BACKGROUND AND AIMS: Long-term harms of cannabis may be exacerbated in adolescence, but little is known about the acute effects of cannabis in adolescents. We aimed to: (1) compare the acute effects of cannabis in adolescent and adult cannabis users, and (2) determine if cannabidiol (CBD) acutely modulates the effects of delta-9-tetrahydocannabinol (THC).

DESIGN: Randomised, double-blind, placebo-controlled, crossover experiment. The experiment was registered on ClinicalTrials.gov (NCT04851392). The setting was a laboratory in London, United Kingdom, with twenty-four adolescents (12 women, 16-17 year-olds) and 24 adults (12 women, 26-29 year-olds) who used cannabis 0.5-3 days/week and were matched on cannabis use frequency (mean=1.5 days/week).

INTERVENTION: We administered three weight-adjusted vaporised cannabis flower preparations: 'THC' (8mg THC for 75kg person); 'THC+CBD' (8mg THC and 24mg CBD for 75kg person); and 'PLA' (matched placebo).

MEASUREMENTS: Primary outcomes were: i) subjective 'feel drug effect'; (ii) verbal episodic memory (delayed prose recall); and (iii) psychotomimetic effect (Psychotomimetic States Inventory).

FINDINGS: Compared with 'PLA', 'THC' and 'THC+CBD' significantly (p<0.001) increased 'feel drug effect' (mean difference (MD)=6.3), impaired verbal memory (MD=-2.7), and increased psychotomimetic effects (MD=7.8). There was no evidence that adolescents differed from adults in their responses to cannabis (interaction p≥0.4). Bayesian analyses supported equivalent effects of cannabis in adolescents and adults (BF >3). There was no evidence that CBD significantly modulated the acute effects of THC.

CONCLUSIONS: Adolescent cannabis users are neither more resilient nor more vulnerable than adult cannabis users to the acute psychotomimetic, memory-impairing, or subjective effects of cannabis. Furthermore, in adolescents and adults, vaporised cannabidiol does not mitigate the acute harms caused by delta-9-tetrahydocannabinol.