Methamphetamine increases wakefulness and has a generally invigorating effect on the body and the mind, including euphoria. The most important effects are:
- A feeling of alertness and sharpened senses;
- Reduced need for sleep, insomnia;
- Increase physical activity;
- Reduced appetite;
- Increased self-confidence;
- Exhilaration, talkativeness, restlessness, irritability;
- Increased metabolism;
- Impairment of judgment and reduced inhibitions in some cases leading to outright recklessness; and
- Initially, heightened sense of sexuality. After a long time of abuse, however, the sexual drive decreases.
Respiratory effects include increased respirations, damage to small blood vessels in the lungs, and decreased lung capacity. Cardiovascular effects include increased heart rate and blood pressure, abnormally rapid heart beat and heart palpitations, and possibly irreversible, stroke-producing damage to small blood vessels in the brain.
The dangerous combination of increased heart rate and activity along with constriction of veins and lung capacity can lead to the risk of overdose characterized by dehydration, breakdown of muscle leading to kidney failure, convulsions, stroke and heart attack. Although rare, overdose of can lead to elevation of body temperature to dangerous levels (hyperthermia), which, if not treated immediately, can result in death.
The typical withdrawal symptoms from ATS are the opposite of the effects from acute intoxication, and typically begin several days after abstinence. This is in contrast to withdrawal from opiates which begins within a few hours. The most common withdrawal symptoms with ATS are fluctuating feelings of fatigue and unrest, irritability, long but troubled sleep, intense hunger, and moderate to severe depression, which for some abusers may lead to suicidal behavior. Memories of the euphoric effects contrasting with the unpleasantness of withdrawal often induce a strong craving for ten weeks or longer and may lead to relapse.