Review of: Robinson T et al, Drug Alcohol Depend 2022;238:109582

Study type: Meta-analysis

Cannabis use is common, but at what point does it negatively impact a person’s life to the degree that they meet DSM-5 criteria for a cannabis use disorder (CUD)? When this threshold is met, not only does a person experience physiological effects such as tolerance and withdrawal, but they may be unable to stop their use despite it interfering with relationships and role obligations such as work and school. Is there a certain frequency of cannabis use above which someone risks developing CUD?

 To gain more insight, researchers carried out a systematic review and meta-analysis to find out how use frequency relates to CUD risk. They reviewed six prospective cohort studies encompassing 40,984 participants between 15 and 30 years old, with follow-ups spanning from 3 to 17 years. Researchers identified distinct user groups—nonusers, annual users, monthly users, weekly users, and daily users—and then quantified the rates of CUD across these groups.

Unsurprisingly, they found that increased frequency of consumption corresponded with heightened CUD risk. Possibly less expected, though, was the degree to which the risk increased and the persistence of the trend at all usage levels. Specifically, relative risk increased from 2.03 for annual users to 4.12 for monthly users, 8.37 for weekly users, and 16.99 for daily users. This means that transitioning up one usage category essentially more than doubles CUD risk across all frequency categories.

To offer a clearer perspective to the public, researchers opted to calculate the absolute risk increase (ARI) as well, which is the overall probability of acquiring CUD. If we assume nonusers have a 0% CUD risk, the ARI was 3.5% for yearly users, 8.0% for monthly users, 16.8% for weekly users, and a staggering 36% for daily users. That means one out of every three daily cannabis users are expected to develop CUD.

Carlat Take
Despite the increasing prevalence of cannabis use, there are no guidelines regarding what can be considered “use in moderation” such as we have for alcohol. This study shows that increasing consumption amplifies CUD risk in a linear fashion, all the way up to one in three daily users developing CUD. We’ll have to wait on future studies to better understand the effects of amount consumed and potency, but in the meantime, counsel your patients to decrease frequency of cannabis use.