Substance Abuse Research

Youths' Opportunities To Experiment Influence Later Use of Illegal Substances
NIDA-supported researchers have reported new epidemiological evidence about the associations linking earlier alcohol or tobacco use with later use of marijuana, and the link from earlier marijuana use to later use of other illegal drugs such as cocaine and hallucinogens. This study builds on the many prior NIDA-supported studies of the "gateway" theory of youthful substance involvement: Once use of tobacco or alcohol begins, there is greater likelihood of marijuana use, and once marijuana use begins, there is greater likelihood of other illegal substance use.

"This research increases our understanding of the complex relationship between the different stages of substance use and raises concerns about factors that promote the transition from opportunities to initiate substance use to patterned use," says Dr. Kathleen Etz of NIDA's Division of Epidemiology, Services and Prevention Research. "We know that earlier substance use is associated with later, more advanced use. However, this research identifies a previously overlooked aspect of this transition, opportunities to use."

Using annual data from the 1991 through 1994 National Household Survey on Drug Abuse (NHSDA), the research team led by Dr. James C. Anthony from Johns Hopkins University Bloomberg School of Public Health in Baltimore, analyzed the responses of 26,015 individuals aged 12 to 18 who answered questions regarding marijuana use and the responses of 44,624 individuals aged 12 to 25 who answered questions regarding cocaine use. The research focused on a concept called "substance exposure opportunities." This concept takes into account that some young people actively seek out opportunities to try marijuana or cocaine, whereas others are more passive recipients of substance exposure opportunities.

The researchers found that alcohol and tobacco users were more likely than nonusers to have an opportunity to try marijuana and were also more likely to try the substance when the opportunity arose. About 75 percent of alcohol or tobacco users reported an opportunity to try marijuana by age 18, and more than 85 percent of them made the transition to marijuana use. Only about 25 percent of nonsmokers and nondrinkers were given an opportunity to try marijuana by the same age. Of these, fewer than 25 percent began smoking marijuana within 6 years after they were first given the opportunity. Overall, alcohol or tobacco users were seven times more likely to start using marijuana than individuals who had used neither alcohol nor tobacco.

Prior marijuana use was closely associated with the opportunity to try cocaine and the likelihood of young people's starting to use cocaine once given the opportunity. Among the young people who were given the chance to try cocaine, those who were already using marijuana were 15 times more likely to use cocaine than those who did not use marijuana. About 50 percent of marijuana users used cocaine within 2 years of their first opportunity to do so. However, among young people who never used marijuana, fewer than 10 percent initiated cocaine use.

In a separate but related study, the researchers analyzed data from 41,271 young people who participated in the 1991 through 1994 NHSDA. They investigated the relationship between the use of marijuana and use of hallucinogens. The results showed that marijuana users are more likely than nonusers to be offered an opportunity to use LSD, mescaline, mixed stimulant-hallucinogens, and PCP and more likely than nonusers to try these hallucinogenic drugs when they're offered. By age 21, nearly one-half of the teenagers who had smoked marijuana were presented with the opportunity to try hallucinogens, compared to only one-sixteenth of those who had not used marijuana. Once given the opportunity to use hallucinogens, marijuana smokers were about 12 times more likely to use hallucinogens than those who did not use marijuana.

"These studies are the first to support the idea of two separate mechanisms linking the use of alcohol, tobacco, marijuana, cocaine, and hallucinogens. One mechanism involves increased drug exposure opportunity, and a separate mechanism involves increased likelihood to use once the opportunity occurs," says Dr. Anthony. "Even if there is an underlying common vulnerability or predisposition that accounts for the observed sequencing of substance exposure opportunities and actual substance use, these observations may have implications for the design and evaluation of drug prevention activities. Drug users often are members of social circles where drug use and experimentation are more common and friends are likely to share drugs. In addition to trying to persuade young people not to use drugs, it may be worthwhile for us to persuade users not to share their drugs with friends." Previous research has also shown that although males are more likely than females to have opportunities to use drugs, both are equally likely to make a transition into substance use once an opportunity to try a substance has occurred. Dr. Anthony and his colleague, Dr. Fernando Wagner, also from Johns Hopkins University Bloomberg School of Public Health, have made similar observations in ongoing research studies.

Dr. Anthony believes that his research carries a strong message for parents and pediatricians, who often neglect the opportunity to ask children and adolescents about whether they have had chances to try illegal drugs. As Dr. Anthony notes, "Kids will talk to us about their chances to try illegal drugs even when they are unwilling to talk about actual drug use. Once the chance to try marijuana or cocaine occurs, it is a red flag, and we need to be paying close attention to what happens next."

"Future research in this area will be a great asset to the development of effective substance prevention programs," says Dr. Etz. "It will assist us in understanding the process through which the use of one substance is related to use of another and help us to target prevention programs to individuals more likely to progress to advanced substance use."

Research Study Sheds Light on Progression to Substance Abuse
An understanding of the circumstances that lead from first use of a substance to substance abuse can lead to the development of more effective prevention programs. NIDA-supported researcher Dr. James Anthony and colleagues at the Johns Hopkins University examined research data from the National Comorbidity Survey (NCS) to determine the ages at which individuals are at greatest risk of starting to use marijuana or cocaine and to map their patterns of progression to dependence on the drugs. The NCS, conducted between 1990 and 1992, was designed to gather comprehensive mental health information about the U.S. population and involved detailed interviews with more than 8,000 women and men aged 15 to 54.

The research data compiled found that first use of marijuana occurs on average at age 18 and roughly 9 percent of users will become dependent on the substance, most likely before age 25. For cocaine, first use is most likely at age 20 and progression to dependence is more rapid. The peak incidence of transition to dependence occurs between ages 23 and 25. Roughly 21 percent of persons who use cocaine at least once will become dependent, most likely by age 45.

"These patterns illustrate the cumulative risk of continued substance use," says Dr. Coryl Jones, formerly of NIDA's Epidemiology Research Branch. "For some, using marijuana or cocaine once or twice may not lead to dependence, but the risk is always there. Factors such as health, personal problems, or stress may slowly or suddenly combine to tip the balance from substance use to substance abuse."