Driving under the influence of marijuana

Dr Derrick Aarons MD, PhD:  

Ganja has been used historically in our society for both recreation as well as religious purposes.

However, in recent years, research has indicated that certain health benefits may be derived from some specific chemicals present in the plant. This has led to the term medical marijuana in the USA and medical cannabis in Canada.

As with allopathic medicine and pharmaceutical products, however, there are often side effects and unwanted consequences to consider. One such consequence is that many people drive motor vehicles while under the influence of marijuana/ganja. While no statistics are available for Jamaica, in the USA, marijuana has been prescribed for some patients with chronic pain and individuals have simultaneously been engaging in risky behaviour, driving under the influence and thereby putting both themselves and other motorists on the road at risk.


In a study of nearly 800 people who were prescribed medical marijuana, more than half of them reported driving within two hours of its use. Some reported driving while “a little high”, and about 20 per cent reported driving “while very high”.

The research, conducted by the University of Michigan Addiction Center at its School of Medicine in Ann Arbor, USA, was published in the January edition of the journal Drug and Alcohol Dependence.

Participants in the study were 21 years and older, and were seeking certification or recertification for medical marijuana. The mean age was 46 years, with 52 per cent being men, and 81 per cent being Caucasians.

Most of the participants were unemployed (61 per cent), and 32 per cent were receiving disability benefits in the USA.

Questions included the number of hours “high” per day, and the average quantity of marijuana used per week over the previous month.

Individuals were also asked the number of times within the previous six months that they drove “within two hours of using marijuana”, “while a little high on marijuana”, or “while very high on marijuana”. Possible responses ranged from “never” to “more than 10 times”.

The majority

Nearly three quarters (73 per cent) of participants reported using marijuana daily or almost daily over the previous six months. Fifty-six per cent drove within two hours of marijuana use, 51 per cent drove while “a little high”, and 21 per cent drove while “very high”.

Age also played a factor, with younger adults being at greater risk for driving under the influence of cannabis (DUIC).

The researchers had much concern since not only did people drive while a little high or “really high”, but disappointingly, some of them did so frequently. Further, due to the high frequency of use, individuals who take medical cannabis are at particularly high risk for driving under the influence.


Another research meta-analysis (analysis of the findings from several research studies) published in 2016 similarly called attention to the public health risks associated with driving under the influence of cannabis, including a potential increase in motor vehicle accidents.

However, the rapidly shifting policies on marijuana/cannabis use has now drawn even greater attention to this very important public health issue.

Consequently, there is an urgent need to better understand driving under the influence of cannabis in order to fully inform future prevention efforts. In locations where medical marijuana is prescribed, or in similar pertinent settings, individuals should be counselled about the risks of getting behind the wheel of a motor vehicle after they use marijuana. This is critical as people may be unaware they could experience impaired reaction times, including being unable to react to the unexpected on our roads while driving.

Risk counselling

Risk counselling is particularly important since, unlike other prescription medicines and products, medical marijuana does not carry a warning label. Further research is critical, however, since science still does not have a large body of evidence regarding public health risks associated with medical marijuana, and how much (dose) affects a particular person, or how the way a person uses it may affect them.

The best guide therefore is to advise that individuals should avoid driving within two hours of using marijuana, and should get a ride from someone else if they need to change their location. Further, future research is needed to find out the recommended standard ‘dose’ of medical cannabis across the various conditions for which it is used.

Research into driving records and motor vehicle accident data would also be advantageous.

Further studies in ‘outcomes’ and what happens to people over a couple of years while they are using medical marijuana would also be very informative to guide us in the future. The health of the general public (public health) matters!

Dr Derrick Aarons MD, PhD, is a consultant bioethicist and family physician; a specialist in ethical issues in health care, research, and the life sciences; the health registrar and head of the health secretariat for the Turks and Caicos Islands, and a member of UNESCO’s International Bioethics Committee (IBC).

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