People who use cannabis to alleviate pain, anxiety or depression are more likely to develop paranoia than recreational users, according to a new study published in BMJ Mental Health. The research, led by academics at King's College London, analysed responses 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.
The study found that those who started using cannabis to self-medicate for conditions such as pain, anxiety or depression, and who also experienced minor psychotic symptoms, had higher paranoia scores. In contrast, users who consumed cannabis for fun or curiosity reported the lowest paranoia levels. The average respondent consumed 206 units of tetrahydrocannabinol (THC) per week – equivalent to 10 to 17 joints – but those using cannabis for anxiety or depression consumed 248 and 254.7 units respectively.
Professor Robin Murray of King's College London cautioned against the widespread belief that cannabis is medicinal. 'Contrary to what it says on the internet, cannabis is not medicinal,' he said. '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, chair of the Royal College of Psychiatrists' addiction faculty, emphasised the public health implications. 'These important findings reinforce previous work which suggests that cannabis can have significant adverse effects on users' mental health,' she said. '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.'
A separate study in Psychological Medicine, analysing the same survey, found that 52% of cannabis users had experienced childhood trauma, and those who suffered physical or emotional abuse had paranoia scores 35–40% higher. Respondents who reported sexual abuse as a child consumed the most THC on average.
