All participants were carefully screened with an interview and a medical evaluation to ensure that they fulfilled all study criteria. Further details regarding the inclusion procedure are indicated in Battistella et al (2013). In both groups of cannabis users, we performed a urine and a blood test during the inclusion process in order to determine the concentration of Δ9-Tetrahydrocannabinol-carboxylic acid (THCCOOH) and confirm the regular use and the extent of cannabis consumption (Fabritius et al, 2013b). Participants also filled out a questionnaire about their usual drug use habits. Cannabinoid time profiles in whole blood were determined with the analytical procedures described by Fabritius et al (2013a). Presence of other illicit drugs (cocaine, opiates, and amphetamines) and a positive breath alcohol test were also considered as exclusion criteria.
