An Australian survey published in 2023 found that 297 of 1,063 respondents who had driven in the previous year reported driving under the influence of cannabis. That 28% figure describes what people told the researchers. Its denominator is the group of survey respondents who said they had driven, so its meaning depends on who took the survey and how they understood the question. Arkell et al., CAMS-20 driving survey
Depending on whether cannabis was taken orally or inhaled, 49% to 56% of respondents reported that they typically drove within six hours of using medical cannabis. That question concerns time since use. The question about driving under the influence depends on whether the respondent considered themselves to be under the influence. A person could report driving within six hours and still believe they were unimpaired. The survey also found that respondents perceived nonmedical cannabis as more impairing than medical cannabis. Arkell et al.
In the authors’ statistical analysis, respondents who reported inhalation or use of THC-dominant products were more likely to report driving under the influence. Those associations can help researchers decide which groups and products to examine in controlled studies. The survey lacked a standardized dose and a measured driving outcome for those reported trips. Establishing an effect on driving performance would require a study that measures performance under defined exposure conditions. Arkell et al.