A new study from the University of York shows that research into the association of psychosis with cannabis focuses almost completely on men users, significantly limiting our knowledge of the drug’s effects on human health.
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In 2016, over 190 million people in the world used cannabis, making it the third most commonly used drug in the world. Cannabis use is linked to certain risks, most notably that of psychosis.
Cannabis psychosis has a tremendous negative impact on both cannabis users and their families. The relationship between cannabis and psychosis has been a bone of contention for a long time among addiction researchers. An accurate understanding of this would help greatly to direct limited health resources towards those at highest risk.
While this association has been known for more than a hundred years, increasing cannabis use in the Western world brought it to the attention of researchers. Andreasson et al. performed a foundational study (in male users) which set the direction for research in this area for decades. They concluded that cannabis independently increased the risk of developing schizophrenia, to 6% of heavy users.
Researchers have not yet been able to determine at what point cannabis-induced psychosis may be diagnosed. Both acute and long-term psychotic reactions occur, which means the statistics vary with place, assessor, and type of evaluation.
Scientists currently favor one of three explanations for the link between cannabis use and schizophrenia. One, cannabis use triggers schizophrenia in some individuals. This is difficult to prove, because cannabis metabolites continue to be excreted in urine for weeks following a single use, which enormously increases the chances of a false diagnosis of cannabis psychosis.
Two, schizophrenics use cannabis to treat their early symptoms. This, however, belies the most common reasons given by the users themselves to explain why they use the drug, namely, pleasure and recreation.
Certain cannabidiols are useful in treating schizophrenia, adding plausibility to the theory. Against this we must set the fact that in recent times the concentration of the potent and pro-psychosis compound Δ9-tetrahydrocannabinol (THC) has risen, relative to the less potent cannabidiols (CBD) in cannabis.
Finally, there are factors which predispose to both schizophrenia and to cannabis use.
Ian Hamilton, the author of the current study, observes that cannabis is being legalized in many countries worldwide, for medical and recreational use. Yet, at the same time, we are possibly missing important information on the topic because of inadequate research.
Most research has concentrated on teasing out genetic and biologic risk factors for cannabis psychosis. This means that we have largely neglected the impact of social and cultural factors which may be just as important.
In the current study, which carried on past work from the same institution, two issues came to the fore.
The first was an obvious lack of female representation in cannabis research. Women cannabis users are simply not present in the vast majority of cannabis studies. Hamilton cites a possible link to the lack of women scientists in the field of addiction research.
The second issue relates to the focus of addiction studies in the developed world. Most researchers in this field have focused on America, Europe and Australia, leaving out vast and populous areas like Africa, Asia and the Middle East.
Studying cannabis use and effects in other cultures and regions could help us understand the risk factors for cannabis psychosis much better. For instance, is the low incidence of psychosis in some regions of Asia linked to the smaller population of cannabis users there?
Again, is tobacco synergistic with cannabis in increasing the psychosis risk? Knowing this could enable us to focus on helping cannabis users quit tobacco to reduce this risk.
The study concludes that we need much more research to elucidate the risk factors for cannabis psychosis. This should include many more women cannabis users as well as other geographical areas of the world.
Hamilton says, “We need to accept that cannabis psychosis is about more than genetics or biology but is effected by social factors such as where and how young people grow up and the problems they experience as they develop.” The increasing legal access to cannabis in America “presents a large naturalistic experiment”, he says, which will provide data in a few years on how cannabis affects health and psychosis trends in the population.
Hamilton, I. and Monaghan, M. (2019). Cannabis and Psychosis: Are We any Closer to Understanding the Relationship? Current Psychiatry Reports. https://link.springer.com/article/10.1007%2Fs11920-019-1044-x