- The Washington Times - Wednesday, January 22, 2003

Young teens who smoke marijuana are two to five times more likely to use other illicit drugs than their nonsmoking peers, says a study released today in a leading medical journal.
The findings support the "gateway hypothesis," which says marijuana use opens the door to "harder" drugs, such as cocaine and heroin.
"It is apparent that young people who initiate cannabis use at any early age are at heightened risk for progressing to other drug use and drug abuse/dependence," wrote Michael T. Lynskey, lead author of the study in today's Journal of the American Medical Association (JAMA).
Doctors and drug-treatment leaders are well advised to take teen marijuana use seriously, both because it can cause lung damage and because it poses a real risk that the user will progress to other drugs, said Mr. Lynskey, who studies cannabis issues at the Washington University School of Medicine in St. Louis.
The Lynskey study, involving 311 sets of same-sex adult twins from Australia, makes a "unique contribution" to the debate about whether genetics, family environment or marijuana itself causes some users to move on to more serious illegal drugs, Denise B. Kandel, a professor of psychiatry at Columbia University, wrote in a JAMA editorial.
The Australian twins were chosen because they shared genetic characteristics, were raised in the same environment and, in each case, one twin used marijuana before age 17 while his or her sibling did not.
Researchers theorized that if genetics or environment were the most important factors, each set of twins' drug use would be about the same; if one twin became dependent on drugs or alcohol, so would the other.
Instead, they found that, controlling for many factors, the twins who used marijuana before age 17 were 2.1 to 5.2 times more likely to use illegal drugs and/or become dependent on drugs or alcohol than their siblings who didn't use marijuana before age 17.
For instance, 47.9 percent of the young marijuana smokers went on to use cocaine or other stimulant drugs, while 26.4 percent of their siblings did.
The results held true even if the other sibling started using marijuana after age 17.
The study speculates that early marijuana use may lead to later drug abuse because initial experiences with marijuana are pleasurable and "seemingly safe." Most young people aren't arrested even though cannabis is illegal, Mr. Lynskey said, and using marijuana also connects a young person to people who traffic in all kinds of illicit drugs.
Moreover, he said, smoking marijuana may cause biochemical changes that encourage drug-taking behavior, though more research is needed on these issues.

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