A recreational drug’s relaxing reputation might be more complicated. Recent research has found a link between cannabis use and increased violent behavior.
Scientists in the UK examined the literature on cannabis and violence. People who regularly used cannabis were significantly more likely to commit a violent act than non-users, they found; they were also more likely to be a victim of a violent act. Though the research doesn’t prove a cause-and-effect link, it suggests that cannabis use might be an important and potentially modifiable risk factor for interpersonal violence, the authors say.
“The findings of our study underscore the importance of addressing this issue at both a societal and clinical level,” they wrote in their paper, published late last month in the journal Psychological Medicine.
Cannabis and violence
Enjoyable as cannabis is for many people, it isn’t without its potential harms, especially in larger doses over a long period of time. Some studies have pointed to an increased risk of violence linked to cannabis among certain groups, such as younger children and people with existing severe mental illness. According to the authors, however, it’s been unclear whether this risk can be seen in the average cannabis user, too.
The researchers conducted a large review of 63 cannabis-related studies that collectively involved a quarter-million people. These studies looked at people in the general population as well as patients receiving psychiatric care.
Overall, the researchers found, cannabis use was associated with a twofold higher risk of perpetrating violence among the general population. The risk of violence was roughly 2.5 times higher among psychiatric patients who used cannabis. This added risk was even more noticeable when the researchers only looked at violence that led to a criminal conviction (3.75 times higher in the general population). Interestingly enough, people who used cannabis were also around 50% more likely to be the victim of violence.
“As a clinician, I’ve seen how heavy cannabis use can be a factor in violence. We’ve been cautious for a long time about how far we could go in describing this link, but a review of this size lets us speak with more confidence about the risks, while being careful not to stigmatize people who use cannabis more broadly,” said study author Marta Di Forti, a professor of drug use, genetics and psychosis at Kings College London, in a statement from the university.
What should this mean?
Di Forti and her co-authors note this review can only demonstrate a correlation between cannabis and violence, not a definitive causative effect. And because they looked at different types of studies and populations, the strength of this association might not be set in stone. Studies that followed people over time found a smaller, but still significant, added risk of violence associated with cannabis than studies that only looked at people at a single point in time, for instance.
That said, there are plausible reasons as to why cannabis, particularly heavy cannabis use, could increase people’s tendency for violent behavior, the researchers say. Cannabis can impair people’s attention, executive function, inhibition, and problem-solving abilities, and prolonged heavy use can negatively affect people’s ability to regulate their emotions, including anger. People who regularly use cannabis are also more prone to feelings of paranoia.
Some of this added risk may represent other indirect factors, the researchers say. People who regularly use cannabis tend to be more impulsive in general and engage in other risk-taking behaviors more than those who don’t use it, according to the authors. Similarly, cannabis users might be victims of violence more often due to being in riskier situations on average, rather than a direct causative effect of the drug itself.
The researchers argue that the “association between cannabis use and violence is likely to reflect multiple interacting pathways rather than a single direct causal mechanism.”
Importantly, many of these studies were conducted before the advent of today’s cannabis products that contain much higher levels of THC. Other research has suggested that high THC cannabis is more dangerous in several ways than the products of the past, so these findings might be an underestimate if anything.
Of course, many people use cannabis without ever hurting others or themselves. And the potential harms of cannabis, as with other recreational drugs like alcohol, seem to be most pronounced among chronic heavy users, not the occasional toker. Still, though cannabis alone might not turn someone into the Hulk, the researchers say that it should be seen as a meaningful risk factor for violence—one that ought to be addressed when needed.
“From a public health perspective, violence should be considered alongside other established cannabis-related harms when developing prevention strategies, public education campaigns, and regulatory policies, particularly in jurisdictions where cannabis has been legalized or decriminalized,” they wrote.
