The crystalline, manufactured form of methamphetamine is not only highly toxic and tremendously addictive, but its use can also cause a remarkable amount of brain damage. According to the U.S. Drug Enforcement Agency and the National Institute on Drug Abuse, long-term abuse of the drug creates damage to the user's brain that resembles the damage done by strokes, epilepsy, and Alzheimer's disease.

From : AskMen.com