical examinations. Pre-offer: no medical exams or disability-related questions allowed. Post-offer/pre-employment: medical exams are permitted if required of all entering employees in that job category. Current employees: medical exams must be job-related and consistent with business necessity. The ADA also requires reasonable accommodations for qualified individuals with disabilities unless it causes undue hardship. Drug testing is generally not considered a "medical examination" under the ADA, and current illegal drug use is not a protected disability.