Can Cannabis Cure Psychosis?

Despite recent research, the answer is still probably no

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Pictured: Green

Cannabis is a perennial topic of interest, partly because it may be useful as a treatment for a scant few medical conditions, but mostly because it is really fun getting high*.

So when a story is published saying that cannabis might be useful in treating psychosis, we leap on it with feverish abandon.

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“A new reason to get high? HURRAY!”

The same thing happens whenever a story is published saying that booze is good for you or that chocolate is healthy. We love a story that tells us that the thing that we’ve been avoiding is actually — shock! — good for us!

Sadly, much like the drinking and chocolate myths, this newest story is almost certainly untrue.

Cannabis probably can’t treat psychosis.

The study that I am talking about is a recent randomized-controlled trial comparing the effects of cannabidiol (CBD)— a chemical component of cannabis — on the brain chemisty of people who were at risk of psychosis and healthy controls. They used MRI scans to assess the differences in the brain that occurred after taking 600mg of CBD or an inert placebo. While the results are extremely complex to unpack, the essential finding was that the dose of CBD appeared to make the brains of the psychosis group slightly more like the brains of the control group than the placebo did.

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If that sounds confusing to you, remember that this is the simple version

Basically, CBD appeared to help normalize the brains of people at risk of psychosis.

Unfortunately, this is an almost meaningless finding to the individual.

Firstly, these were not people with psychosis. The authors specifically excluded people with “psychotic or manic episodes, neurological disorders, or a current DSM-IV diagnosis of substance dependence, IQ less than 70”. The participants in this research were people classified “at high clinical risk” of psychosis, and if that sounds like an opaque definition that’s because it really is. It is very hard to determine exactly what this means from the study, because they recruited people who a clinician had, at some point, enrolled in a mental health preventative program for psychosis.

Not ideal if you want to generalize to patients with diagnosed mental health issues.

The results were also incredibly hard to apply in a real-world setting. While “activation in the CBD group was intermediate to that in the placebo and control groups” might be a statistically significant finding, it’s pretty much meaningless in the real world unless you can put every single person with psychosis into an MRI and keep them there indefinitely.

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A small extract from the results. This is fascinating, but not that useful

The sample size was also far too small to generalize to the population: 33 people in the ‘psychosis’ condition and 19 controls. This is barely enough to detect a massive result, making it very unlikely that these results have much meaning at all.

The thing is, this study was not designed to test whether CBD was effective at improving psychosis. The idea that it was appears to have been entirely fabricated by some journalists desperate for an interesting story.

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*Cough* Daily Mail *Cough*

This study was actually aimed at identifying whether CBD could be of potential benefit; as with most MRI trials, it was small by design because MRIs are absurdly expensive, and the small sample size isn’t an issue in a pilot of this nature. The paper ends by suggesting that this effect should be trialed in a clinical setting, because obviously it should. 52 patients is not enough to conclude much of anything.

And, of course, anyone who read the study would know this.

To be fair, the study was incredibly dense. Reading it would be a chore even for a neuroscientist with a specialization in cannabis. But there were some shining examples of good science journalism on the issue. A piece in The Guardian managed to convey both the interesting nature of this research and the caveat that it’s basically useless as a guide for the individual at this point.

Sadly, there was far more nonsense than thoughtful reflection. There often is.

It’s also worth noting that while the research on CBD specifically is equivocal, there is a lot of evidence that cannabis use is associated with psychosis. There may be some benefit from CBD, but it’s going to take a while to figure out exactly what that is, especially considering the likely harms of other cannabinoids.

So what about this study?

Ultimately, it was some very interesting research. In a decade’s time, we might even see a treatment based on it.


This study did not demonstrate that CBD, or cannabis, is effective at treating psychosis. It didn’t even study people with psychosis. It was formative, early research on a tiny number of participants that has very little connection to actual people being treated for mental health issues.

Don’t believe the hype.

We still don’t know if CBD can treat psychosis.

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*Yes, I said it’s fun. We should legalize recreational cannabis, the harms of criminalizing it far outweigh the potential risks associated with legal cannabis.

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