People who begin using cannabis to alleviate pain, anxiety, or depression face a significantly greater risk of developing paranoia compared to those who use it recreationally, according to the largest study of its kind.
Experts suggest that these users are also consuming higher levels of THC, the psychoactive component of cannabis.
Separate analysis further indicates a link between childhood trauma and elevated paranoia among cannabis users. Researchers propose this connection could explain why individuals with a history of trauma might be more susceptible to the effects of cannabis.
In England, medicinal cannabis is currently prescribed by the NHS only for select patients, including children with rare and severe forms of epilepsy, people with muscle spasms caused by multiple sclerosis, and adults suffering from vomiting and nausea due to chemotherapy.
However, private clinics offer cannabis for a broader range of conditions, including chronic pain and various mental health problems.
When it comes to recreational use, cannabis is a class B drug and is illegal to possess, grow, distribute or sell in the UK.
One study, led by experts at the Institute of Psychiatry, Psychology and Neuroscience (IoPPN) at King’s College London and published in BMJ Mental Health, explored the reasons why people start using cannabis and if this impacted upon subsequent use.
Researchers analysed answers from the Cannabis&Me survey, which included 3,389 current and former cannabis users over the age of 18 from the London area who had no history of clinical psychosis.
They found that those who said they started using cannabis to self-medicate an illness, including pain, anxiety or depression, or because they were experiencing minor psychotic symptoms, had higher paranoia scores.
Those with the lowest scores were people who reported starting using cannabis for fun, or because they were curious.
The survey also asked about the frequency and strength of the cannabis being used, with researchers tracking the average weekly consumption of THC.
They found the average person consumed 206 units of THC a week, which they suggest is between 10 and 17 joints a week.
However, those who started using cannabis to help with anxiety or depression, or if a family member also used it, reported consuming 248, 254.7 and 286.9 average THC units, respectively.
Marta Di Forti, a professor of drug use, genetics and psychosis at King’s IoPPN, and clinical lead at the South London and Maudsley NHS Foundation Trust’s cannabis clinic for patients with psychosis, said: “Cannabis used for self medication is associated with a greater average consumption of THC, increased anxiety, depression and paranoia, and the reason why people first use cannabis might become an effective, and certainly a very inexpensive and easy tool, to identify cannabis users who might require monitoring, support, or even referral to intervention.”
Prof Sir Robin Murray, a professor of psychiatric research at the IoPNN, said: “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.
“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.
“And 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.”
Separate analysis of the Cannabis&Me survey, published in the journal Psychological Medicine, explored the relationship between childhood trauma, cannabis use and paranoia.
Just over half (52 per cent) of those who responded to the survey reported some form of childhood trauma.
Those who said they experienced physical and emotional abuse had paranoia scores around 35-40 per cent higher.
Those who reported experiencing sexual abuse as a child consumed more THC on average, following by those who had experienced physical and emotional abuse.
Dr Giulia Trotta, a consultant psychiatrist and researcher at King’s IoPPN, said: “Childhood trauma doesn’t just increase paranoia, but it also predicts heavier cannabis consumption. And if trauma is the main driver of paranoia, cannabis makes it worse.”
Dr Trotta suggests the findings “highlight the importance of early screening for trauma exposure in individuals presenting with paranoia”.
She added: “Cannabis doesn’t just increase paranoia risk for everyone, it has a bigger effect for someone with a history of emotional abuse and household discord.
“And this explains why some people with trauma may be more vulnerable to the effect of cannabis and others may not be as affected by cannabis use.”
