or more were considered to be nicotine users, which was the base measure of nicotine exposure in our analyses. Both cannabis use (defined as having ever tried cannabis) and early cannabis use (initiation before age 18) were examined. The early substance use cutoff of age 18 was selected because it was generally prior to entry into the military and was stringent enough to apply to only a minority of participants. All substance use measures were based on the 1992 telephone diagnostic interview.
