Yes and no. Large doses of marijuana can affect perception and psychomotor performance, changes that could impair driving ability. But in driving studies, marijuana produces little or no car-handling impairment – consistently less than produced by moderate doses of alcohol and many legal medications.
Mixing marijuana and alcohol together amplifies potential risks. Surveys show that when THC is detected in the blood of fatally injured drivers, alcohol is often detected as well.
It is never a good idea to get behind the wheel when intoxicated, even if just from marijuana alone.
For some people, marijuana may play a role in bad driving, but the overall rate of highway accidents does not appear to be significantly affected by marijuana’s widespread use. Also, people who frequently use marijuana appear to develop a tolerance to marijuana’s impairing effects.
Unfortunately, as a result of marijuana’s criminalization, harm prevention measures that exist for alcohol consumption – such as safe use guidelines, formal intoxication levels, designated driver education, and easily accessible information about how alcohol impacts physical and mental functioning – are not widely available for marijuana use.
In states where marijuana is legally controlled and regulated, public education about using marijuana safely, including not driving under the influence, is becoming more readily available.