In early survey rounds, all respondents were surveyed on their experience with marijuana, which is also referred to in the survey as "grass" or "pot." In round 1, respondents were first asked whether they had ever used marijuana. If so, they reported the age at which they first used the drug. Respondents who answered "don't know," or who refused to answer this retrospective question, continued to receive the question in later rounds until a valid answer was given. If a respondent answers affirmatively to having ever used marijuana, but cannot or will not provide the age at which they first used it, they continue to receive the age question in subsequent rounds.

Beginning in round 2, respondents who had previously provided a valid answer to the question about marijuana were asked whether they had used marijuana since the last interview, even if only once. Rounds 2-15 and rounds 17 then collected additional information on the number of days the respondent smoked marijuana in the 30 days prior to the interview. Finally, questions determined the number of times the respondent used marijuana right before or during school or work in those 30 days. Marijuana use questions were not asked in rounds 16 or 18-20.

Regarding drugs other than marijuana, rounds 2-15 and rounds 17 asked about the use of any drugs such as cocaine, crack, heroin, or any other substance used to get high or to achieve an altered state. Details collected include the respondent's age when he or she first used any of these drugs and the number of times since the last interview that the respondent took some drug or other substance. The number of times in the last 30 days that the respondent used a drug or other substance right before school or during school or work hours was also gathered. Additional questions on whether the respondent ever sold drugs are described in Crime, Delinquency & Arrest. Drug use questions were not asked in rounds 16 or 18-20.