Psychostimulants

Psychostimulants, including cocaine and amphetamines, have become increasingly popular in the United States.

Crack cocaine enters the bloodstream through the lungs. Within seconds, it is carried by the blood to the brain. The basis for increased pleasure occurs at the synapse. Dopamine-containing neurons normally relay their signals by releasing dopamine into many synapses. Dopamine crosses the synapse and fits into receptors on the surface of the receiving cell. This triggers an electrical signal that is relayed through the receiver. Then, to end the signal, dopamine molecules break away from the receptors and are pumped back into the nerve terminals that released them. Cocaine molecules block the pump, or transporter, causing more dopamine to accumulate in the synapse. Pleasure circuits are stimulated again and again, producing a sense of euphoria.

In 2009, in the United States, an estimated 4.8 million people age 12 and older had abused cocaine. A popular, chemically altered form of cocaine, crack, is smoked. It enters the brain in seconds, producing a rush of euphoria and feelings of power and self-confidence. A form of methamphetamine that can be smoked, “crystal meth,” also has become popular.

The key biochemical factor underlying the reinforcing effects of psychostimulant drugs is their ability to greatly elevate the brain chemical dopamine in specific brain regions, such as the nucleus accumbens. Alterations in dopamine activity in the accumbens, induced by chronic cocaine intake, are thought to result in a progressively increasing motivation to take the drugs, eventually leading to addiction.

Cocaine users often go on binges, consuming a large amount of the drug in just a few days. A crash occurs after this period of intense drug-taking, resulting in such symptoms as emotional and physical exhaustion and depression. These symptoms may come from an actual shutdown, or crash, in dopamine and serotonin function, as well as an increased response of the brain systems that react to stress. Vaccines to produce antibodies to cocaine in the bloodstream are in clinical trials.