Cannabis does not cause psychosis.

Cannabis does not cause psychosis.

By Richard Shrubb

One of the hardest hitting arguments against cannabis is that it ‘causes psychosis’. It doesn’t – researchers have been looking for links for nearly 90 years and has found no link at all.

When you see some mad politician, high on power and money, ranting like a lunatic that ‘cannabis causes psychosis’, remember this article and suggest kindly he sees a psychiatrist about his megalomania and paranoid delusions. Let’s now go into a little depth.

Paranoid schizophrenic? Leave weed alone

I came into cannabis writing because I had spoken to experts and read research over many years and despite what my mental health teams had told me, I concluded that cannabis didn’t cause my paranoid schizophrenia.

However, the sensations and thoughts that enter my head increase significantly when I am under the influence of cannabis. Paranoid schizophrenia is different to classic schizophrenia in that we suffer extreme paranoia and don’t always hear voices. The diagnosis of schizophrenia is often given to people experiencing 20 or more different illnesses – often enough to people psychiatrists can’t / don’t want to help such as BME and LGBT minorities.

Those with acute mental illness should leave most recreational drugs alone – did you know that war criminal Tony Blair’s press secretary Alastair Campbell had alcohol psychosis? Floridly psychotic and Sectioned he was asking to see his then employer, Leader of the Opposition Neil Kinnock to get him out of there. You can imagine the response of the psychiatric team at the time until Kinnock popped by to see how he was.

On half a bottle of decent Czech absinthe during my Master’s Degree, I ended up chasing hallucinated rats around the house, scaring the shit out of my housemates. Mind-bending drugs are not for me thanks!

Decrease in schizophrenia / increase in cannabis use?

NORML UK: working to reform cannabis laws. In 2012 I looked at the links between cannabis use and schizophrenia for a blog for the cannabis legalisation organisation NORML UK. I found a quote from the Lancet medical journal: “A declining incidence of treated cases of schizophrenia over the period when cannabis use has increased suggests, however, that cannabis use is unlikely to have caused cases of schizophrenia that would not otherwise have occurred.

That would suggest that Canada and several states in the US that have legalised cannabis could well see a decrease in acute mental health cases as opposed to this widely propagated idea that cannabis psychosis rates would increase.

I have since searched for this quote but instead found a Guardian article from this week by two medical scientists that said, “It is also worth noting that 10-fold increases in marijuana use in the UK from the 1970s to the 2000s were not associated with an increase in rates of psychosis over this same period, further evidence that changes in cannabis use in the general population are unlikely to contribute to changes in psychosis.” This reinforces the lack of a link between cannabis use and psychosis

For the NORML UK article, I interviewed Harry Shapiro, Director of Communications at drugs support charity Drugs Scope who told me, “I have heard from schizophrenics that cannabis can actually dampen the voices they hear.” I have since spoken to an Arizona psychiatrist who suggests to her new schizophrenics to get a cannabis medical card for a bad back and to try high CBD weed to dull the voices in their heads – she has seen many people do very well on weed.

2019 – scientists speak out in the Guardian

Carl Hart and Charles Ksir published an opinion piece in the Guardian this week, railing against an opinion piece in the New York Times by a book author who was out to get cannabis.

They stated: “It is true that people diagnosed with psychosis are more likely to report current or prior use of marijuana than people without psychosis. The easy conclusion to draw from that is that marijuana use caused an increased risk of psychosis, and it is that easy answer that Berenson has seized upon. … In our many decades of college teaching, one of the most important things we have tried to impart to our students is the distinction between correlation (two things are statistically associated) and causation (one thing causes another). For example, the wearing of light clothing is more likely during the same months as higher sales of ice-cream, but we do not believe that either causes the other.”

Paranoia can make you confuse correlation with causation. The radio DJ may say something relevant to something I have just mumbled to myself in front of the radio but s/he isn’t listening to me (though at times for me this is difficult to unbelieve thanks to the bad wiring in my brain). In the same light as this, you could almost call the idea that cannabis causes psychosis delusional in its own right.

Richard Shrubb

Richard is a marijuana, water sports and electric vehicles writer based in Dorchester, Dorset. Living in Prince Charles model housing estate, Poundbury, he is an avowed republican, community and Labour Party activist. Visit his website at for more about what he does.

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