The scientists surveyed 5,263 Swiss students (2,439 females) aged 16 to 20 years, including 455 who said they smoked weed only; 1,703 who reported being tobacco and marijuana users; and 3,105 who said they did not imbibe at all.
"The gateway theory hypothesizes that the use of legal drugs (tobacco and alcohol) is the previous step to cannabis consumption," the authors wrote. "However, recent research also indicates that cannabis use may precede or be simultaneous to tobacco use and that, in fact, its use may reinforce cigarette smoking or lead to nicotine addiction independently of smoking status."
Among their findings: Compared with students who reported using both drugs, those who smoked pot only were more likely to be male (71.6 percent versus 59.7 percent); get good grades (77.5 to 66.6 percent); play sports (85.5 to 66.7 percent); and live with both parents (78.2 to 68.3 percent).
Cannabis-only smokers were also less likely than their cigarette-and-joint smoking brethren to have used other illegal drugs or to have been soused or have used pot more than twice in the previous 30 days, according to the study.
In contrast to those who shunned both substances, the pot-only crowd was more likely to be male (71.6 to 47.7 percent); have a good relationship with friends (87 versus 83.2 percent); and play sports (85.5 versus 76.6 percent). They were less likely than the abstainers, however, to get along well with their parents (74.1 percent compared with 82.4).
The researchers stressed that whereas students who smoked and toked seemed more prone to psychosocial problems, the marijuana-only users should not be dismissed.
"Even though they do not seem to have great personal, family or academic problems," they wrote, "the situation of those adolescents who use cannabis but who declare not using tobacco should not be trivialized."
Groups working toward the decriminalization of marijuana especially for medical purposes praised the findings.
"Studies like this show associations, not cause and effect," says Bruce Mirken of the Washington, D.C.–based Marijuana Policy Project, a lobby that believes marijuana should be legalized but also regulated and taxed much like cigarettes and alcohol. "But the drug czar's office regularly uses associations between marijuana use and problems like poor grades to frighten parents into thinking that cause and effect is proven. So will [it] now say that smoking marijuana makes teens have better peer relationships and be more likely to participate in sports?"
"No one wants to encourage teens to smoke marijuana," he adds, "but this study strongly suggests that the most serious problems for teens and parents isn't occasional marijuana use, but heavy use of multiple substances, which is likely a sign of kids who are seriously troubled and need help."