Most respondents had either a university degree or a trade/vocational certificate and were engaged in either full time or part time employment . The most frequently reported primary condition being treated with cannabis was pain , followed by mental health conditions and sleep-related conditions . Inhalation was the most common route of administration . Only a small number of respondents accessed legal medical cannabis with a prescription, with most respondents sourcing their medical cannabis from an illicit dealer , from friends or family or by growing their own . With regard to the type of cannabis mainly used, 21.5% reported THC-dominant or THC only, 18% reported approximately equal amounts of THC and CBD, 12.5% reported CBD-dominant or CBD only, and 48% indicated that it varied between batches or that they did not know. The mean duration of time until respondents felt no effect after using medical cannabis was 219 min , 253 min , 294 min and 210 min . Fig. 1 shows responses to several statements regarding driving related behaviours. Most respondents agreed or strongly agreed that they felt confident in their capacity to accurately assess their driving ability after consuming medical cannabis. A similar percentage agreed or strongly agreed that their medical cannabis use does not impair their driving. A majority felt they tended to drive more carefully following use of medical cannabis and most denied that cannabis affected reaction time, focus, speeding, drifting out of lane or risk taking. Just under half agreed or strongly agreed that they tended to leave a larger gap between them and the car ahead after using medical cannabis. There was less certainty from respondents around whether they felt more in control of their vehicle . Fig. 2a shows the duration of time that respondents typically wait before driving after using medical cannabis relative to primary route of administration. Overall, more than a third of respondents reported driving within 3 hours of using medical cannabis; 11.9% waited 4-6 hours and 25.9% waited 7-12 hours, while 27.5% waited at least 12 hours. Fig. 2b shows the length of time until respondents feel no effects after using medical cannabis. Most said 1-3 hours ; 27.8% said 4-6 hours while 8.8% said 4-6 hours and 0.9% said 13-24 hours.
Patients using oral products tended to report a longer duration of action when compared with smoked or vaporized cannabis. From the above, most respondents were estimated to be unlikely to drive while under the influence of cannabis; this proportion was slightly higher for inhaled routes of administration than for oral routes . This proportion was also higher for THC-dominant products and THC/CBD-equivalent products than for CBD-dominant products . Only a minority of respondents had been subjected to roadside drug testing , with very few respondents having ever been convicted of DUIC . Most respondents indicated that the presence of roadside drug testing deterred them from driving after using medical cannabis. Table 2 shows the results of two binary logistic regression models that assessed the relationship between respondent characteristics and DUIC behaviours. In the first model, there was a strong association between frequency of cannabis use and respondents’ belief in whether medical cannabis impairs their driving. Specifically,trimming tray respondents were 3.1% more likely to think that their cannabis use does not impair their driving for each additional day of cannabis use . Respondents’ confidence in their capacity to assess their own driving ability after using medical cannabis was strongly related to their belief in whether medical cannabis impairs their driving, with those who were confident being far more likely than those who were not confident to report that their medical cannabis use does not impair their driving . Respondents who were not deterred by the presence of roadside drug testing were also more likely to think that cannabis does not impair their driving In the second model, estimated likelihood of DUIC was strongly associated with employment status, with those who unemployed being significantly more likely to engage in DUIC relative to those who were engaged in full time or part time work . Frequency of use was also related to likelihood of meeting criteria for DUIC, with a 2.7% increase in odds for each additional day of cannabis use . There was a marginal decrease in DUIC likelihood for each percentage increase in proportion of total cannabis use that was medical . Respondents who were confident they could accurately assess their driving ability were far more likely to engage in DUIC than those who were not confident. Respondents who were not deterred by the presence of roadside drug testing were almost 3 times as likely to engage in DUIC relative to those who were deterred .The present study was designed to assess driving-related behaviours and attitudes among a convenience sample of Australian medical cannabis users recruited as part of our larger CAMS-18 survey. The term ‘medical cannabis’ was used to refer to any use of a cannabinoid product to treat or alleviate symptoms arising from a self-reported medical condition. These were in some ways an unusual medical cannabis patient group by international standards: the relatively slow roll out of official legal medical cannabis in Australia meant that the vast majority of respondents were still self-medicating with illegal products using inhaled routes of administration.
