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 .
Neurophysiological and subjective profile of marijuana with varying concentrations of cannabinoids
This study investigated the contribution of different cannabinoids to the subjective , behavioral and neurophysiological effects of smoked marijuana . Healthy marijuana users ( 12 men , 11 women ) participated in four sessions . They were r and omly assigned to a low or a high Δ9-tetrahydrocannabinol group ( THC ; 1.8 % versus 3.6 % ) . In the four sessions under blinded conditions subjects smoked marijuana cigarettes containing placebo ( no active cannabinoids ) , or cigarettes containing THC with low or high levels of cannabichromene ( CBC ; 0.1 % versus 0.5 % ) and low or high levels of cannabidiol ( CBD ; 0.2 % versus 1.0 % ) . Dependent measures included subjective reports , measures of cognitive task performance and neurophysiological measures [ electroencephalographic ( EEG ) and event-related potential ( ERP ) ] . Compared to placebo , active THC cigarettes produced expected effects on mood , behavior and brain activity . A decrease in performance , reduction in EEG power and attenuation of ERP components reflecting attentional processes were observed during tests of working memory and episodic memory . Most of these effects were not dose-dependent . Varying the concentrations of CBC and CBD did not change subjects ' responses on any of the outcome measures . These findings are consistent with previous studies indicating that THC and its metabolites are the primary active constituents of marijuana . They also suggest that neurophysiological EEG and ERP measures are useful biomarkers of the effects of THC
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 .