Pain is common among cancer patients, but many do not get adequate pain relief, the researchers noted.
The new study looked at more than 800 adults with cancer who took part in the US National Health and Nutrition Examination Survey between 2005 and 2014. The patients were compared with about 1 650 adults without cancer.
The findings showed that 40% of the cancer patients had used marijuana within the past year, compared with 38% of those without cancer.
People with cancer were also more likely to use prescription opioids than those without the disease – nearly 14% versus just over 6%, respectively.
When analysing rates of marijuana and opioid use among more than 19 000 survey respondents, including those with and without cancer, the investigators found increasing rates of marijuana use over the 10-year study period, probably because legislative changes increased its availability.
Drop in hospitalisations
More clinical trials are needed to asses just how effective medical marijuana is against cancer-related pain, said co-lead author Dr Kathryn Ries Tringale, of the University of California, San Diego.
Prescription opioid use remained stable among cancer patients, the study authors said.
A cancer diagnosis did not significantly affect the odds of substance abuse between 2005 and 2014, according to the study published online in the journal Cancer.
Study co-author Dr Jona Hattangadi-Gluth, noted that legalisation of medical marijuana has been associated with a drop in hospitalisations for opioid abuse or dependence. If patients are substituting marijuana for opioids, it may be an opportunity for reducing opioid-related illness and death, she suggested.
"Of course, it will also be important to identify risks and adverse effects of marijuana, which has not previously been studied on large randomized clinical trials, given its scheduling as a class 1 controlled substance," Hattangadi-Gluth said in a journal news release.
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