Teens who smoke pot but not cigarettes appear to be more likely to get good grades, play sports and live with both parents than those who also use tobacco, finds a surprising new study from Switzerland.

What's more, the study found that teens who smoke pot were more likely to have a good relationship with their friends than teens who smoked neither tobacco nor pot, found the study published in the November issue of Archives of Pediatrics & Adolescent Medicine.

To conduct the study Dr. J. C. Suris and colleagues at the University of Lausanne, Switzerland, analyzed data from a 2002 national survey of almost 5,300 Swiss students aged 16 to 20 years. Of the group, 455 smoked marijuana exclusively, 1,703 smoked marijuana and tobacco, and 3,105 abstained from both substances.

The survey also found that, compared with students who used both substances, students who smoked marijuana only were more likely:

• to be male (71.6 per cent vs. 59.7 per cent),
• to play sports (85.5 per cent vs. 66.7 per cent)
• to live with both parents (78.2 vs. 68.3)
• to have good grades (77.5 vs. 66.6).

As well, the researchers noted that students who smoked marijuana only were less likely:

• to have been drunk in the past 30 days (40.5 per cent vs. 55 per cent)
• to have started using cannabis before the age of 15 years (25.9 per cent vs. 37.5 per cent)
• to have smoked marijuana more than once or twice during the previous 30 days (44 per cent vs. 66 per cent)
• to use other illegal drugs (8.4 per cent vs. 17.9 per cent).

Those who smoked marijuana only used it less often than those who smokes both cigarettes and pot. About half of the tobacco-and-marijuana group had used pot 10 times or more in the previous month, compared to about half in the marijuana-only group who had used the drug only once or twice in the same time period.

Compared to teens who abstain from smoking pot or cigarettes, pot-only smokers are more likely to skip class, but still have the same level of good grades. And although they were more likely to report having a relationship with their parents, they are not more likely to be depressed than abstainers. 

The study did not explain the reasons behind any of its findings.

The authors note that although teens who smoke both marijuana and tobacco seem to have more psychosocial problems, those who smoke marijuana only should be monitored closely too. They note as well that marijuana use has increased in recent years among teens in Switzerland and other European countries.

"The situation of those adolescents who use cannabis but who declare not using tobacco should not be trivialized," the authors conclude.