This was not an observational crash study or a survey. Participants completed seven outpatient sessions with controlled edible THC doses and controlled alcohol targets, then completed simulated driving and impairment assessments.

That design matters because it lets readers compare THC alone, alcohol alone, and co-use conditions within the same participants.

The most useful counseling point is straightforward: co-use can make driving impairment worse than either cannabis or alcohol alone.

The study also found that confidence to drive and subjective intoxication often shifted under co-use, which matters because people commonly decide whether to drive based on how impaired they feel.

Standardized field sobriety testing did not consistently identify several conditions where simulated driving showed marked decrements.

That does not mean those conditions were safe. It means impairment detection is more complicated when edible THC and alcohol are combined.

The authors note that the common 0.08% legal alcohol threshold may be too liberal when cannabis has also been used.

Clinically, that supports very conservative advice: if alcohol and THC are both in the picture, the safest driving plan is no driving.

This is a patient-counseling paper as much as a policy paper. Legal cannabis access does not remove the need for driving-risk conversations.

For clinicians, the most practical message is to ask about alcohol and THC together, especially with edibles, delayed onset, and social use settings.

This is one of those studies where the safest clinical message is wonderfully boring: do not mix edible THC and alcohol and then drive.

The more subtle point is detection. A person can be meaningfully impaired in a driving simulator without looking clearly impaired on common roadside clues.

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