Methamphetamine is a strong physical and mental stimulant available in both prescription and street forms. It is relatively easy to synthesize which has contributed to its widespread use.
Negative effects of methamphetamine use are: disturbed sleep patterns, tightening of jaw muscles, grinding of teeth, reduced enjoyment of eating, loss of interest in sex, excessive itching of skin, nausea, vomiting, diarrhea, blood found in bowl movements, hyperactivity, shortness of breath, moodiness and irritability, anxiousness and nervousness, agressiveness and violent behavior, abnormal panicking, suspiciousness and paranoia, involuntary bodily movements (twitching), severe depression, suicidal tendancies.
Long-term use is known to lead to fatal kidney and lung disorders, brain damage (some is irreversible), permanent psychological problems, lowered resistance to illnesses, liver damage, stroke.
Users of large amount of amphetamines over a long period of time can develop an amphetamine psychosis, which is a mental disorder similar to paranoid schizophrenia. The psychosis is manifested by hallucinations, delusions, and paranoia. Bizarre, sometime violent, behavior is exhibited by those with amphetamine psychosis. Symptoms usually disappear within a few weeks after drug use stops.
Dude--"Nah, man. That shit's dangerous."