Illicit drug use was defined as lifetime use 11 or more times of marijuana, cocaine, stimulants, sedatives, opiates, PCP, hallucinogens, solvents, or other illicit drugs. Not all wave 1 participants were assessed for nicotine dependence (Bierut et al., 2008), therefore habitual smoking (at least 20 cigarettes daily for at least 6 months) was used as the nicotine use measure at wave 1. At wave 2, all participants were assessed for nicotine dependence. For both drug and nicotine measures, current use was defined as occurring within the last year. Remitted use at follow-up was divided into 2 categories based on most recent use from 1 to 5 years ago or more than 5 years ago.
