Researchers identify plausible mechanism for cannabis-induced psychosis

A review examining the effects of acute and chronic illicit cannabis use, suggests that plausible mechanisms exist for cannabis-induced psychosis. Cannabis use is associated with dependency and withdrawal syndrome. It is also currently the most commonly abused illicit substance. Cannabis use has been associated with poor outcome in psychotic disorders and there is an increasing body of research relating to cannabis use and brain function. Linszen and Amelsvoort sought to examine and review the question of whether there is a plausible mechanism for cannabis-induced psychosis or brain damage.They found that extensive studies exist on the effects of cannabis on cognitive function in the healthy populations, but that these results are difficult to interpret due to methodological issues. Overall results suggest that delta-9-tetrahydrocannabinol (THC) - the principal psychoactive constituent of exogenous cannabis - can induce memory impairments that mimic memory deficits seen in schizophrenia. More specifically, results show that acute cannabis use leads to dose- and delay-dependent, reversible cognitive impairments. The authors point out that the findings on chronic cannabis use are inconsistent, but that long-term use is associated with a "generalised memory deficit with impaired learning, retention and retrieval on neuropsychological tests". Heavy cannabis use is associated with decreased mental flexibility, increased perseverance, reduced learning and lowered intelligent quotient. Evidence also suggests that these effects continue beyond the intoxication period.Neuroimaging studies focussing on the effects of cannabis exposure are limited; however, existing evidence suggests chronic cannabis users have decreased cerebral blood flow (CBF) in frontal, parietal, temporal, and occipital lobes compared with controls. Acute cannabis intoxication has been shown to lead to an increase in CBF including the frontal cortex and basal ganglia. The authors stated that this might provide a partial explanation for the cognitive deficits observed with chronic cannabis use.With regards to brain anatomy, evidence suggests that frequent cannabis use is not associated with structural changes within the brain as a whole or the hippocampus. The authors concluded that while the majority of people who use cannabis do not develop psychosis, "there seems to be no doubt that cannabis can induce psychosis in a subgroup of people who already are susceptible to developing psychotic symptoms." Furthermore, the authors suggest that the majority of cases of schizophrenia are not caused by cannabis.Reference...