Respondents were participants in the National Epidemiologic Survey of Alcohol and Related Conditions (NESARC), a nationally representative United States sample of 43,093 civilian non-institutionalized participants aged 18 and older. The sampling frame is detailed elsewhere. 28,29 The research protocol, including informed consent procedures, received full ethical review and approval from the U.S. Census Bureau and U.S. Office of Management and Budget. The National Institute on Alcohol Abuse and Alcoholism (NIAAA) sponsored the study, conducted in 2001–2002 by the U.S. Bureau of the Census. Young adults, Hispanics, and African-Americans were oversampled. The overall response rate was 81%. Data were adjusted for oversampling and nonresponse. The sample was then weighted to reflect the U.S. population from the 2000 Decennial Census. We included NESARC participants that used cannabis ≥3 times/week during their period of heaviest use. We further analyzed the subset of this sample that never drank ≥5 drinks/occasion or used other drugs ≥3 times/week (N=1,119) to ensure that withdrawal symptoms were due to cannabis rather than another substance.
