information on smoking using a series of questions. Participants who responded positively to the questions “having ever smoked” and “having smoked in the past 30 days” were asked to indicate whether they smoked weekly. Response to this item was used as a binary indicator of regular smoking. We classified participants as having used illicit drugs other than cannabis if they indicated they had used any of the following substances over the past 12 months: cocaine, amphetamines, inhalants, sedatives, hallucinogens, or opioids.
