Unpicking The Link Between Cannabis and Psychosis
The relationship between drug use and mental illness is far from straightforward. There’s been a lot of talk around cannabis causing psychosis. Let’s take a closer look to explore what we know.
A longitudinal research study with a large sample found that the risk of psychosis is 6x higher in cannabis users.
This would suggest the drug increases the risk of mental illness.
Let’s not forget this is correlational research — doesn’t equal causation!
Interestingly, an existing diagnosis of psychosis was a stronger predictor of cannabis use which suggests the mental illness precedes drug use.
So, cannabis may be used to self-medicate. Drug use can often be a consequence of psychiatric problems, rather than the other way around. Particularly when mental health treatment is difficult to access (or perceived to be), people may seek out maladaptive ways to alleviate unpleasant symptoms. This does not come as a surprise as there is a large comorbidity among drug use and mental health difficulties — they often go hand-in-hand.
Another thing discussed in the literature is something called transient psychotic experiences. Cannabis intoxication may bring this about. This means the short-term effects of the drug can be attributed to psychotic symptoms. Delusions and hallucinations are not unheard-of amongst cannabis users but not necessarily a sign of mental illness.
These symptoms also subside after intoxication, so should not be labelled as psychosis.
The reasons why we see a cannabis-psychosis relationship might be due to the individuals which are more likely to develop psychosis being the same ones that are more likely to use cannabis.
This means there may be potential personality traits predisposing cannabis use and the development of psychosis.
We see this in genetics too. Individuals who have a genetic predisposition for psychosis and use cannabis, appear to have worse psychosis outcomes.
We can see this as an additive effect in biological vulnerability.
Psychosis may also impact the brains reward system by reinforcing drug use, resulting in increased vulnerability to additive behaviours.
That is why if you have mental health problems, drug use should be avoided as it can make things worse.
Epidemiological data has given some interesting conclusions to go on.
What’s been shown is that during time periods where drugs of abuse have peaked, corresponding rates of psychosis have remained unchanged.
Additionally, there are significant cultural differences in the rates of substance abuse, yet psychosis rates remain pretty constant.
So, if the two were causally related, surely this data would be more in sync? But it isn’t.
All in all, what we see is a higher rate of cannabis use amongst populations with psychosis than the general population.
As you may have picked up on, it is inherently difficult to study drug use. Research is all observational — all that can be done is look at what people choose to do overtime.
This is extremely biased as we are all different, doing things for varying reasons. And this means that the people that choose to use cannabis will be different to those that choose not to.
There isn’t any other way of doing this research though, it would be extremely unethical to do a randomised controlled trial prescribing half the participants cannabis just to see what happens.
I hope this information gives you a better idea around this complex link. I urge you all to consider these findings critically and to take the relationships we see at face value. Drug use does not cause mental illness, this link is much more complicated.
