"Knowing that ADHD increases the risk of more serious nicotine addiction stresses the importance of prevention efforts aimed at adolescents and their families," says Timothy Wilens, MD, director of the Substance Abuse Program in the MGH Pediatric Psychopharmacology Department, who led the study. "It also gives us clues about how the neurotransmitter systems involved in ADHD and tobacco use may be interacting."
Several studies have shown young people with ADHD are more like to smoke and to start smoking at an earlier age. The current investigation was designed to examine whether ADHD also increases the severity of nicotine dependence. Participants were taken from two long-term studies – one in boys and the other in girls – that analyzed a variety of factors in children and adolescents with ADHD compared with a matched control group. Participants completed a standardized questionnaire evaluating smoking history and levels of tobacco dependence in current smokers. Responses from 80 participants with ADHD and 86 controls, all ranging from age 15 to 25, were available for analysis.
While 69 percent of participants with ADHD had ever smoked and 41 percent were current smokers, only 44 percent of controls had ever smoked, with 17 currently smoking. Smokers with ADHD began using tobacco about a year and a half sooner than did control group members, and moderate or higher levels of nicotine dependence were reported by 21 percent of AHDH participants but less than 1 percent of controls.
The two larger studies in which participants enrolled had included assessments of psychiatric symptoms, including those associated with ADHD. For both participants with ADHD and the controls, the more ADHD-related symptoms such as prominent inattention, distraction, overactivity or impulsivity the smokers had, the more serious their dependence on nicotine. A similar increase in tobacco dependence was associated with living with a smoker or having a parent or friend who smoked in ADHD participants but not in controls, implying that the vulnerability to smoking bestowed by ADHD was amplified by environmental factors, Wilens explains.
The study's findings also suggests biological mechanisms that may underlie both ADHD and nicotine dependence. "We've already shown that nicotine-based medications can treat ADHD symptoms, and it's known that the children of mothers who smoked during pregnancy are at greater risk of ADHD," Wilens says. "It looks like interplay between the dopamine system, more substantially related to ADHD and addiction, and the cholinergic system related to smoking is probably important. Further investigations of the neurobiological aspects and potential issues of self-medication should help us better understand what is going on." Wilens is an associate professor of Psychiatry at Harvard Medical School.
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