Dr. Grossi's Blog


Dr. Philip Grossi
Tuesday, 02 November 2010

The topic of marijuana is a  timely one considering  that California Proposition 19 (legalization of marijuana) is being voted on today.  People will undoubtedly vote their experience with marijuana or that of their friends or family  which makes the decision for the society at large irrational because one's response to it is determined by one's unique genetic makeup and the balance of various cannabinoids of which there are about 70 unique to the plant.  The balance between Δ-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) is especially important.  The social milieu is undoubtedly also important in producing specific behavioral responses. Therefore, any decision is based on an extraordinarily large number of factors which are unlikely to repeat in anything less than evolutionary time. 

illustration to marijuana blogCannabis is very popular the world over.  Its use has increased dramatically in the past dozen years.  Indeed, the European Monitoring Center for Drugs and Drug Abuse estimated that the number of people seeking treatment for abuse of marijuana has greatly increased since 1999 and represents one in seven referrals for drug abuse treatment.  In healthy individuals there are many studies that document the acute findings of cognitive impairment, anxiety, memory impairment, psychomotor control impairment, and psychotic or psychotic-like symptoms.  Longer term effects remain in question and very few develop dependence or psychosis. 

The main psychoactive ingredient is THC and it is this effect that  many people seek.  When THC is given intravenously to healthy people it produces anxiogenic effects and psychotic-like symptoms.  CBD however has anxiolytic effects, antipsychotic effects, and is thought to be neuroprotective.  In short,  CBD is thought to protect against the THC effects. (THC is a partial agonist at CB1 whereas CBD is an antagonist at CB1 and CB2.)

A recent naturalistic study by Morgan et.al. published in a recent issue of the British Journal of Psychiatry  compared compared 134 cannabis users on measures of memory (prose recall-- considered the best everyday predictor of everyday memory performance) and psychotomimetic symptoms as indexed by the PSI.  What they found was that those that smoked cannabis low in CBD had clear-cut memory impairment whereas those that smoked cannabis with high CBD had no memory impairment in immediate or delayed prose recall.  However, with regard to psychotomimetic effects, CBD did not effect the findings which were that both high and low CBD cannabis smokers showed similar symptoms when acutely intoxicated.  This last represents a null finding as the researchers had predicted that high CBD would reduce psychotomimetic symptoms.

There are several important implications to this study.  First, the current popularity of the skunk (low CBD to THC) type of marijuana will have more adverse cognitive and memory effects. Second, CBD may have a therapeutic role for memory problems especially from THC.  Third, CBD may well be a worthy research molecule for treatment of psychosis and anxiety. The marijuana sold in dispensaries should be labeled with THC and CBD content to allow the consumer to make a more informed decision.


November 3, 2010.  Proposition 19 did not pass.