Does Marijuana Use at Ages 16-18 Predict Initiation of Daily Cigarette Smoking in Late Adolescence and Early Adulthood? A Propensity Score Analysis of Add Health Data.

Given the declining trend in adolescent cigarette smoking and increase in general access to marijuana, it is important to examine whether marijuana use in adolescence is a risk factor for subsequent cigarette smoking in late adolescence and early adulthood. Preliminary evidence from a very small number of studies suggests that marijuana use during adolescence is associated with later smoking; however, to control confounding, previously published studies used regression adjustment, which is susceptible to extrapolation when the confounder distributions differ between adolescent marijuana users and non-users. The current study uses propensity score weighting, a causal inference method not previously used in this area of research, to weight participants based on their estimated probability of exposure given confounders (the propensity score) to balance observed confounders between marijuana users and non-users. The sample consists of participants of Add Health (a nationally representative dataset of youth followed into adulthood) who were 16-18, with no history of daily cigarette smoking at baseline (n = 2928 for female and 2731 for male sub-samples). We assessed the effect of adolescent marijuana use (exposure, ascertained at wave 1) on any daily cigarette smoking during the subsequent 13 years (outcome, ascertained at wave 4). Analyses suggest that for females (but not males) who used marijuana in adolescence, marijuana use increased the risk for subsequent daily smoking: OR = 1.71, 95% CI = (1.13, 2.59). We recommend that adolescent marijuana use be viewed as a possible risk factor for subsequent initiation of daily cigarette smoking in women.