A study from the Johns Hopkins Bloomberg School of Public Health provides the first epidemiological evidence that young marijuana smokers are substantially more likely than nonsmokers to be presented with the opportunity to try hallucinogens. Once that opportunity occurs, marijuana smokers are more likely than nonsmokers to actually try hallucinogens. The study appears in the April issue of Drug and Alcohol Dependence.

"Research in the past has focused on the causal relationships of drugs, but our study is the first to support the idea of two separate mechanisms linking marijuana and hallucinogen use--that of increased opportunity and increased use once given the opportunity," says lead author Holly Wilcox, a doctoral candidate in the Department of Mental Hygiene. "Insight into this area teaches us about mechanisms that might help guide new progress for prevention of drug problems."

For the investigation, the researchers used self-report data from more than 40,000 young participants in the 1991 to 1994 National Household Surveys on Drug Abuse. From the NHSDA data, they were able to extract information about the age at which young people first had the opportunity to use different drugs and the age at which they first tried them. They focused on the availability and use of two drugs: marijuana (cannabis, reefer, blunts, hash oil or any other form of marijuana use) and hallucinogens (LSD, mescaline, mixed stimulant-hallucinogens and PCP).

The results showed that by age 21, almost one-half the teenagers who had smoked marijuana had had a chance to try a hallucinogen, compared to only one in 16 of the teenagers who had never smoked marijuana. Within a time period of one year after the first chance to use a hallucinogen, two-thirds of marijuana smokers had actually tried it, compared to only one in six of the teenagers who had never smoked marijuana.

According to James C. Anthony, a professor of mental hygiene, psychiatry and epidemiology, "This large difference between marijuana smokers and nonsmokers may be attributed to the social influences in a marijuana smoker's life. Young people who are using marijuana sometimes develop contacts with illegal drug dealers who may try to push other drugs like Ecstasy or LSD," he says. "Also, marijuana smokers often are members of social circles where drug use and experimentation is more common, and friends are likely to share drugs. In addition to trying to persuade young people to not use drugs, it may be worthwhile for us to persuade users to not share their drugs with friends."

The authors say further research is needed to account for variations in exposure opportunities experienced by marijuana smokers and to understand why some marijuana smokers choose not to use hallucinogens once given the opportunity. "Such research should lead toward new ideas for prevention of hallucinogen use," Wilcox says.

The study was supported by grants from the National Institute on Drug Abuse and support from the National Council on Science and Technology, Mexico.