Drinking before driving is not recommended. Neither is using cannabis. Now, to the surprise of hopefully very few, research confirms what we already suspected: For drivers, using both is worse than either alone.
A new study from the Johns Hopkins Medicine University School of Medicine found that not only do cannabis edibles combined with alcohol greatly impair driving, but the impairment is also more difficult to detect by standard field sobriety tests.
Because adding cannabis into the mix adds to the impairment from alcohol, researchers worry the legal intoxication limit of .08% breath alcohol level might not suffice when the second drug is involved. It’s not just an additive effect, they emphasize — it’s “synergistic.”
Researchers recruited adults between the ages of 21 and 55 for the study. During outpatient study sessions, they were given a brownie: one with THC, and one without. They also received an alcoholic drink or a placebo drink, and alcohol doses were adjusted per individual to produce a BAC of .05% or .08%.
Notably, participants had previous experience using both substances together in the past year, and had also reported binge drinking in the previous 90 days. Driving was tested via a simulator. Participants each underwent seven sessions, consuming cannabis alone, alcohol alone and both together. There were also placebo versions.
Combining the edibles with alcohol produced effects that were more severe … and lasted longer. People also felt more intoxicated when they consumed both substances together. Researchers hope the study spurs further research and attention from policymakers and public health officials.
And as usual, the best way to drive is sober.