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 .
Blunted Psychotomimetic and Amnestic Effects of Δ-9-Tetrahydrocannabinol in Frequent Users of Cannabis
Cannabis is one of the most widely used illicit substances and there is growing interest in the association between cannabis use and psychosis .  Delta-9-Tetrahydrocannabinol ( Δ-9-THC ) the principal active ingredient of cannabis has been shown to induce psychotomimetic and amnestic effects in healthy individuals . Whether people who frequently use cannabis are either protected from or are tolerant to these effects of Δ-9-THC has not been established . In a 3-day , double-blind , r and omized , placebo-controlled study , the dose-related effects of 0 , 2.5 , and 5 mg intravenous Δ-9-THC were studied in 30 frequent users of cannabis and compared to 22 healthy controls . Δ-9-THC ( 1 ) produced transient psychotomimetic effects and perceptual alterations ; ( 2 ) impaired memory and attention ; ( 3 ) increased subjective effects of ‘ high ’ ; ( 4 ) produced tachycardia ; and ( 5 ) increased serum cortisol in both groups . However , relative to controls , frequent users showed blunted responses to the psychotomimetic , perceptual altering , cognitive impairing , anxiogenic , and cortisol increasing effects of Δ-9-THC but not to its euphoric effects . Frequent users also had lower prolactin levels . These data suggest that frequent users of cannabis are either inherently blunted in their response to , and /or develop tolerance to the psychotomimetic , perceptual altering , amnestic , endocrine , and other effects of cannabinoids
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 .