There has been much debate in recent years as to whether or not marijuana is a “gateway” drug – a drug that paves the way to the use of alcohol and other addictive substances. As marijuana continues to be legalized in many states across the U.S., a new vigor has become apparent in discussions of the safety or usefulness of cannabis. Many now seem to have a vested interest – with no small measure of that interest being financial – in showing that marijuana is a “good” thing.
A new longitudinal study by British scientists is calling that reasoning into question, providing evidence that marijuana use among young people increases the likelihood that they will use other illegal substances as young adults.
The study, published this week in the Journal of Epidemiology and Community Health, revealed that teens who regularly or occasionally use pot are more likely to take other illegal drugs or use other harmful substances by age 21, adding weight to the idea that marijuana does indeed act as a “gateway” to the use of other drugs.
In the study, researchers found that teenagers who regularly used marijuana were 26 times more likely to have used other illegal drugs, such as cocaine, amphetamines, or hallucinogens by the time they reached early adulthood, compared with teens who hadn’t smoked pot.
It also revealed that the teens who used marijuana once a week or more were 37 times more likely to be hooked on nicotine, and three times more likely to have harmful drinking habits by age 21 than their peers who did not use marijuana.
“The findings show that the more an individual uses marijuana during adolescence, the more likely he or she will develop problematic substance use behaviors in early adulthood,” said lead study author Michelle Taylor, a senior research associate in epidemiology at the University of Bristol in England.
Previous studies have yielded only mixed results when they looked at whether using marijuana during adolescence increases the likelihood of use of other illegal drugs in early adulthood. The evidence of a link between teen marijuana use and later tobacco use or alcohol problems has also been inconsistent.
In the new study, researchers analyzed data from the Avon Longitudinal Study of Parents and Children, a long-running study in the U.K. that has followed women and their children for twenty-some years. The study began when the women were first pregnant, all in 1991 or 1992.
For the new report, the researchers looked at questionnaires that more than 5,300 of the children completed. The kids were surveyed at least three times between ages 13 and 18, and asked about the frequency of their use of drugs, alcohol, and tobacco in the previous three months. They were also sent a follow-up survey by mail to measure these behaviors at age 21.
The researchers took into consideration the smoking, drug, and alcohol habits of the teens’ mothers, both when they were pregnant and when the child was growing up, because a mother’s habits can influence her child’s chances of developing similar behaviors as a teen or young adult, the researchers said.
Surveys from the teen years indicated that about 80 percent of the participants had not used marijuana. But 14 percent of the teens started using marijuana by age 15, using it occasionally, or less than once a week. And 2 percent of them started using marijuana by age 13, also using it occasionally. Slightly more than 3 percent of the teens said they were regular marijuana users, meaning they used it one or more times a week.
Researchers found that the teens who had said they either occasionally or regularly used marijuana were more likely to become tobacco-dependent, have harmful levels of alcohol consumption, and use other illicit drugs in early adulthood.
Study authors noted that although the findings establish a correlation between teen pot use and the use of other illegal drugs by age 21, the study does not show a cause-and-effect relationship between the two. The study was also unable to identify the reasons why teens’ early use of marijuana was linked to a greater likelihood of using other illegal drugs by age 21, but authors speculate that genetic vulnerabilities as well as biological, behavioral, and environmental factors all likely play a role.
Future research will likely focus on teasing out some of the specific reasons behind young peoples marijuana use and progression to other drugs, but this study does represent an important research link between marijuana use and other drug problems in young people which should make intervention and prevention strategies much more successful.