MA use triggers the activation of the sympathetic nervous system which controls many functions of the brain and other organs including blood pressure, heart rate, mood and appetite. In addition, the sympathetic nervous system controls the “fight or flight” response. By triggering the sympathetic nervous system, MA use may cause :
Initially at least, MA can produce effects that many users find desirable; for example, an increase in energy, wakefulness, attention, self-confidence, and sexuality; a decrease in appetite; and a sense of euphoria. Although MA may increase energy and attention, there is little evidence to suggest that it is a “smart drug.” Studies have found no evidence showing positive effects of methamphetamine on various cognitive tests or measures of intelligence.
MA use can also produce insomnia, nausea, dizziness, anorexia, irritability, impulsivity, impaired judgment, irrational thoughts, suspiciousness/paranoia, and possibly a propensity towards violence. Use of MA can also lead to stereotyped behavior called "punding," which is defined as ‘an organized goal-directed but nevertheless meaningless activity’ and as ‘an autonomic behavior with something of the compulsive factor.’ MA users, especially those who use the drug frequently and in high doses, may participate in various repetitive behaviors such as car washing, home cleaning, and dismantling and reassembling objects.