Cannabis amplifies postoperative pain

The use of cannabis appears to be associated with worse pain scores during the first 24 hours after surgery, reports a recent study presented at the recent Anesthesiology Annual Meeting 2022.

“Cannabis is the most commonly used illicit drug in the United States and increasingly used as an alternative treatment for chronic pain, but there is limited data that shows how it affects patient outcomes after surgery,” said Elyad Ekrami, MD, lead author and clinical research fellow of the Outcomes Research Department at Cleveland Clinic’s Anaesthesiology Institute.

“Our study shows that adults who use cannabis are having more—not less—postoperative pain,” he added.

Ekrami and his team conducted a retrospective cohort analysis of 34,521 adults who had undergone elective surgeries that lasted more than 1 hour and stayed in the hospital for at least 24 hours after the operation. During the first day following the procedure, cannabis users had a median of 45.0 in intravenous (IV) morphine equivalents of opioid consumption. [Anaesthesiology 2022, abstract A2061]

In comparison, patients who weren’t using cannabis consumed only a median of 36 IV morphine equivalents.

In terms of outcomes, median time-weighted average pain scores during the first 24 hours were 5.5 among cannabis users and 4.1 among controls. Inverse probability of treatment weighting (IPTW)-adjusted linear regression confirmed that the use of cannabis was associated with worse pain (difference in means, 0.58, 95 percent confidence interval [CI], 0.48–0.68; p<0.001).

In contrast, and despite baseline differences in consumption, cannabis use showed no significant association with opioid use during the first 24 hours after surgery (ratio of geometric means, 1.07, 95 percent CI, 0.96–1.19; p=0.19).

“The association between cannabis use, pain scores, and opioid consumption has been reported before in smaller studies, but they’ve had conflicting results,” Ekrami said. “Our study has a much larger sample size and does not include patients with chronic pain diagnosis or those who received regional anaesthesia, which would have seriously conflicted our results.”

Moreover, the current analysis enrolled a well-balanced study population, with groups that were balanced according to confounders such as age, sex, use of cigarettes and other illicit drugs, and psychological disposition.

The cannabis conundrum

In the US, cannabis is the most common illicit drug, with nearly 50 million reported users in 2019, corresponding to some 20 percent of the population, the researchers explained. Use rates have only been increasing over time.

Despite such prevalence, the pharmacological and pathophysiological links between use of the substance and pain, particularly after surgeries, continue to be unclear. While there have been several studies investigating cannabis use after surgery, the body of literature has largely been limited by small sample sizes and variations in patient inclusion criteria.

The present study sought to fill these gaps by including a large sample size and ensuring that patient subgroups were well-matched through IPTW. The findings will be able to alert clinicians to the different postoperative care needs of their patients, particularly as regards substance use.

“Physicians should consider that patients using cannabis may have more pain and require slightly higher doses of opioids after surgery, emphasizing the need to continue exploring a multimodal approach to postsurgical pain control,” Ekrami said.