Marijuana and Alcohol Combine to Affect Driving Performance

The February 5, 2021 issue of Psychopharmacology published data from a Canadian study assessing the effect of both THC and alcohol on driving performance.

Regular users of cannabis participated in simulated driving sessions after smoking marijuana (12.5% THC) and drinking alcohol (target breath alcohol 0.08%).

Researchers discovered the driving performance after ingesting both marijuana and alcohol “was significantly greater than the effect of each drug by itself.”  This included the test subjects’ reaction time as well as their ability to maintain speed and lateral position. 

The suggested additive effect of marijuana and alcohol on driving performance is consistent with prior research in this area.

Iowa law does not prohibit drinking and driving.  Instead, the state’s OWI law targets operating with breath alcohol concentration over 0.08 percent or while under the influence of alcohol.

Adding marijuana to the mix only serves to amplify the sort of driving behavior for which police are already on the lookout: weaving, crossing the center line, fluctuating speed and delayed reaction time.  That is probably reason enough to stay off the road because poor driving like this will inevitably lead to a 911 call from other motorists.

Plus, any amount of even non-impairing marijuana metabolites present in a urine or blood sample constitutes OWI in Iowa.  Again, the backdoor prohibition against cannabis as frequent readers of the GRL Law blog are well aware.

What’s the takeaway here?  Don’t take any chances with both cannabis and alcohol on board.  Play it safe.  Call an Uber.