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"Gateway" Drugs?

"Gateway drugs" is a term for drugs that supposedly lead to abuse of other substances. Marijuana, for instance, is considered by some to be a gateway to harder drugs. George Koob, M.D., of the Scripps Research Institute says that studies of long-term exposure to cannabinoids, the active ingredient in marijuana, suggest that addiction to one drug could make a person vulnerable to abuse and addiction to other drugs. Cannabis abuse, he says, appears to activate corticotropin-releasing factor, a brain chemical that increases during periods of stress. Consequently, Koob says, this could "lead to a subtle disruption of brain processes that are then 'primed' for further and easier disruption by other drugs of abuse."
 

Whether there is such a thing as a gateway drug is still very controversial, however. Critics of the idea note that even if people who use cocaine started with marijuana, it is not clear that the marijuana use caused or encouraged the cocaine use: The person may simply have encountered marijuana first, and/or is the sort of person more inclined than others to experiment with a variety of illegal drugs. Fewer than one percent of marijuana users go on to become cocaine addicts. What is known is that long-term use of marijuana can produce changes in the brain comparable to that seen after long-term use of other major drugs of abuse such as cocaine, heroin, and alcohol.
 

PET scans: Normal vs. Marijuana Abuser

PET scans show long-term changes in glucose metabolism in the brain of a marijuana abuser, compared to that of a normal brain.

However, there does appear to be a link of some kind between nicotine dependence and alcohol dependence. Whether the link is causal or not is still unclear. Some researchers hypothesize that since alcohol can cause depression, alcoholics may be using nicotine as an anti-depressant. "Most alcohol-dependent people are nicotine-dependent. I don't understand why that association is, but there are a bunch of theories being tested," says Marc Schuckit, M.D., a psychiatrist who teaches at the University of California at San Diego Medical School.

-- Janet Firshein
 

Scans: Courtesy of Brookhaven National Laboratory Center for Imaging and Neurosciences
 

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