This user profile is likely to change as the official access scheme, which is dominated by orally delivered THC and CBD containing products, converts more patients from illegal to legal access. A key finding of the current study is that a substantial proportion of medical cannabis users are driving shortly after using cannabis, with some driving during the time of peak effects when impairment tends to be greatest. More than 19.0% of users reporting driving within one hour of consuming cannabis and 34.6% of all users within 3 hours of use . By comparison, 56.4% of medical cannabis users in Michigan with chronic pain drove within 2 hours of consuming cannabis. In other surveys, 9.3% of older drivers in Colorado reported driving within one hour of cannabis use, and 13.2% of Canadian non-medical cannabis users reported driving within two hours of use. While it is important to note that most respondents in the present survey reported waiting at least 7 hours before driving, with 25.9% waiting 7-12 hours, and 27.5% waiting at least 12 hours, the relatively high incidence of driving shortly after using cannabis is concerning. This suggests a need for public information campaigns that educate medical cannabis users around the risks associated with DUIC. Existing public health guidelines, such as Canada’s Lower Risk Cannabis Use Guidelines , recommend that medical cannabis patients wait at least 6 hours before driving after using cannabis. However, as other jurisdictions consider establishing similar guidelines, it is important to consider that the duration and magnitude of cannabis effects may vary with factors such as gender, body mass and consumption of alcohol and may in some cases exceed 6 hours. For example, alcohol and cannabis produce additive effects that may exacerbate and prolong driving impairment. Conversely, the magnitude and duration of cannabis effects may be decreased with increased frequency of cannabis use, most likely due to tolerance, and with use of CBD-dominant or low THC products. Further research is needed to elucidate the extent to which these factors impact the driving impairment produced by cannabis and to guide public policy in this area. It is somewhat surprising that more than 1 in 3 respondents drove within 3 hours of cannabis use given that Australia is one of the few jurisdictions in the world to have extensive, random roadside drug testing for THC in oral fluid. In our recent study, most participants tested positive for oral fluid THC at 10 min after vaporization of cannabis containing predominantly THC or equivalent amounts of THC and CBD, with some testing positive at 3 hours . Despite the relatively high prevalence of driving shortly after cannabis use, a large proportion of respondents did say that the presence of roadside drug testing deterred them from driving after using medical cannabis. Only a small minority of the overall cohort had been subjected to such testing at the time of the survey, however, with an even smaller proportion indicating they had ever been convicted of DUIC. It is interesting to note that those who were not deterred from driving after using cannabis by the presence of roadside drug testing were more likely to think that cannabis does not impair their driving and more likely to engage in DUIC. The finding that 71.9% of respondents felt that their medical cannabis use does not impair their driving is consistent with previous reports showing that cannabis users tend to perceive DUIC as relatively low risk, especially when compared with alcohol . This may support the idea that cannabis users tend to show a comparative optimism bias toward thinking that that their own driving is less impaired and their accident risk lower after using cannabis relative to other cannabis users .
Indeed, in a random survey of weekend night-time drivers in California, only 1 out of 21 drivers who reported using cannabis in the past 2 hours and tested positive for THC agreed that they had taken a drug that impaired their driving. Most respondents in the current study reported that they drive more carefully and take fewer risks after consuming cannabis. Respondents did not agree that cannabis impaired their focus, reaction time or ability to stick to the speed limit. While experimental studies with non-medical cannabis users often find that respondents drive more slowly and leave a larger gap to the vehicle ahead after consuming cannabis, less than half of respondents in the present study said they tended to leave larger gap between them and the car ahead. Similarly, while studies with healthy volunteers show that cannabis can impair lateral control and increase lane weaving, particularly in the first hour and up to 3.5 hours after vaporising or smoking cannabis, most respondents denied drifting out of their lane more frequently after using medical cannabis. It is unclear whether these disparities reflect a high degree of tolerance among respondents in the present study or a lack of awareness of actual driving impairment. Logistic regression showed that respondents who were confident they could assess their driving ability after using medical cannabis were far more likely to deny impairment and to engage in DUIC relative to those who were not confident, irrespective of age or gender. Some evidence shows a poor relation between perceived and actual driving ability in both older and younger drivers and in occasional cannabis users, implying that over-confidence in driving ability after using cannabis grow racks is likely to be a risk factor for DUIC behaviours. Employment status was also strongly related to estimated likelihood of DUIC, with respondents who were unemployed being more than four times as likely to engage in DUIC relative to those who were employed.
While this may reflect greater daytime use of cannabis in this population which in turn may be due to the severity of the underlying condition for which medical cannabis is being used, it is important to note that only a small proportion of respondents were unemployed. This possible explanation should therefore be treated with caution. Frequency of cannabis use was also strongly related to likelihood of DUIC; while the increase in odds was relatively small, a recent study likewise found that frequency of cannabis use was positively associated with the incidence of DUIC, as was the level of intoxication that respondents deemed safe for driving. This is perhaps unsurprising, as those individuals who are using cannabis more frequently will be inherently more likely to drive when having recently using cannabis. Despite the growing use of cannabis for medical purposes, there have been no studies to date that have investigated the acute and/or chronic effects of medical cannabis use on driving. In a recent review, Celius et al. found that most patients with multiple sclerosis-related spasticity who were being treated with nabiximols actually showed an improvement in driving ability, most likely due to a reduction in spasticity and/or improved cognitive function. This finding lends support to the idea that treating medical conditions that might otherwise impair driving with medical cannabis could conceivably have a positive, or at least neutral, effect on driving performance.