The fact that opioid use stayed flat is “congruent with results from other studies, which suggest that medical cannabis legalization is associated with lower opioid prescribing,” according to Kevin F. Boehnke, PhD, a research investigator in the department of anesthesiology and the Chronic Pain and Fatigue Research Center at the University of Michigan in Ann Arbor. “However, it could also be due to tightening opioid prescribing standards in the age of the opioid crisis.”

Similarly, the increase in marijuana use across the entire cohort likely reflects state legislative changes and increased access to cannabis.

Plus, the analysis didn’t specifically look at the use of cannabis in a controlled setting, where patients could be monitored by a physician or an oncologist, specifically. It included self-reports of all substance use (including illicit drugs other than marijuana, such as cocaine, heroin, and methamphetamines) in any setting. “It would have been nice to see whether medical cannabis use (rather than just cannabis use) affected odds of opioid use among individuals with cancer, but that’s a limitation of this dataset, as the authors mention,” noted Dr Boehnke. Plus, “there are likely differences in use patterns (eg, administration routes and cannabinoid preferences) between younger and older individuals using cannabis,” Dr Boehnke observed. “In any case, it is clear that more research is needed to better understand how to effectively use cannabis in the cancer context.”

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The current study included respondents aged 20 to 60 years, but according to the National Cancer Institute, the median age of a cancer diagnosis is 66 years — so, nearly half of all cancer cases may not have been captured in this sample as a result.2 The study’s age parameter specifically eliminates inclusion of the approximately one-quarter of new cancer cases that occur in the population of individuals aged 65 to 74 years.

It also does not include some of the most vulnerable populations, such as children and adolescents younger than 20 years who are diagnosed with cancer. Although individuals in this age subgroup have a low incidence of all cancers, they have higher risks of bone cancer and leukemias, specifically.


  1. Tringale KR, Huynh-Le M-P, Salans M, Marshall DC, Shi Y, Hattangadi-Gluth JA. The role of cancer in marijuana and prescription opioid use in the United States: a population-based analysis from 2005 to 2014 [published online April 22, 2019]. Cancer. doi:10.1002/cncr.32059
  2. National Academies of Sciences, Engineering, and Medicine. The Health effects of cannabis and cannabinoids: the current state of evidence and recommendations for research. Washington (DC): National Academies Press (US); January 2017.