Of these , the metabolite produces the greatest psychoactive effects .
Cannabidiol ( CBD ) is not psychoactive but plays a modulating role on cannabis psychoactive effects .
The proportion of 9-THC in plant material is higher ( up to 40 % ) than in other cannabinoids ( up to 9 % ) .
Conclusions Findings reveal that 9-THC contributes the most to cannabis psychoactivity .
Due to lower psychoactive potency and smaller proportions in plant material , other psychoactive cannabinoids have a weak influence on cannabis final effects .
Objective This systematic review aims to summarize current evidence on which naturally present cannabinoids contribute to  cannabis psychoactivity  , considering their reported concentrations and pharmacodynamics in humans .
Comparative studies in man and in laboratory animals on 8 - and 9 -trans-tetrahydrocannabinol.
The pharmacological activity of several doses of △ 8-THC and △ 9-TΗC was studied comparatively using rats ( climbing rope test ) , mice ( catatonia and spontaneous motor activity tests ) and rabbits ( Gayer test ) and also human volunteers ( pulse rate , time discrimination and subjective symptoms ) .  △ 9-TΗC was twice as active as △ 8-THC in rats and mice ; both compounds were equiactive in rabbits . In man △ 9-THC revealed to be nearly twice as active as its isomer . There were no qualitative differences between both drugs neither in man nor in the laboratory animals
Of these , the metabolite produces the greatest psychoactive effects .
Cannabidiol ( CBD ) is not psychoactive but plays a modulating role on cannabis psychoactive effects .
The proportion of 9-THC in plant material is higher ( up to 40 % ) than in other cannabinoids ( up to 9 % ) .
Conclusions Findings reveal that 9-THC contributes the most to cannabis psychoactivity .
Due to lower psychoactive potency and smaller proportions in plant material , other psychoactive cannabinoids have a weak influence on cannabis final effects .
Objective This systematic review aims to summarize current evidence on which naturally present cannabinoids contribute to  cannabis psychoactivity  , considering their reported concentrations and pharmacodynamics in humans .