Chronic pain is estimated to affect around 20% of people worldwide – a figure that is mirrored in the US where, in 2019, 21% of Americans experienced chronic non-cancer pain, defined as pain from conditions that occur on at least half of days for three or months. While the use of conventional treatments such as painkillers (including opioids) remains prevalent, a growing number of patients are turning to medical cannabis as states continue to legalise access to cannabis-based products for medicinal purposes.
Medical Cannabis and Chronic Non-Cancer Pain
Today, chronic pain is the most reported reason for medical cannabis use globally. At the time of writing, a total of 38 states and the District of Columbia (D.C.) have legalised the medicinal use of cannabis. Advocates for access to medical cannabis and the cannabis industry itself have suggested that medical cannabis may offer at least a partial solution to the ongoing opioid crisis which was associated with over 80,000 overdose deaths in the US alone in 2021. However, evidence for the effectiveness of medical cannabis in the treatment of chronic non-cancer pain remains limited with mixed results.
Past studies have suggested an association between medical cannabis legalisation and reduced prescription opioid use. However, there are limitations to this research, as it is limited by general population and repeated cross-sectional samples in which most people do not have chronic noncancer pain and changes in pain treatment within persons over time are not observed.
Furthermore, other findings – including that people who use medical cannabis are more likely to misuse prescription opioids – paint a conflicting picture. Therefore, the authors of a recent study aimed to “examine how state medical cannabis laws influence the receipt of guideline-concordant non-opioid, non-cannabis pain treatments among patients with chronic non-cancer pain”.
Design and Methods of the Study
The researchers identified 12 states that have implemented medical cannabis laws but had not legalised recreational cannabis between 2014 and 2019 (Arkansas, Connecticut, Florida, Louisiana, Maryland, Minnesota, North Dakota, New Hampshire, New York, Oklahoma, Ohio, and Pennsylvania). Each state had four years of pre-law data and three years of post-law data. Data from 17 comparison states in which medical cannabis had not been legalised were used to construct 12 comparison groups aligned with each medical cannabis state’s specific 7-year study period.
Data from deidentified insurance claims from September 2010 to July 2022 were used to create a sample of adults aged years 18 or older who were continuously enrolled in commercial or Medicare Advantage insurance for each state’s 7-year study period and were diagnosed with conditions associated with chronic non-cancer pain (e.g., arthritis, low back pain, serious headache, fibromyalgia, neuropathic pain). Patients were included if they had one in-patient or two out-patient diagnosis codes for a given qualifying condition in the four years before medical cannabis law implementation.
Measures used to determine the effect of medical cannabis law on treatment for chronic non-cancer pain included: the proportion of patients receiving any opioid prescription, nonopioid prescription pain medication, or procedure for chronic noncancer pain; volume of each treatment type; and mean days’ supply and mean morphine milligram equivalents per day of prescribed opioids, per patient in a given month. Augmented synthetic control analyses were used to estimate effects on receipt of chronic non-cancer pain treatment, relative to predicted treatment receipt in the absence of these laws.
Results of the Study
In a given month in the four years before law implementation in medical cannabis states and their synthetic controls, an average of 5.47% of patients received any opioid prescription, 9.12% received any non-opioid prescription pain medication, and 8.50% received any pain procedure.
In a given month in the three years post-law implementation, medical cannabis law states had an average decrease of 1.07 percentage points in the proportion of patients receiving any opioid prescription, relative to a decrease of 1.12 percentage points in the synthetic control group; an average increase of 1.14 percentage points in the proportion of patients receiving any nonopioid prescription pain medication, relative to a 1.19 percentage point increase in the synthetic control group; and a 0.17 percentage point decrease in the proportion of patients receiving any pain procedure, relative to a 0.001 percentage point decrease in the synthetic control group.
These findings rule out an important effect of medical cannabis laws on the chronic non-cancer pain treatment outcomes measured in this study. Medical cannabis legal implementation had an average estimated effect of less than 0.2 percentage points on the proportion of patients receiving an opioid prescription, non-opioid painkiller prescription, or a pain procedure. Furthermore, among patients who were prescribed opioids, the average estimated effects of medical cannabis laws on days’ supply and dose were consistently small in magnitude.
The researchers note the results of a recent survey of a representative sample of adults with chronic non-cancer pain in states with medical cannabis laws, of which 31% reported using medical cannabis to manage their pain and over half perceived that their use of cannabis led them to decrease their use of prescription opioid and non-opioid medications. However, the results of the current study suggest that “such substitution has not led to large shifts in pain treatment patterns at the population level.”
The authors conclude that this study “did not identify important effects of medical cannabis laws on receipt of opioid and nonopioid treatment among patients with chronic non-cancer pain.” Nonetheless, given the associated risk and side effect profile of opioid medications, future research should continue to gather evidence to identify novel therapies which may help to reduce the reliance on opioid medications in this setting.
