Acute effects of orally administered Δ8-THC and Δ9-THC on simulated driving ability, cognitive performance, and subjective drug effects

∆8-Tetrahydrocannabinol (∆8-THC), a structural isomer of ∆9-THC, is a growing drug of concern often marketed as a “milder” alternative to ∆9-THC. No controlled studies have evaluated doses above 40mg ∆8-THC or examined its acute effects on driving. Healthy adults (N=20) with no past 30-day cannabinoid use completed four double-blind, outpatient drug administration sessions, self-administering oral doses of ∆8-THC (30mg, 60mg), ∆9-THC (30mg), or placebo. Simulated driving was assessed at baseline and at 2 hrs post-dosing. The primary outcome Global Drive Score (GDS), a composite measure of driving performance, and secondary driving outcomes were examined. Subjective drug effects, cognitive and psychomotor performance, vital signs, and whole blood cannabinoid concentrations were assessed at baseline and over 8 hrs post-administration. ∆8-THC and ∆9-THC significantly impaired driving relative to placebo with decrements in coherence during the car following and poor maintenance of lane positioning. 30mg ∆9-THC produced the greatest impairment but was not significantly different from 60mg ∆8-THC. Subjective effects generally peaked between 2-3 hrs post-dosing. ∆8-THC produced effects that were qualitatively similar to ∆9-THC, but at approximately half the potency on most outcomes. ∆8-THC significantly impaired driving performance, notable given its widespread availability and common perception as less psychoactive than ∆9-THC. At the same dose, ∆8-THC produced similar types of impairment and physiological effects, but at a lower magnitude than ∆9-THC, likely driven, in part, by higher concentrations of the psychoactive 11-OH metabolite following ∆9-THC relative to ∆8-THC administration. These findings can inform ∆8-THC policy and public safety initiatives that deter drugged-driving.