Cannabis labelling and consumer understanding of THC levels and serving sizes.

Background: Cannabis products exist in a wide array of forms and concentrations, with a consistent trend towards higher THC concentrations in North American markets. As part of cannabis legalization in Canada and several US states, regulations specify how THC levels should be labelling on products; however, there is little evidence on the extent to which consumers understand and use THC labelling to inform consumption amounts.

Methods: Two experiments were conducted in October 2017 among Canadian youth and young adults as part of an online cross-sectional survey (N=870). Experiment 1, respondents were randomized to one of three labelling conditions (1=No Label, 2=mgTHC, 3=Doses). Respondents interpreted a recommended serving and number of servings contained in the package. Experiment 2 randomized respondents to one of four labelling conditions communicating THC level (1=No Label, 2=%THC, 3=mgTHC, 4=Traffic Light System). Respondents determined level of THC in the product.

Results: Labelling the number of doses per package was associated with the greatest proportion of correct responses (54.1%) when respondents had to determine a recommended serving compared with the no-label control condition (RR=7.28 95%CI 4.81-11.04) and THC mg condition (RR=4.05 95%CI 2.96-5.54). When product was labelled using a traffic light system, participants were more likely to identify THC level: low THC (RR=43.43 95%CI 16.43-114.79) or high THC (RR=16.71 95%CI 9.61-29.07) than the control condition.

Conclusion: Few consumers can understand and apply quantitative THC labelling; in contrast, THC labels that provide ‘interpretive’ information, such as descriptors, symbols, or references to servings have greater efficacy.