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 .
Cognitive and subjective dose-response effects of acute oral Δ9-tetrahydrocannabinol (THC) in infrequent cannabis users
Abstract Rationale . Although some aspects of memory functions are known to be acutely impaired by Δ9-tetrahydrocannabinol ( Δ9-THC ; the main active constituent of marijuana ) , effects on other aspects of memory are not known and the time course of functional impairments is unclear . Objective . The present study aim ed to detail the acute and residual cognitive effects of Δ9-THC in infrequent cannabis users . Methods . A balanced , double-blind cross-over design was used to compare the effects of 7.5 mg and 15 mg Δ9-THC with matched placebo  in 15 male volunteers . Participants were assessed pre and 1 , 2 , 4 , 6 , 8 , 24 and 48 h post-drug . Results . Δ9-THC 15 mg impaired performance on two explicit memory tasks at the time of peak plasma concentration ( 2 h post-drug ) . At the same time point , performance on an implicit memory task was preserved intact . The higher dose of Δ9-THC result ed in no learning whatsoever occurring over a three-trial selective reminding task at 2 h. Working memory was generally unaffected by Δ9-THC . In several tasks , Δ9-THC increased both speed and error rates , reflecting " riskier " speed-accuracy trade-offs . Subjective effects were also most marked at 2 h but often persisted longer , with participants rating themselves as " stoned " for 8 h. Participants experienced a strong drug effect , liked this effect and , until 4 h , wanted more oral Δ9-THC . No effects of Δ9-THC were found 24 or 48 h following ingestion indicating that the residual effects of oral Δ9-THC are minimal . Conclusions . These data demonstrate that oral Δ9-THC impairs episodic memory and learning in a dose-dependent manner whilst sparing perceptual priming and working memory
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 .