A JAMA Network Open study from researchers at Toronto’s Centre for Addiction and Mental Health found that 10-mg and 20-mg THC gummies impaired simulated driving at 2 and 5 hours, even as average peak blood THC levels stayed below the commonly used 5-ng/mL legal cutoff. Clinically, that undercuts blood-level assumptions many patients may make about “safe” driving after edibles and raises policy questions for Canada and U.S. jurisdictions that rely on THC thresholds.

The Move

• In a trial of 40 healthy adults who regularly use cannabis, participants completed four sessions with 0, 2, 10, or 20 mg of THC in soft-chew gummies.

• Driving-simulator testing at 2, 5, and 24 hours found impairment at 2 and 5 hours after 10-mg and 20-mg doses, including worse lane control; the 20-mg dose also slowed reaction time and increased speed variability.

• Average peak blood THC levels were 1.6 ng/mL after 10 mg and 3.4 ng/mL after 20 mg—below the standard 5-ng/mL threshold often used in impaired-driving enforcement, though some individual samples exceeded it.

Why it Matters for Care

• For bedside counseling, the practical message is that patients can remain unsafe to drive for at least 5 hours after edible THC, even if they do not appear profoundly intoxicated and even if a blood test might not cross a legal threshold.

• This is especially relevant in primary care, emergency medicine, addiction medicine, psychiatry, and perioperative settings, where clinicians routinely discuss substance use, safety, and return-to-activity decisions.

• Patients in the study did report lower willingness to drive and less confidence in their driving, but subjective insight is not a reliable substitute for clear counseling on delayed onset and prolonged impairment.

Between the Lines

• The policy friction is pharmacokinetic: edible THC is absorbed more slowly through the GI tract, so impairment may persist while blood concentrations remain comparatively low.

• That contrasts with inhaled cannabis, where the same research team previously found similar impairment alongside average peak THC levels of 30.3 ng/mL—nearly 10 times higher than after 20-mg edibles.

• For lawmakers and law enforcement, the study complicates per se THC-limit frameworks and strengthens the case for performance-based or alternative roadside impairment tools.

What to Watch

• Whether Canadian and U.S. regulators revisit THC-threshold enforcement policies as edible use grows.

• Whether future studies test occasional users, real-world driving, and dose-response effects beyond 24 hours, since this trial involved regular cannabis users and simulator-based assessment.

• Whether clinician guidance, public-health messaging, and product labeling shift toward more explicit wait-time recommendations after edible THC use.

Source: Fox News