April 19 (UPI) -- People who use medical marijuana have higher rates of medical and non-medical prescription drug use -- including pain relievers -- than others, according to a new study.
Researchers at Stanford University and University College Cork in Ireland analyzed more than 57,000 responses to the 2015 National Survey on Drug Use and Health to determine if medical marijuana users also turn to opioids. Their findings were published this week in the American Society of Addiction Medicine's Journal of Addiction Medicine.
In the survey, participants were asked about medical and non-medical use of prescription drugs. About 1.4 percent of all respondents, 776 people, said they used medical marijuana.
Survey participants who use medical marijuana were 60 percent more likely to report prescription drug use, for medical reasons or not, than those who did not use medical marijuana, researchers report.
Medical marijuana users were also more than twice as likely to report non-medical use of prescription drugs, including pain relievers, stimulants and tranquilizers.
"Non-medical use of pain relievers is of particular interest because of pain relievers' role in the opioid overdose epidemic," the researchers wrote.
Previous studies have shown that states where medical marijuana is legal have lower rates of medical and non-medical prescription drug use and related harms -- including opioid overdose. Thirty states and the District of Columbia have laws legalizing some form of marijuana use, including eight states that have legalized it for recreational use.
"These reports have led many to believe that use of medical marijuana is a protective factor against non-medical prescription drug use," Theodore L. Caputi, a researcher at University College, said in a press release. "However, individual-level inferences cannot be made using the ecological studies cited frequently in the debate over medical marijuana."
Caputi said previous data has shown the relationship between medical marijuana use and use of non-medical prescription drugs, and should be used as a marker for high risk patients -- but adds that additional research is needed on whether cannabis is being used together with or in place of prescription drugs.
Dr. Marcus A. Bachhuber and colleagues at Montefiore Medical Center/Albert Einstein College of Medicine in New York wrote in an accompanying article in the journal that the study doesn't show that medical cannabis causes increased use of prescription drugs.
"Given that people who take medical cannabis and those who do not are likely to have different underlying morbidity, it is possible that medical cannabis use reduces prescription drug use yet prescription drug use remains relatively high in that group," they wrote in the article.
They noted that chronic pain is the most common reason for medical marijuana use, and people in other studies who use medical marijuana consistently report substituting cannabis for other drugs.
In 2017, the National Academies of Sciences, Engineering and Medicine issued a report concluding that pot can significantly reduce pain symptoms.
"To fully understand the effect of medical cannabis on the use of other drugs, prospective longitudinal studies randomizing patients to cannabis versus other treatments are urgently needed," they wrote.