New research suggests that using cannabis as a form of self-medication may worsen mental health outcomes, increasing paranoia, anxiety, and depression, particularly among individuals with a history of childhood trauma.
The findings come from two large-scale studies led by the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s College London, in collaboration with the University of Bath. Drawing on data from Cannabis & Me, the largest survey of its kind, researchers identified key risk factors linked to cannabis use and its impact on mental health.
Why People Use Cannabis Matters
The first study, published in BMJ Mental Health, analyzed responses from 3,389 adults, both current and former cannabis users. Participants detailed their reasons for starting cannabis, consumption levels, and mental health status.
Results showed that those who began using cannabis to cope with physical pain, anxiety, depression, or early psychotic symptoms reported significantly higher paranoia levels. In contrast, individuals who tried cannabis out of curiosity, enjoyment, or social reasons had the lowest levels of paranoia and anxiety.
“Our study provides vital evidence on how the reason someone first starts using cannabis can dramatically impact their long-term health,” said Dr. Edoardo Spinazzola, research assistant at King’s IoPPN and first author of the study.
Measuring Cannabis Consumption
The researchers also examined weekly intake of Tetrahydrocannabinol (THC), cannabis’s main psychoactive compound. On average, respondents consumed 206 THC units per week — equivalent to about 10 to 17 joints with a 20% THC concentration.
Those who used cannabis to manage anxiety or depression reported significantly higher consumption, averaging between 248 and 255 THC units weekly.
“A key finding is that individuals who first used cannabis to manage anxiety, depression, or due to family influence showed higher levels of use overall,” said Professor Tom Freeman of the University of Bath. He suggested that standardized THC units, similar to alcohol measures, could help track and manage consumption.
Trauma and Cannabis-Linked Paranoia
A second study, published in Psychological Medicine, examined the interplay between childhood trauma and cannabis use. More than half of participants reported experiencing trauma, with physical and emotional abuse most strongly linked to paranoia.
Those who endured sexual, emotional, or physical abuse also consumed higher levels of THC on average. Researchers found that cannabis use intensified the association between trauma and paranoia, with effects differing by trauma type.
“This is the first study to explore how trauma, cannabis use, and paranoia interact in the general population,” said Dr. Giulia Trotta, consultant psychiatrist and study lead. “Our findings underscore the importance of early screening for trauma in individuals presenting with paranoia.”
Clinical and Policy Implications
Professor Marta Di Forti, senior author of both studies, emphasized the broader significance for public health and policy.
“There are groups of people who start to use cannabis to cope with physical and emotional pain,” she said. “Our research confirms that this carries significant risks. Policymakers must carefully consider the health consequences of legalization, ensuring public education and clinical support are in place.”
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