It is a common and dangerous myth that cannabis use does not impact driving ability. This claim is, of course, false. Still, it brings an important issue into the spotlight: how exactly does cannabis impact driving ability?


While recreational cannabis use is legal in California, using cannabis while driving qualifies as being under the influence in the same way as being under the influence of alcohol or medications. Remember, it is illegal to drive while under the influence of any mind-altering substance, be it marijuana or alcohol.

Cannabis use slows a driver’s reactions times. On average, someone driving shortly after using cannabis isabout 25% more likely to be in a crash than sober drivers. That said, this effect is dependent on how high a driver is.

There is some evidence to suggest drivers with a small amount of THC (the active ingredient in cannabis) in their blood drive slower and more cautiously as a means of overcorrecting for their impairment. That cautiousness is not necessarily safer, as driving slower than the speed limit can also be dangerous.

On the other hand, drivers with a high amount of THC in their blood are more likely to have difficulty staying in their lane and reacting to hazards, similar to someone under the influence of alcohol.


Driving under the influence of cannabis, by itself, is dangerous. However, there is a much greater risk when mixing with alcohol, even in small amounts, a practice sometimes referred to as ‘cross-fading.’ Some research suggests that the simultaneous use of both marijuana and alcohol results in much greater impairment, even if the individual dose of either drug would normally have an insignificant impact.

Whether it is one drink or a small amount of THC, using any amount of mind-altering substances prevents you from driving safely. Before getting in the car, make sure you are completely sober and if you are not, consider calling for a ride instead. You just might save someone’s life.

To schedule a free case consultation with an experienced Walnut Creek personal injury attorney from Casper, Meadows, Schwartz & Cook, please do not hesitate to give us a call at (925) 275-5592 or send us an email.