Fifteen adult chronic heavy marijuana smokers who had smoked at least 3,000 joints in their lifetime, and who smoked at least four of the last seven days and tested positive for urinary cannabinoids and fifteen non-marijuana smoking control subjects who were age, sex and education matched were included in the study (see Table 1). Subjects were recruited from the greater Boston area, with participants from both downtown and suburban locations included. Recruitment sites included local colleges and universities, sports clubs and athletic centers, supermarkets, community centers and other public locations. All subjects received the Structured Clinical Interview for DSM-IV (SCID-P) (First et al., 1995) to ensure that no Axis I pathology was present (except for marijuana abuse, a requirement for the marijuana smoking group) and had no history of head trauma or medical condition. No subjects met diagnostic criteria for current or previous alcohol abuse or dependence; subjects were excluded if they reported more than 5 lifetime episodes of using any category of illicit drugs (including sedative-hypnotics, stimulants, cocaine, opioids, hallucinogens, and MDMA) except for marijuana in the case of
