Cocaine

Used as a local anesthetic, cocaine constricts the blood vessels, thereby slowing down blood circulation. It also reduces the sensitivity of nerve endings, especially in the skin, eyes, and areas of the mouth. Because cocaine is a stimulant, it increases the heart and pulse rate and raises blood pressure, causing alertness, insomnia, loss of appetite, and dilated pupils.

Several theories have been proposed to explain the addictive effects of cocaine, which differs from other stimulants in its ability to trap the user in a cycle of continued use. Experiments using animals who are able to self-administer cocaine show that, once the need for cocaine is established, an animal will neglect its hunger and sex drives in order to satisfy the craving for the drug. Rats took cocaine until they died, while monkeys indulged until they exhibited such behaviors as paranoia, hyperactivity, convulsions, and heart failure.

Cocaine, like the opioids morphine and heroin, causes addiction by arousing an intense sense of pleasure. Certain parts of the brain induce pleasurable sensations when stimulated. Unlike the opioids, though, cocaine appears to have a greater access to those parts of the brain known as the limbic system, which controls the emotions. Cocaine stimulates the release of the neurotransmitter dopamine, which is responsible for the stimulation of the limbic system. The drug is therefore more potent than other drugs in being more psychologically rewarding. According to a recent theory, most of the mood and behavior changes brought about by cocaine use is due to the release of excess amounts of dopamine in the reward centers of the brain. The ensuing depression and craving for the drug are caused by dopamine depletion after the effects of the drug wear off.