Does Cannabis Cause Psychosis?

The definition of psychosis is a break with reality that shows up in the form of delusions, hallucinations and disordered thinking. Psychotic episodes can last for days, months or even years. Even a brief psychotic episode can mark the beginning of lifelong psychiatric disorders such as bipolar or schizophrenia.

From decades of clinical work, there have been numerous cases of psychosis that have first come to light in the context of cannabis use. On one hand, this isn’t startling, as it's more conceivable that people will start using cannabis at the same age that they can be at the greatest risk of a first episode of psychosis, that being their teens or 20s. However, there is evidence of too many cases where the timing was just too close to ignore as just a coincidence.

It may be easy to claim that cannabis causes psychosis or schizophrenia, especially for those who want to stigmatize cannabis use. However, there are several other plausible connections.

For example, those who are at risk for psychosis may self-medicate with cannabis before developing the disorder. In this case, before the outset of psychosis, the patient may experience anxiety and use cannabis to feel better. Whilst cannabis may not help, it often doesn’t cause psychosis. In contrast, symptoms of emerging psychosis might lead people to self-medicate with cannabis. This means that, in some cases, the psychosis may be the driving force of cannabis use, not the other way around.

Secondly, cannabis may have the effect of triggering or worsening psychosis without being a direct cause. Other drugs, including psychostimulants, steroids, alcohol and psychedelics can initiate a momentary substance-induced psychosis, which may last anywhere from days to months. However, of all the drugs linked with this uncommon form of psychosis, cannabis is the most common culprit.

Amongst those living with substance-induced psychosis, cannabis users have been found as the most likely to eventually develop schizophrenia. This would indicate that cannabis is not just causing transient psychosis, but also schizophrenia. 

Simultaneously, studies have shown that these patients have a more elevated genetic risk for schizophrenia. This means that cannabis may just trigger what the patient is predisposed to suffer from in the long term.

To complicate things even more, there is a third reason behind the association between cannabis and psychosis. There is evidence that specific genes may mean that a person is predisposed to both cannabis use and psychosis.

Should you be worried about using Cannabis?

It is unlikely that cannabis use alone causes schizophrenia. Rates of schizophrenia have not risen in the last 70 years, while the rates of  cannabis use across the globe have gone up from hundreds of thousands in the 1950s to hundreds of millions today. If cannabis did cause schizophrenia then the rates of schizophrenia would have risen alongside the huge increase in cannabis use, and they have not.

Still, if cannabis can bring forward the onset of schizophrenia in vulnerable people, then that by itself is a massive public health issue. Earlier onset of schizophrenia means that people have less biological and psychological growth before the schizophrenia adversely influences their brain development and adult coping skills. That could lead to worse outcomes and more symptoms of schizophrenia such as paranoia and delusions.

With all this in mind, it is wise for those with a family history of schizophrenia or other psychotic disorders to be very cautious when it comes to cannabis. Even those with blood relatives suffering from other psychotic disorders or severe mental illnesses should exercise a lot of caution when it comes to cannabis. Additionally whilst we may not know whether potent forms of cannabis containing extremely high THC  levels are more likely to trigger psychosis, they might be.

Given the normalisation and acceptance of cannabis we are currently seeing worldwide, it is important to understand the actual benefits and risks that accompany the use of cannabis. Cannabis is used to relieve chronic pain, stress, nausea, insomnia and many other conditions.

It must be remembered that no medication is entirely safe for everyone and that all medications can have potential side effects.  We should encourage everyone, especially teens and young adults who carry the risk factors of psychosis to postpone their use of cannabis until they are passed the age when the initial onset of schizophrenia and other psychotic conditions is most conceivable. We should not subscribe to the idea that cannabis causes psychosis, but its good to understand the associated risks.

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