Do weed and CBD affect driving ability?

One of the great concerns people have when taking any medication – is how it may impair them. So does weed impair driving. We will review the evidence. Given the public understanding of the dangers of driving under the influence of alcohol – it is important that – as cannabis is legalized and is more accessible – that we be aware of the potential dangers of THC.


A Dutch study.published in  Journal of the American Medical Association in December 2020 set out to answer the question of the ability of THC to affect driving when compared to CBD alone.

While THC is psychoactive (makes you high) CBD does not. CBD usage has grown hugely since legalization of hemp derived products in the 2018 Farm Bill.  With almost 15% of Americans reporting CBD usage for matters such as sleep, anxiety and pain relieve –  the importance of the question cannot be underestimated.

The Study

A sample of 26 healthy men and women (average age 23) were given one of 4 different preparations which were vaped. Each preparation was as follows:

  • 13.75 milligrams of THC
  • 13.75 milligrams of THC/CBD
  • 13.75 milligrams of CBD
  • A placebo
Strains rich with THC, the chemical that produces marijuana’s “high,” cause driving impairment up to 4 hours after vaping, but strains that contain CBD (cannabidiol) and no THC do not, says researcher Johannes Ramaekers, PhD, professor of psychopharmacology and behavioral toxicology at the University of Maastricht in the Netherlands.”The implication for the general public is that the cannabis-induced driving impairment should be acknowledged as a public health risk, while taking into account that impairment may differ between cannabis strains and depends on time [elapsed] after use,” he says.


Results: THC vs. CBD vs Placebo

Those who vaped CBD were found to have similar driving – and as such it was determined that CBD did not impair driving.

However in those who vaped THC there was a significant short-term impairment (lasting up to 4 hours) and similar in impairment to that seen in drivers with a blood alcohol content of 0.05%. (0.05% blood alcohol content is the limit in some states but no higher than 0.08% in the US).


Based on the results it is recommended that if the product used contains THC, users should not drive for at least 4 hours. The doses of CBD tested were low and cannot necessarily be extrapolated to higher doses but given that CBD is not psychoactive – more research is required.

So “Does weed impair driving” – yes and you should be cautious not to drive or use heavy machinery for 4 hours after consumption by vaping or smoking. Probably longer if ingested orally due to the longer time to onset and longer duration of symptoms.