A teenager who smokes and drinks is more likely to abuse prescription painkillers as a young adult, according to a new Yale study.

Researchers at the Yale School of Medicine analyzed nationally-representative survey data to explore a possible link between alcohol, cigarette, and marijuana use as an adolescent and subsequent abuse of prescription pain medication as a young adult. Their paper, published in the Journal of Adolescent Health, was the first to find that a link between these “gateway drugs” and prescription painkillers. They found that all three drugs are associated with higher levels of prescription drug abuse in men, but only marijuana use is associated with higher levels of prescription drug abuse in in women.

The number of Americans abusing prescription opioids — drugs like Vicodin and Percocet — has exploded over the past decade, said Lynn Fiellin MED ’96, an associate professor of medicine at the School of Medicine and lead author of the study. According to the Centers for Disease Control and Prevention, in 2010 more than 12 million Americans reported using prescription painkillers that their doctors had not prescribed for them.

“Part of our aim was to demonstrate how the emerging epidemic of prescription opioids is a major issue that the general population doesn’t recognize,” Fiellin said. “They don’t recognize that that abuse does fall into the same category as hard, illicit drugs.”

According to Steve Bernstein, an associate professor of emergency medicine at the Medical School who was not affiliated with the study, prescription painkillers have presented a particularly difficult problem for doctors to negotiate. Over the past 20 years, he said, there has been an increasing focus on the adequate treatment of pain. In an effort to aid patients, doctors have been prescribing more painkillers, which has had the unintended effect of feeding the growing black market for the drugs.

Fiellin said that in order to understand why the number of young adults abusing prescription drugs has increased, it is important to examine their drug habits as adolescents.

The researchers used data from 2006 to 2008 from the National Survey on Drug Use and Health, an annual study representative of the U.S. population, to study 18- to 25-year-olds’ drug use behavior. They found that 12 percent of the survey population reported misusing prescription opioids around the time the survey was conducted.

They also found that both men and women who had smoked marijuana between the ages of 12 and 17 were more than two times more likely to later abuse prescription drugs than those who had not. Young men who drank or smoked cigarettes as teens were 25 percent more likely to abuse prescription drugs — though this link was not found in women surveyed. Fiellin said there was no clear-cut reason why the results differed for men and women.

Keith Humphreys, professor of psychiatry at the Stanford Medical Center, said that this association between “gateway drugs” and prescription pain medication was significant regardless of the exact mechanism behind the link.

“Some people believe the ‘gateway effect’ exists because early drug use primes the human brain for more drug-seeking, others argue that the friends you make using drugs as a youth are a ready source for other drugs later, and still others argue that there are factors, like impulsivity, that causes both early and later drug use,” Humphreys said. “Which camp is correct? Probably, all of them.”

This argument would point to the fact that more interventions are needed earlier on in adolescents’ lives, Bernstein said. He said that it may be valuable to conduct a longitudinal study that would track children from a young age to see whether drinking or smoking actually caused later prescription drug abuse.

But, he said, it would be a mistake to wait for more concrete research before creating programs and policies aimed at prevention.

“You’d never intervene otherwise because you’ll never have perfect data,” Bernstein said. “The only way to really know would be to do a randomized trial — to have some people smoke and drink, and the others to stay abstinent — but of course that’s unethical.”

But Fiellin cautioned that though a significant link was found in the data, it’s harder to know whether the findings will be meaningful in practice.

The study was funded with grants from the National Institute on Drug Abuse and the Department of Veteran’s Affairs in West Haven.