Persistent THC Tolerance in Primates Was Different From a Baseline Attention Deficit
Primates exposed to THC during adolescence were less sensitive to later THC challenges approximately a year after chronic dosing ended. Their baseline attention performance did not show the same group differences. Persistent tolerance and persistent sober impairment are different propositions.
A small longitudinal animal experiment
Twelve squirrel monkeys received vehicle, low-dose THC or high-dose THC during adolescence, four per group. Chronic treatment lasted six months. As adults after an extended interval, they learned a touchscreen vigilance task and received acute THC by oral and intramuscular routes.
The challenge revealed the difference
Groups reached comparable stable task performance before the acute challenges. Larger THC doses were needed to disrupt vigilance in animals with prior chronic THC exposure. Both administration routes showed dose-related effects, although potency and onset differed.
What the experiment did not resolve
The study focused on attention, not a complete cognitive battery. The small sample and unequal sex distribution limited precision, particularly for sex comparisons. Repeated adult challenges also complicate extending this design to many further tasks, because new exposure could add new tolerance.
Do not equate persistence with a proven mechanism
Lasting neural changes were discussed as possible explanations, but this experiment did not establish an irreversible mechanism. Nor did it show that adolescent cannabis exposure improves adult functioning. It identified altered sensitivity to a later drug challenge in an animal model. The distinction between baseline performance and challenge response must be retained before applying the result to human development, treatment or an individual forensic assessment.
Related analysis: evaluating cannabis tolerance claims.
Primary research
Razavi Y; Kohut SJ; Bergman J; Kangas BD. Chronic Δ9-tetrahydrocannabinol exposure during adolescence is associated with persistent behavioural tolerance in adult nonhuman primates. British journal of pharmacology (2025). DOI: 10.1111/bph.70179.
