The group of patients comprised 281 methadone-maintained heroin-dependent individuals (Table 1). Males accounted for 73.7% of this sample. The mean (SD) age of the patients was 36.4 (6.3) years. Most patients reported intravenous (IV) heroin self-administration and non-opioid substance use (Table 1). In regard to these variables, patients were comparable by gender with the only exception of cannabis use: male patients reported regular and/or maladaptive patterns of cannabis use more frequently than female patients. The control group comprised 145 subjects recruited from the general population (128 blood donors and 17 clinical staff). Males accounted for 67.6% (n = 98) of this sample. The mean (SD) age of the control subjects was 35.3 (11.2) years. There were no statistically significant differences with regard to age or gender between the patients and the controls.
