A study involving 134 cannabis users aged 16-23 has found that when they were smoking cannabis containing a low percentage of cannabidiol they performed much worse on the memory tests. In contrast, those smoking cannabis high in cannabidiol performed just as well on the tests when they were intoxicated as when they were sober. There were no differences in the THC content of the cannabis smoked by any of the participants (THC is the main psychoactive ingredient, which gives the characteristic ‘stoned’ feeling, and feelings of paranoia).
For the study, the participants were tested on two separate occasions — once while they were smoking their own preferred type of cannabis and were intoxicated, and once when they had not smoked for the last 24 hours and were sober.
Levels of cannabidiol in cannabis can range from virtually none to 40%. This study suggests that cannabidiol can counteract the memory-impairing effects of THC. Unfortunately, low-cannabidiol strains (like skunk) now dominate the market of street cannabis, suggesting current users will be more at risk of cognitive impairment.
(2010). Impact of cannabidiol on the acute memory and psychotomimetic effects of smoked cannabis: naturalistic study.
The British Journal of Psychiatry. 197(4), 285 - 290.