Study links self-medicating cannabis use to higher risk of paranoia

A large-scale survey has suggested that the reasons people begin using cannabis may determine their likelihood of developing mental health problems, and it has found that those who turn to the drug for relief from pain, anxiety or depression are more prone to paranoia than recreational users.

The research, published in the British Medical Journal and led by King’s College London, assessed responses from 3,389 adults who had used cannabis but had no clinical history of psychosis, and it revealed that patterns of motivation and consumption strongly influence psychological outcomes.

Participants who reported using cannabis to self-medicate and who also showed minor psychotic symptoms recorded notably higher paranoia scores, whereas those who used cannabis mainly out of curiosity or for enjoyment had the lowest scores, and the findings indicate that cannabis has a graded effect similar to alcohol or food, with risks increasing in line with heavier consumption.

The survey estimated that the average user consumed about 206 weekly units of tetrahydrocannabinol (THC), which corresponds to between 10 and 17 joints, but individuals who used cannabis specifically to manage anxiety or depression consumed much higher levels, averaging 248 and 254.7 units respectively, and this raised concerns that vulnerable groups may be at greater risk through heavier intake.

Although medicinal cannabis prescriptions on the NHS are confined to limited conditions such as rare epilepsy, chemotherapy-related nausea and certain forms of multiple sclerosis, the study highlighted that private clinics across the UK now widely market cannabis as a treatment for pain, anxiety and depression, and critics argue that such practices risk fuelling the very problems the drug is claimed to alleviate.

The Royal College of Psychiatrists’ addiction faculty has warned that cannabis is the most commonly used illicit substance in the UK and that around one third of users develop a problematic relationship with it at some point, a proportion comparable to alcohol dependence, and long-term use of natural or synthetic cannabinoids carries risks of addiction, low motivation, depression and anxiety.

Daily use of high-potency cannabis has been associated with a fivefold increase in the likelihood of developing psychotic disorders, with adolescents identified as a particularly vulnerable group, and experts stress that substance use and mental health services require greater resources to manage these risks.