For people suffering from attention deficit hyperactivity disorder (ADHD) or narcolepsy, Dexedrine^® (dextroamphetamine sulfate) may help to treat their condition. When used in the proper doses to treat ADHD in children and teenagers, Dexedrine can cause a calming effect to help them focus and sit still. When Dexedrine is prescribed in higher doses to treat people with narcolepsy, the medication can have a stimulating effect and help people stay awake. As with any medication, it is possible to overdose on Dexedrine. Seek immediate medical attention if you believe you are experiencing symptoms of a Dexedrine overdose, such as hallucinations, shakiness, or fast breathing.