Randomized controlled trials (RCTs) provide the most convincing evidence for clinical questions concerning the efficacy of interventions. When participants in RCTs are characteristically different to those in usual clinical practice, it may be difficult to generalize findings. This study compares profiles taken from a centralized intake process for those presenting with cannabis as their main drug, which were then separated into three categories, (a) those who were offered a specialist assessment for cannabis dependence over the phone but did not attend their appointment, (b) those who presented for their initial appointment, and c) those attending and subsequently recruited into an RCT. To explore whether issues such as severity of cannabis use and co-occurring disorders acted as a barrier to attending treatment or to inclusion in an RCT, we examined basic triage information. Results indicated that there were no statistically significant differences on selected characteristics between groups, suggesting that RCT participants were representative of treatment seekers, and that the filtering that occurs between those who make phone contact with professional services and those who present to treatment are not necessarily due to presence of patient characteristics such as coexisting medical, psychological issues, or severity of their cannabis use.