A wealth of recent studies has suggested that cannabis products are not only effective for alleviating the types of debilitating chronic pain experienced by tens of millons people worldwide, but that access to these plant-derived medicines may also reduce the amounts of opioid drugs people take. Given that opioid dependency – and death by overdose – has reached epidemic-level prevalence, many in the scientific community see marijuana as a possible lifeline out of the crisis. 

But a large new investigation published today in The Lancet contradicts past research by finding that people with persistent non-cancer-related pain who used cannabis had no improvement in pain scores or increase in opioid discontinuation compared with those who do not, over a four-year period. 

The authors, led Dr Gabrielle Campbell at the University of New South Wales’ National Drug and Alcohol Research Centre, recruited 1,514 adults from across Australia who were prescribed opioids (including fentanyl, morphine, oxycodone, buprenorphine, methadone, and hydromorphone) for more than six weeks to treat pain lasting longer than 3 months. Subjects were surveyed about a variety of lifestyle and psychological factors, pain scores, pain self-efficacy (which gauges people’s perceived ability to perform activities while in pain), and past and current cannabis use at the study onset, then once a year for four years (2012 to 2016). At each visit, the authors confirmed whether or not subjects were still taking an opioid. 

Surprisingly, their analysis revealed that people who were using cannabis at any level of frequency reported higher pain severity scores, worse pain self-efficacy, and worse pain interference (the degree to which pain is interfering with daily activities) than those not using cannabis at years two, three, and four. Greater generalized anxiety disorder scores were significantly higher in cannabis users at all study points. 

Even after adjusting for multiple factors such as age, baseline pain, and opioid dose strength, the authors found no association between cannabis use during the past year and reduced opioid use the following year. They note that a greater proportion of those who never reported using cannabis had discontinued opioids at the end of the four years compared with those who did (21 percent vs 9 percent), but this comparison must be taken with a grain of salt as it did not reach statistical significance. 

“To our knowledge, this is one of the longest, in-depth, prospective studies of a community cohort of people with chronic non-cancer pain, examining the effects of cannabis use on pain and prescribed opioid use,” the team wrote. 

Of course, this research cannot provide the definitive answer about the benefits – or lack thereof – associated with medical marijuana due to several key limitations. Firstly, as Dr Campbell’s team concedes themselves, it is possible that the individuals who sought out marijuana were more distressed by their pain and had higher rates of anxiety in the first place, though it is puzzling that these individuals did not appear to improve over time while using it. 

Secondly, the study was conducted prior to Australia’s legalization of medical marijuana, meaning that the subjects who were taking it had to turn to illicit sources and likely did not have access to products specially designed for pain treatment such as high-CBD tinctures and edibles. These people were thus unable to create a structured pain management plan with a medical provider, which could have led to significant differences in outcomes. 

This study is sure to incite a fierce debate among the proponents and opponents of medical cannabis, and given the dire need for pain-managing drugs that don’t cause dependency (it is now estimated that more than 115 people die from opioid overdose every day in the US alone), both scientists and activists will continue pushing for more research.