Cannabis use in your 20s and 30s linked to earlier onset of psychosis, study finds

People who use cannabis in their 20s and 30s are developing psychosis years earlier than non-users, according to our new study, published today in the journal Biological Psychiatry.

This challenges the idea that delaying cannabis use until your mid-20s – when people believe their brain has finished developing – is a safer option to avoid the risks of psychosis.

Our research found that for people who were susceptible to psychosis, cannabis use in their 30s was associated with an earlier onset of psychosis by 6.3 years.

Cannabis use is becoming increasingly common. More than 2.5 million Australians use prescribed or illicit cannabis each year. It’s also increasing in potency.

But for many users, the psychiatric harms of cannabis are likely to outweigh any medical benefit. In fact, there is little evidence it’s effective for anxiety, depression or insomnia.

Psychosis is a spectrum of disorders, characterised by reality distortion. At the core of psychosis is the more severe and chronic form, schizophrenia.

A person with psychosis may experience confusion, mood swings and hallucinations – seeing or hearing something or someone who isn’t there. They may have false beliefs and might not make sense to others while speaking.

Psychosis affects around 0.5% of Australians of Australians. There is a strong genetic component to schizophrenia and psychosis. Environmental factors, including cannabis use, also play a role.

The most active ingredient of cannabis is delta-9-tetrahydrocannabinol, or THC. Both prescribed and illicit cannabis usually contain THC, often in high doses. However, prescribed cannabis is also available without THC.

THC works by locking onto the cannabis receptors, which are part of the brain’s endocannabinoid system.

When naturally functioning, the endocannabinoid system helps maintain physiological balance by regulating processes including appetite, immunity, memory, mood, pain, sleep and stress responses.

The cannabis plant evolved to exploit this system by producing the mind-altering compound THC, which acts as a skeleton key for the cannabinoid receptors.

Past research has found people who frequently use cannabis are more likely to experience psychosis and greater harms from psychosis.

In 2011, our research group showed cannabis use was associated with an earlier age of onset of psychosis.