Heavy Cannabis Users: Subjective High and Psychomotor Tests Did Not Move Together
Heavy cannabis users can report a substantial high while showing comparatively modest changes on selected psychomotor tests. That dissociation does not establish unimpaired driving or a universal tolerance exemption.
What the experiment measured
Ten chronic cannabis smokers completed controlled smoking sessions with serial whole-blood THC measurements and subjective, physiological and psychomotor assessments. Nine participants were men. The study involved a specified cigarette, rather than today’s entire range of cannabis products.
The researchers compared the timing of reported effects with concentrations collected at the same assessment points. Whole blood was the stated matrix; those values should not be substituted with plasma concentrations from unrelated experiments.
Positive and null responses coexisted
Smoking significantly increased ratings including high, good drug effect, stoned and sedation. Anxiety and restlessness did not significantly change. The authors characterized psychomotor changes as modest relative to the robust subjective and cardiovascular responses.
A null anxiety rating therefore did not mean no intoxication, and a modest task effect did not erase a strong reported high. Different endpoints capture different aspects of response.
Timing complicated the concentration relationship
Blood THC declined rapidly while subjective effects persisted. Mean concentration–effect plots formed counterclockwise hysteresis loops, and individual plots varied substantially.
The same concentration on different portions of a time course can therefore coexist with different effects. A group-average loop does not provide an exact individual reconstruction of time since smoking or functional condition.
How far tolerance evidence travels
The small, selected group limits generalization to occasional users, women and other dosing patterns. Selected laboratory tasks are not equivalent to a complete on-road assessment or collision-risk estimate.
The study supports separating use history, subjective experience, task performance and measured concentration. It does not establish that heavy users are always unaffected, or that subjective high alone supplies an objective measure of every ability relevant to driving.
For context, see our discussion of THC concentrations and the separate question of impairment.
Primary research
David M. Schwope and colleagues. Psychomotor Performance, Subjective and Physiological Effects and Whole Blood Δ9-Tetrahydrocannabinol Concentrations in Heavy, Chronic Cannabis Smokers Following Acute Smoked Cannabis. Journal of Analytical Toxicology (2012). DOI: 10.1093/jat/bks044.
