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 .
Strong increase in total delta‐THC in cannabis preparations sold in Dutch coffee shops
The total concentration of THC has been monitored in cannabis  preparations sold in Dutch coffee shops since 1999 . This annual monitoring was issued by the Ministry of Health after reports of increased potency . The level of the main psychoactive compound , Δ 9 ‐tetrahydrocannabinol ( THC ) , is measured in marijuana and hashish . A comparison is made between imported and Dutch preparations , and between seasons . Sample s of  cannabis preparations from r and omly selected coffee shops were analyzed using gas chromatography ( GC‐FID ) for  THC , CBD  and  CBN  . In 2004 , the average THC level of Dutch home‐grown marijuana ( Nederwiet ) ( 20.4 % THC ) was significantly higher than that of imported marijuana ( 7.0 % THC ) . Hashish derived from Dutch marijuana ( Nederhasj ) contained 39.3 % THC in 2004 , compared with 18.2 % THC in imported hashish . The average THC percentage of Dutch marijuana , Dutch hashish and imported hashish was significantly higher than in previous years . It nearly doubled over 5 years . During this period , the THC percentage in imported marijuana remained unchanged . A higher price had to be paid for cannabis with higher levels of THC . Whether the increase in THC levels causes increased health risks for users can only be concluded when more data are available on adjusted patterns of use , abuse liability , bioavailability and levels of THC in the brain
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 .