Methamphetamine (meth) is a powerfully addictive stimulant, can be easily produced in illicit, makeshift laboratories and generally is considered the fastest-growing illicit drug in the United States. Meth is available as a crystalline powder or in rock-like chunks. Meth varies in color, and may be white, yellow, brown or pink. Meth can be smoked, injected or snorted. Immediately after smoking or injection, the user experiences an intense sensation, called a "rush" or "flash," that lasts only a few minutes and is described as extremely pleasurable. Following the "rush," users will experience a state of high agitation that can lead to aggressive or violent behavior. Other short-term symptoms include increased wakefulness and physical activity and decreased appetite. It can also cause heart problems, including rapid heart rate, irregular heartbeat, and increased blood pressure. Hyperthermia (elevated body temperature) and seizures may occur with methamphetamine overdose, and if not treated immediately, can result in death.

Long-term effects include tolerance - very quickly users will need larger amounts to get high. In some cases, users will take more meth every few hours for days, until they either run out of the drug or become too dysfunctional to continue using. Other long-term effects include paranoia, hallucinations, repetitive behavior (such as compulsively cleaning and grooming or disassembling and assembling objects), and delusions of parasites or insects crawling under the skin. Users can obsessively scratch their skin to get rid of these imagined insects. Long-term use, high dosages, or both can induce full-blown toxic psychosis. This behavior is usually coupled with extreme paranoia. Unfortunately, the psychotic symptoms can sometimes last for months or years after a person has quit abusing methamphetamine, and stress has been shown to precipitate spontaneous recurrence of methamphetamine psychosis in formerly psychotic methamphetamine abusers.[i]

From a neurological standpoint, meth actually changes brain chemistry, and after extended use, the brain can no longer respond to normal brain transmitters. The result is that users can no longer feel good, and they resort to increase consumption of the drug in an attempt to recapture the first high. At this point, the user often becomes addicted.

Finally, long-term users also suffer physical effects, including weight loss, severe tooth decay and tooth loss ("meth mouth"), and skin sores. The dental problems may be caused by a combination of poor nutrition and dental hygiene, as well as dry mouth and teeth grinding caused by the drug. Skin sores are the result of picking and scratching the skin to get rid of insects imagined to be crawling under it.