Have chronic cannabis consumers developed tolerance to the residual effects of recent cannabis use?

Background: There are many potential applications for cannabis-based medications. One important question is whether chronic dosing impacts on safety among individuals regularly taking these medications. In this study we examined the relationship between plasma cannabinoid levels and cognition in a range of domains relevant for everyday behaviours such as driving among a group of people that were chronic consumers of cannabis.

Participants: Dependent cannabis consumers (n=132; 74% male; mean age 35 years) entering a treatment study of nabiximols. Most were daily or near-daily smokers (mean 26 of the previous 28 days) and most had consumed cannabis prior to study entry (59% same day, 29% previous day).

Methods: At study entry, participants completed a battery of tasks assessing domains of processing speed, attention, inhibition, learning and working memory. Study procedures were such that no participants would have acutely consumed cannabis. Plasma cannabinoid levels were assessed as well as interview based measures of cannabis consumption, withdrawal and psychological state.

Results: In this group of long-term, heavy consumers, after controlling for general cognitive functioning, Bayesian analyses demonstrated minimal or nil relationships between plasma cannabinoid levels and cognitive performance. While larger, relationships between plasma and speeded tasks remained of minimal magnitude.

Conclusion: Among chronic, heavy consumers of cannabis, there appears to be no practically meaningful impact of non-acute cannabis consumption on cognitive domains relevant for everyday safety. Further examination of these effects in areas such as simulated complex/extended driving contexts may be beneficial, but these initial results are suggestive of safety for chronic outpatient treatment with cannabinoids.