OBJECTIVES: Over the past decade, opioid dispensing declined rapidly among U.S. patients with active cancer. Meanwhile, cannabis use increased substantially, driven partly by state medical cannabis legalization (MCL). This study aims to assess the associations between recent MCL and opioid- and pain- related outcomes for adult patients receiving active cancer treatment.

METHODS: This observational study used U.S. national commercial claims data and a difference-in-differences design to estimate the associations of interest for patients 18-64 who received anticancer treatment during the 6 months following a new (female) breast, colorectal, or lung cancer diagnosis. Main outcomes included ≥1 day of opioids, ≥1 day of long-acting opioids, morphine milligram equivalents if any opioid, and ≥1 pain-related emergency department visit or hospitalization (“hospital event”). Main analysis focused on patients residing in 34 states without MCL by 01/01/2012. Secondary analysis differentiated between MCL with and without allowances for legal dispensaries. All analyses allowed the associations to differ by patients’ recent history of prescription opioids.

RESULTS: MCL was associated with a reduction in the rate of ≥1 opioid day from 90.1% to 84.4% (a 6.3% relative percent difference [RPD], p=0.001) among breast cancer patients with recent opioids, from 89.4% to 84.4% (5.6% RPD, p=0.030) among colorectal cancer patients with recent opioids, and from 33.8% to 27.2% (19.5% RPD, p=0.016) among lung cancer patients without recent opioids. MCL was associated with a reduction in the rate of pain-related hospital events from 19.3% to 13.0% (32.6% RPF, p=0.028) among lung cancer patients with recent opioids. MCL with dispensary allowances were associated with larger reductions.

CONCLUSIONS: MCL implemented during 2012-2017 was associated with a lower rate of opioid prescriptions and pain-related hospital events among some adults receiving treatment for newly diagnosed cancer. The nature of these associations and their impact on patient safety and quality of life require further investigation.