Methamphetamine (meth for short) is a psychostimulant that can be found occurring naturally in some variations of the acacia tree. It is, however, most commonly produced by synthesizing certain caustic chemicals and OTC stimulants. The resulting product of this synthesizing process is a poisonous substance that includes not only the methamphetamine compound, but many additional toxins as well. In this form, it is commonly known as crystal, crystal meth, crank, etc.
Meth is very addictive as well as destructive. Withdrawal effects are similar to those of cocaine, amphetamines, and nicotine (to a much greater degree).
Serial killer Eddie Mays (Blood Hungry) and bank robber Caleb Dale Sheppard (Psychodrama) were known meth addicts. Billy Flynn (Our Darkest Hour and The Longest Night) regularly smoked crystal meth in order to stay awake at night.