People who use cannabis within a month before surgery experience greater pain after the operation than those who didn鈥檛.
have used marijuana, and 37 US states have now legalised medical marijuana. Given its widespread use, and the fact that cannabis with high amounts of the psychoactive compound THC has been shown to provide some pain relief, researchers wanted to understand how it could affect the experience of pain after surgery.
at Cleveland Clinic in Ohio and his colleagues looked at data on 34,505 adults who underwent surgery at the centre between January 2010 and December 2020. All surgeries lasted more than an hour and required participants to stay in the hospital for at least one day after. Of the participants included in the study, none of whom had chronic pain, 1683 reported using cannabis within 30 days before surgery, while the rest did not.
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Everyone rated their pain 24 hours after surgery on a scale of 0 to 10, with 0 indicating no pain and 10 indicating the worst pain possible. On average, people who reported using cannabis in the month prior to their surgery rated their pain a 5.5 compared with a pain score of 4.1 for those who didn鈥檛 report using cannabis in that time period. After adjusting for factors including age, surgery type, psychiatric history and other substance use, researchers found average pain scores still differed by 0.58 points between the two groups.
Average opioid use to relieve post-surgical pain was also 7 per cent higher in people who used cannabis compared with those who did not. While this difference was not statistically significant, it warrants future investigation, says Ekrami, who presented the findings 23 October at the American Society of Anesthesiologists鈥檚 annual meeting in New Orleans, Louisiana. 鈥淎ll clinicians want to limit opioid use in patients because it comes with [the risk of] side effects like respiratory complications and addiction,鈥� he says.
At first glance, these findings seem to contradict previous research showing that cannabis can reduce pain. There are two potential explanations for this, says Ekrami. The first is that some people who use cannabis do so to alleviate pain. Therefore, their pain increases when they can鈥檛 access the drug in the hospital.
Another idea is that because cannabis modulates pain by binding to certain cannabinoid and opioid receptors in the body, consistent use may desensitise these receptors, so opioids are less effective at reducing pain, says Ekrami.
A key limitation of this study is that people could have misreported their cannabis use over fears of being judged or having their procedure cancelled, says at NYU Langone Health in New York City.
鈥淚 think [this study] is important, but I think what鈥檚 even more important is the research that鈥檚 going to come out on post-operative pain relief when using these substances [in a clinical setting],鈥� he says.
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