Smoking potent strains of cannabis, such as skunk, increases the risk of acute memory loss compared with those who smoke other types of the drug, experts warned today.
The warning comes from University College London, UK, after researchers found that varieties of cannabis low in cannabidiol, one of the major constituents of the drug, seriously impaired memory recall.
For their study, published in the October issue of the British Journal of Psychiatry, a series of memory tests on 134 cannabis users aged between 16 and 23 was carried out, once while they smoked their own preferred type of cannabis and were intoxicated, and once when they had not smoked for the last 24 hours and were sober.
Analysis was carried out on a sample of the cannabis each participant smoked on the intoxicated day on the levels of 9-tetrahydrocannabinol (THC), the second major component of the drug, and cannabidiol. Saliva samples were also taken from each participant and tested for the two constituents.
They found that those who had smoked cannabis containing low levels of cannabidiol performed much worse on the memory tests when they were intoxicated than when they were sober.
However, those smoking cannabis high in cannabidiol performed just as well on the tests when they were intoxicated as when they were sober. THC content of the cannabis smoked by all the participants was consistent.
Professor Valerie Curran, from UCL, said: “Over the last 20 years, the constituents of street cannabis have changed, with low-cannabidiol strains like skunk now dominating the market.
“But our study suggests that these strains can increase the risk of cognitive harm. On the back of this study, we believe users should be made aware of the risk of memory impairment from smoking low-cannabidiol strains. They should be encouraged to use strains containing higher levels of cannabidiol instead.”
Morgan CJA, Schafer G, Freeman TP and Curran HV (2010) Impact of cannabidiol on the acute memory and psychomimetic effects of smoked cannabis: naturalistic study, British Journal of Psychiatry, 197:285-290
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