"The things psychologists would be most worried about were worse, but the thing patients were using the cannabis to hopefully help with — namely pain — was no different,” Rogers told MedPageToday. "Co-use of substances generally leads to worse outcomes. As you pour on more substances to regulate anxiety and depression, symptoms can go up."



A large Australian study in The Lancet Public Health found that cannabis use was common in patients with chronic non-cancer pain who were prescribed opioids, but “there was no evidence that cannabis use reduced pain severity or interference or exerted an opioid-sparing effect.”



This research, known as the Australia POINT study, followed over 1,500 chronic pain patients for almost four years. Although its methodology has limitations, it is one of the largest long-term studies of opioids and cannabis under real-world conditions.

“At each assessment, participants who were using cannabis reported greater pain and anxiety, were coping less well with their pain, and reported that pain was interfering more in their life, compared to those not using cannabis,” said lead author Gabrielle Campbell, PhD, of the University of New South Wales.



In other words, the opioid-sparing effect of cannabis seems not to work well in the real world, despite its apparent success under laboratory conditions. There are several possible factors at work.



First, laboratory conditions are artificial. Studies often use lab animals or healthy human volunteers. But people with chronic health conditions may be different. Or perhaps people who are experienced with cannabis and willing to spend a day in a laboratory being subjected to painful stimuli are different.



Second, laboratory studies are often short term, but chronic pain is long term. The cumulative risks of opioids and cannabis, as well as the complex interactions between them, may take time to unfold and discover. It is possible that an initial opioid-sparing benefit washes away quickly and is replaced by nontrivial risks.



Third, real-world studies emphasize patient outcomes, a factor that laboratory work cannot assess. Because outcomes are so important, studies that focus on them must be given greater weight.



More research will be needed to sort out the effects of combining cannabis and opioids in chronic pain management. But at present, clinical studies point to more risks and harms than benefits. Perhaps a subset of patients or a particular combination of a specific opioid and cannabis preparation will change this. Or perhaps combining cannabis and opioids is not such a great idea.