OBJECTIVE : As part of cannabis legalization in Canada and several US states, regulations specify how THC levels should be labelled on products; however, there is little evidence on the extent to which consumers understand and use THC labelling to inform consumption amounts. The current study was designed to assess comprehension of cannabis-related information including communication of dose and strength of product on different labelling designs among young Canadians. METHODS : Two experiments were conducted in October 2017 among Canadian youth and young adults aged 16-30 years as part of an online cross-sectional survey (N = 870). Experiment 1 randomized respondents 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 (7.4 %) and THC mg condition (13.4 %). When cannabis products were labelled using a traffic light system, participants were more likely to identify THC level: low THC (85.1 %) or high THC (86.4 %) than the control condition (2.0 % and 5.2 % respectively). CONCLUSIONS : 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.