['Marijuana and tobacco are the substances used most commonly by adolescents and co-occurring use is common. Use of one substance may potentiate the addictive properties of the other. The current study examined the severity of nicotine addiction among teen smokers as a function of co-occurring marijuana use.', 'Participants were 165 adolescents (13-17 years old) who reported smoking at least 1 cigarette per day (CPD) in the past 30 days. General linear models examined the association of marijuana use with multiple measures of nicotine addiction including the Modified Fagerström Tolerance Questionnaire (mFTQ), Hooked on Nicotine Checklist (HONC), ICD-10, and the Nicotine Dependence Syndrome Scale (NDSS).', 'The adolescent sample (mean age=16.1 years, SD=0.95) averaged 3.0 CPD (SD=3.0) for 1.98 years (SD=1.5). Most (79.5%) also smoked marijuana in the past 30 days. In models controlling for age, daily smoking status, and years of tobacco smoking, frequency of marijuana use accounted for 25-44% of the variance for all four measures of adolescent nicotine dependence.'] Is frequent marijuana use associated with greater nicotine addiction in adolescent smokers?