Many U.S. teen smokers -- even those who only light up occasionally -- also use other drugs, a new study suggests.
Of the 176 teen smokers in San Francisco who took part in the study, 96 percent said they'd used at least two other substances besides cigarettes.
In most cases, those other substances were alcohol, marijuana and other tobacco products. However, 16 percent reported the use of harder drugs, such as cocaine, hallucinogens and Ecstasy, or the misuse of prescription medications.
"Most of these adolescents smoked five or fewer cigarettes a day," said study author Karma McKelvey. She's a postdoctoral fellow at the Center for Tobacco Control Research and Education at the University of California, San Francisco.
"This tells us that multidrug use among adolescents may be more prevalent than we think, and that even kids who smoke only occasionally are likely to be doing other drugs," she said in a university news release.
The researchers also found that teens who used harder drugs at the start of the study were more likely than other teens to have depressive symptoms one, two and three years later.
And the percentage of teens who used harder drugs remained consistent over the study period. This "implies that patterns of smoking and drug use established in adolescence can be chronic and persist over time," McKelvey said.
Depression scores might be used to better identify teens who would benefit from drug prevention and treatment programs, according to McKelvey.
"When you ask a teenager if he or she is a smoker, the most likely answer will be no," she said.
"Adolescents do not necessarily identify as smokers, even if they do occasionally smoke cigarettes. However, kids who do not self-identify as smokers are more likely to be overlooked for inclusion in prevention and cessation programs, the idea being that if they don't smoke, they're less likely to drink or do drugs," McKelvey explained.
"Instead, let's perhaps look at their depression scores," she added. "Let's ask adolescents how they're feeling and doing. Go deeper and find out what's really going on with them."
The study was published Dec. 12 in the journal Addictive Behaviors.