Does Acute THC Reduce Effort for Rewards? Why That Is Not a Diagnosis of Chronic Apathy

Oral THC reduced willingness to choose a demanding reward task in a controlled study of women. The result concerns an acute decision under experimental conditions, not proof of a permanent “amotivational syndrome.”

The choice being tested

Wardle and colleagues analyzed a double-blind, counterbalanced comparison of oral THC and placebo in young women with prior cannabis experience who were not regular users. Participants repeatedly chose between easier and harder tasks with different reward amounts and probabilities.

This was a secondary analysis within a larger study. The pandemic abbreviated the dosing schedule for some participants, so not everyone completed all dose conditions.

Choice and movement speed were separated

THC reduced hard-task choices, particularly at moderate to high expected reward values. The higher dose differed significantly from placebo; the lower dose did not clearly differ from either comparison condition.

THC also slowed performance, but the choice effect remained after statistical adjustment for psychomotor slowing. The analysis therefore did not simply equate slower button pressing with lower motivation.

What the experiment cannot establish

The task does not reproduce every reason someone works, studies, cares for family, or pursues a goal. Results from a selected group of young women do not automatically generalize to men, older adults, or highly tolerant users.

The study did not establish long-term changes after cannabis cessation, a diagnosis of apathy, or an individual’s intent in a real event. A careful opinion distinguishes acute effort-based decision-making from enduring personality, clinical illness, and social judgments about cannabis users.

The oral doses were placebo, 7.5 mg THC, and 15 mg THC. Forty participants completed all three sessions; the paper reports another 18 with the abbreviated placebo/high-dose schedule. The dose-specific comparisons are more informative than a broad assertion that any cannabis exposure necessarily eliminates motivation.

Related reading: task-specific cognitive findings after cannabis.

Primary research

Margaret C. Wardle; Elisa Pabon; Heather E. Webber; Harriet de Wit. Delta-9-tetrahydrocannabinol reduces willingness to exert effort in women. Psychopharmacology (2022). DOI: 10.1007/s00213-021-06032-1.