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Why Do People Take Drugs in the First Place?

People who use drugs, including alcohol, do so because they like what the drugs do to their brains. All drugs of abuse, from alcohol to nicotine to heroin, cause a series of temporary changes in the brain that produce the "high."

One of these changes is the rise in available levels of certain neurotransmitters associated with feelings of pleasure. Key among these is dopamine, a naturally occurring neurotransmitter that some scientists now think is implicated in most of the basic human experiences of pleasure.

The pleasure of a kiss, a bowl of favorite ice cream, and a compliment may all be related to a rise in dopamine levels in the normal person's brain. Drugs of abuse also boost dopamine levels. When a person takes a hit of crack cocaine -- or a drag on a cigarette -- the drugs cause a spike in dopamine levels in the brain, and a rush of euphoria, or pleasure. While it's not the only chemical involved in drug abuse, experts have come to believe that dopamine is the crucial one.

A 1997 study led by researcher Dr. Nora Volkow of the Brookhaven National Laboratory in Upton, NY, found a significant relationship between the intensity and duration of the rush associated with cocaine and the degree to which the drug blocks one of the key mechanisms that control the amount of dopamine in the brain. Previous animal studies have shown that cocaine occupies or blocks dopamine transporter sites and prevents dopamine from returning, as it normally would, to the brain cells that release it. This allows high concentrations of dopamine to remain available in the brain longer than normal, which is believed to cause the high associated with cocaine use. (See animation.) Elevated dopamine levels make a person feel omnipotent. "You get a sense of power, a sense of being able to do things, an immediate feeling of pleasure associated with moving and getting going and being unusually capable," says George Koob, M.D., a professor in the neuropharmacology department at the Scripps Research Institute.
 

Brain MAO B and smoking status

PET scans showing that the brain of a smoker has less of the enzyme MAO B than that of a non-smoker. MAO B breaks down the "pleasure chemical" dopamine in the brain.

Close to Home Animations

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Animations: How Drugs Work

IN THE BODY

Alcohol, Cocaine, Stimulants, Opiates, Nicotine, Marijuana (22K)

IN THE BRAIN

How Brain Cells Communicate

How COCAINE Works in the Brain:

How ALCOHOL Works in the Brain:

How OPIATES Work in the Brain:

Scientists are now able to actually see this happening. The Brookhaven study, which included researchers from State University of New York at Stony Brook and Columbia University, examined PET scans of 17 current cocaine users. Researchers found that high doses of cocaine blocked from 60 to 77 percent of the users' dopamine transporter sites. (For the user to perceive cocaine's effects, about half of the sites had to be blocked, the study found.) Methamphetamine, or speed, produces a similar effect, dramatically boosting the supply of dopamine at brain synapses, which results in increased stimulation and feelings of euphoria.

New research has also revealed that a chemical in cigarette smoke may keep dopamine in synapses by blocking an enzyme (called monoamine oxidase or MAO) designed to break it down. A study by the Department of Energy's Brookhaven Laboratory found that smokers had an average of 40 percent less of the enzyme MAO B (a subtype of MAO) than non-smokers and former smokers. Less MAO B could result in enhanced dopamine activity, rewarding and reinforcing the behavior that caused the increase in dopamine behavior such as smoking.

-- Janet Firshein

Normal/Cocaine Activity: Courtesy of NIDA
Scans: Courtesy of Brookhaven National Laboratory Center for Imaging and Neurosciences

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ANIMATIONS | Differences | Crossing the Line | Relapse | Why Drugs? | Similar Effects | Dependence | Vulnerability | Changing Back | Interviews

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