Eligible participants attended a baseline session, before which they were instructed to abstain from alcohol and marijuana for 6 h and from caffeine and nicotine for 1 h. After reading and signing an informed consent form, participants gave a saliva sample, for DNA analysis, and Breathalyzer and urine samples, to ensure they had abstained from alcohol, had recently used marijuana, and had not used any other substances. All participants tested positive for Δ9-THC metabolites, but negative for metabolites of other drugs. Participants completed the Marijuana Withdrawal Checklist (MWC), Marijuana Craving Questionnaire (MCQ), and Profile of Mood States (POMS; see below for descriptions of these measures), and were then scheduled to return in 24 h. They were instructed to abstain from marijuana and alcohol between the two sessions and from caffeine and nicotine for 1 h prior to the second session and were informed that another toxicology screen would be performed to confirm their abstinence.
