Amphetamines

Amphetamines, according to recent research, act on the neurotransmitters of the brain to produce their mood-altering effects. The two main neurotransmitters affected are dopamine and norepinephrine, produced by cells in the brain. Amphetamines appear to stimulate the production of these two neurotransmitters and then prevent their uptake by other cells. They further increase the amount of surplus neurotransmitters by inhibiting the action of enzymes that help to absorb them into the nervous system. It is believed that the excess amount of neurotransmitters caused by the amphetamines are also responsible for the behavioral changes that follow a high.

Drugs that pose a high risk of addiction like amphetamines, opiates, and cocaine all seem to arouse the centers of the brain that control the urge to seek out pleasurable sensations. Addictive drugs overcome those centers and displace the urge to find pleasure in food, sex, or sleep, or other types of activity that motivate people not addicted to drugs. The drug addict's primary concern is to relive the pleasure of the drug high, even at the risk of "crashing" (coming down from the high in a painful way) and in the face of the social disapproval the habit inevitably entails. Laboratory experiments have shown that animals self-administering amphetamines will reject food and water in favor of the drug. They eventually perish in order to keep up their supply of the drug.

Withdrawal symptoms for chronic users include depression, anxiety, and the need for prolonged periods of sleep.