Cannabis users who are self-medicating run higher risk of paranoia, study finds

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August 27, 2025

Those who take drug because of pain, anxiety or depression found to be more likely to develop paranoia than recreational smokers

People who start smoking cannabis to alleviate pain, anxiety or depression are at a higher risk of developing paranoia than those who use the drug recreationally, a study has found.

The research analysed answers from 3,389 former and current cannabis users aged over 18, who had no clinical history of psychosis and had taken part in the Cannabis&Me survey.

Published in BMJ Mental Health, and led by academics at King’s College London, the research found that those who started using cannabis to self-medicate for a condition such as pain, anxiety or depression, and if they were experiencing minor psychotic symptoms, had higher paranoia scores, while those with the lowest scores used cannabis for fun or because they were curious.

The survey also found that the average respondent consumed 206 units a week of tetrahydrocannabinol (THC), the active ingredient in cannabis, the equivalent of between 10 and 17 joints, but people who used cannabis for anxiety or depression reported consuming 248 and 254.7 units respectively.

Only people with very rare forms of epilepsy, adults with nausea caused by chemotherapy and some people with multiple sclerosis are able to get an NHS prescription for medicinal cannabis in England.

“I think lots of people who now know that cannabis can cause psychosis, they say ‘these people are not like me’. That’s not true,” said Robin Murray, a professor of psychiatric research at King’s College London.

“What we can show in this study is that the effect of cannabis is a bit like the effect of alcohol or the effect of food, that it’s a dimension. So the more you take, the more problems you get into.

“Contrary to what it says on the internet, cannabis is not medicinal. We now have 40 private clinics up and down the UK dishing out cannabis supposedly as a treatment, and the things that they are giving it for are pain, anxiety and depression predominantly. And these are the things that we find are related to people getting into trouble and becoming more paranoid.”

Dr Emily Finch, the chair of the Royal College of Psychiatrists’ addiction faculty, said: “These important findings reinforce previous work which suggests that cannabis can have significant adverse effects on users’ mental health. Society must be more aware of the substantial evidence on cannabis harms, and correct the widespread misapprehension that cannabis is not an addictive substance.

“Cannabis is the most widely used illicit substance in the UK, and around a third of people who use cannabis develop a problem with the drug at some point during their lives. This is similar to the proportion of people who will develop a problem with alcohol.

“The use of both natural and ‘synthetic’ cannabinoids over the long term risks addiction and severe co-occurring mental illness harms. Daily cannabis use is associated with depression, anxiety and reduced motivation.

“Daily users of high-potency cannabis are nearly five times more likely to develop a psychotic disorder than people who have never used cannabis, with adolescents at particular risk.

“As a priority, the UK government must provide substance use and mental health services with the training, staff and funding they need to support people with co-occurring substance use and mental illness. This must also include a focus on providing early treatment to the increasing number of children and young people struggling with substance misuse if we are to reduce long-term harms.”

A separate study published in the journal Psychological Medicine analysed the same survey, and found 52% of cannabis users had experienced some kind of childhood trauma, and that those who had experienced physical and emotional abuse had paranoia scores around 35-40% higher.

Respondents who reported experiencing sexual abuse as a child consumed more THC on average, followed by those who had experienced physical and emotional abuse.