Adderall is a stimulant medication that's used to treat attention deficit-hyperactivity disorder (ADHD) and narcolepsy in adults and children. It contains the instant-release (IR) forms of dextroamphetamine and amphetamine salts. Adderall IR typically lasts 4-6 hours, while Adderall XR can last up to 12 hours. The half-life of Adderall, which influences how long it stays in a person's system, ranges from 9 to 14 hours, but this can vary based on individual factors such as urine pH and metabolic rate.