Methamphetamine is a stimulant which is generally produced in large laboratories in Mexico , the United States and Asia, or in small "toxic labs" in the United States . It can be injected or smoked. "Ice" is the crystallized form of methamphetamine and it is generally smoked. In all its forms, methamphetamine is highly addictive and toxic.

The onset of meth effects is about the same as cocaine, but they last longer. Meth remains in the central nervous system longer than cocaine, and chronic abuse produces a psychosis that resembles schizophrenia, and is characterized by paranoia, picking at the skin, preoccupation with one's thoughts and auditory and visual hallucinations. These effects can last for months and even years after using methamphetamine and violent and erratic behavior is often seen among chronic users.

Effects 

Increased alertness, excitation, euphoria, increased pulse rate and blood pressure, insomnia and loss of appetite.

Agitation, increased body temperature, hallucinations, convulsions, possible death.

Crank, Ice, Crystal, Krystal Meth, Speed

(Excerpts from justthinktwice.com)