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Does THC Cause Psychosis?

One of the most persistent controversies around cannabis use relates to its effect on the risk of psychiatric disorders, particularly psychotic disorders. There has been a school of thought that proposes high-THC content cannabis can possibly trigger psychosis due to its psychotomimetic effect.

The current research situation around cannabis and psychosis is quite well developed, but more evidence is still needed to confirm the attendant mechanisms.

The numerous studies that have been conducted based on the tentative assumption that cannabis use might cause an increased risk for psychosis have not provided us with either a better insight into how the plant actually produces this effect, or with an effective method for reducing the risk of psychosis.

Whilst overall cannabis might have a higher average THC content than 30 years ago, we still know that high-THC content cannabis was in circulation at that point in time. Moreover, whilst cannabis usage and potency has increased, it appears that the incidence of psychosis in the overall population has not (Di-Forti et. al. 2009). However, the complexities of epidemiological studies mean that a causal relationship is difficult to establish.

In fact, several psychiatrists have put forward the theory that cannabis cessation might be implicated in the prevalence of psychosis in cannabis using populations, in particular for people with substance use disorders (Schoeler et. al. 2016).

Schwarcz et. al. (2010) report on a case-series of 6 patients with psychosis who tried dronabinol during their treatment periods. Dosages investigated were 10-30mg/day (split into two daily intakes) and significant improvement in various psychiatric measures for 4/6 individuals in this small cohort of psychosis patients was observed. They suggest that future studies researching this topic use patients who have previously benefited from consuming cannabis, as some patients don’t respond well, so individual case-histories are extremely important to consider.

Gerlach et. al. (2019) conducted a review of psychosis and cannabis use along with reporting a case series. They put forward the view that cannabis use and psychotic episodes have a complicated link, for some patients the adverse effects of cannabis wane when the drug is stopped and for others it continues or worsens. Importantly, individual case histories were important and treatments of psychosis centered around IV benzodiazepines, mood stabilisers and atypical antipsychotics.

Colizzi et. al. (2019) investigated a small group of healthy human volunteers using IV d-9-THC in order to look at the psychological effects. They tested IV d-9-THC and compared this against placebo and found that IV-THC increased the chances of negative reactions. More research is needed on IV cannabinoids especially as IV administration of cannabinoids is a medical application with limited knowledge and therefore requires more research.

Minichino et. al. (2019) conducted a review of translational endocannabinoid system and psychosis studies and found there was a significant increase in measured Anandamide and ECS tone in patients compared with controls. However, it should be noted that there was a great degree of variability in the analytical methods used for the studies and the types of samples used (such as CSF and blood plasma). The authors suggest better standardised methods for future research is an important priority.

Bioque et. al. (2019) investigated gene-environment interaction related to the endocannabinoid system, in particular the allele related to the gene encoding Fatty-Acid-Amide-Hydrolase (FAAH). For people with certain EC biology they appear react to cannabis differently, possibly increasing the risk of psychosis. This is complex and involves gene-environment interaction which the authors demonstrate in a small sample of first-episode psychosis patients.

The association between cannabis use and chronic psychosis (including schizophrenia diagnosis) is stronger in those individuals who have had heavy or frequent cannabis use during adolescence or in those who used cannabis with high THC potency.

While there are some correlations between these factors and psychosis, studies that examine whether certain patterns of substance use and other problem behaviours are more predictive of psychosis, or of major depressive or bipolar disorders, might provide interesting insight, as could genetic or familial studies that examine shared risks for these different problem behaviours and mental disorders.

For more information on these studies and the treatment of schizophrenia using medical cannabis, take a look at our evidence base, a ground-breaking systematic review of the history of research in this area and a global first-of-its-kind searchable database for clinical referencing.

As always, like with any other patients, those with schizophrenia should only proactively seek to use medical cannabis products after a close consultation with and careful assessment from an experienced medical practitioner.

Further investigation and research into cannabis use (both recreational and medical) is thoroughly encouraged by The Academy, particularly through the use of our own online coursesevidence base and whitepapers.

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