Findings from a large study into cannabis use shows that people who first use the drug to self-medicate for conditions such as anxiety, depression and pain face a higher risk of paranoia compared to people who start using the drug for fun or recreational reasons.
The research analysed responses from over 3,000 current or past adult cannabis users, who had no clinical history of psychosis and were part of the Cannabis & Me survey run by King’s College London (KCL) and the University of Bath. The researchers found that the reasons why a person chooses to use cannabis can increase their risk of developing mental health problems.
In addition, people who had experienced childhood trauma are more vulnerable to paranoia, and cannabis use was found to further amplify this risk depending on the type of trauma suffered.
The findings, published across two studies, identify key risk factors for severe paranoia among cannabis users. The first, in BMJ Mental Health, highlights the link between motivations for cannabis use and paranoia. In contrast, the second, in Psychological Medicine, explores how childhood trauma interacts with cannabis use to exacerbate paranoia.
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The survey was conducted over a two-year period, from March 2022 to July 2024, and included 3,389 participants, 76 per cent of whom were current users. Participants reported on their reasons for first using cannabis, their weekly THC consumption (the principal psychoactive component of cannabis), and their mental health status.
On average, users consumed 206 THC units per week, equivalent to between ten and 17 ‘joints’ per week, although this varied widely between users. Participants who started using cannabis for anxiety, depression, or because family members used it, consumed more THC per week. This equated to an average of 248, 254.7, and 286.9 THC units per week, respectively.
Researchers found that the reasons people start using cannabis are linked to paranoia and mental health outcomes. Those who started using cannabis to relieve pain or to ease anxiety, depression or minor psychotic symptoms were found to have higher paranoia scores, as well as higher levels of anxiety and depression.
In contrast, participants who started using cannabis for fun were found to have lower paranoia and anxiety scores, while using cannabis out of boredom was associated with slightly higher depression scores.
Dr Edoardo Spinazzola, a research assistant at KCL and the study’s first author, said: ‘Our study provides vital evidence on how the reason someone first starts using cannabis can dramatically impact their long-term health.’
He added: ‘This research suggests that using cannabis as a means to self-medicate physical or mental discomfort can have a negative impact on the levels of paranoia, anxiety, and depression. Most of these subgroups had average scores of depression and anxiety which were above the threshold for referral to counselling.’
Professor Tom Freeman, director of the Addiction and Mental Health Group at the University of Bath and one of the study’s authors, suggested that THC unit tracking could help people who are vulnerable to higher levels of cannabis use overall.
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‘In future, standard THC units could be used in a similar way to alcohol units – for example, to help people to track their cannabis consumption and better manage its effects on their health,’ he said.
In the second study, the researchers found a strong link between childhood trauma and cannabis use.
Over half of the participants of the Cannabis & Me survey (52 per cent) reported some kind of childhood trauma. Those who had experienced childhood trauma reported higher levels of paranoia.
The analysis showed that participants who had experienced sexual abuse reported the highest weekly THC consumption, followed by those with emotional and physical abuse histories. Cannabis use was shown to amplify paranoia, particularly for those who had experienced emotional abuse or household discord. Other types of trauma, such as bullying, physical abuse, sexual abuse, or neglect, did not show the same effect.
Dr Giulia Trotta, a consultant psychiatrist and researcher at KCL and the study’s first author, said: ‘We have not only established a clear association between trauma and future paranoia, but also that cannabis use can further exacerbate the effects of this, depending on what form the trauma takes.’
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The researchers say that the findings have clear implications for clinical practice, highlighting the importance of early screening for trauma exposure in individuals presenting with paranoia.