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Some proponents of medical marijuana have claimed that its use against pain might help curb the ongoing crisis of opioid abuse.
But a new study refutes that notion, finding that state laws legalising medical marijuana have had little impact on the issue.
Little or no change
"When comparing the overall effect of use after versus before medical marijuana laws were passed, we found small increases in nonmedical use of prescription opioids and slight decreases or no change in prescription opioid use disorder among non-medical users of prescription opioids – even for states that allowed dispensaries," said study first author Dr Luis Segura. He's a doctoral student in epidemiology at Columbia University Mailman School of Public Health, in New York City.
For the study, the researchers analysed data from the National Survey on Drug Use and Health from 2004 to 2014. They looked at potential connections between individual prescription opioid use and opioid addiction and living in a state where medical marijuana is legal. The survey included about 70 000 people, aged 12 and older.
The study was published online in JAMA Network Open.
Some – but not all – prior studies on this issue found that opioid prescribing, prescription opioid abuse and opioid overdoses fell after medical pot became legal.
"The hypothesis generated from these studies is that after medical marijuana law enactment, health care professionals would be more likely to prescribe medical marijuana instead of opioid medications, and this in turn would reduce the chance of individuals to misuse prescription opioids and develop consequences," explained study senior author Dr Silvia Martins, an associate professor of epidemiology.
'Moves' not enough
However, "we tested this relationship and found no evidence that the passage of medical marijuana laws – even in states with dispensaries –was associated with a decrease in individual opioid use of prescription opioids for nonmedical purposes," she added.
So, relying on moves such as the legalisation of medical marijuana to curb opioid use may simply not be enough, Martins said. Instead, outreach targeted specifically at opioid users, "such as prescription drug-monitoring programs and laws on prescribing practices – are needed," she believes.
The Columbia findings mirror those from a study published in the Proceedings of the National Academy of Sciences, which was led by Chelsea Shover, a postdoctoral researcher at Stanford University.
Her team compared opioid abuse cases in states that did or did not legalise medical marijuana and found no association between medical marijuana laws and opioid overdose death rates.
In fact, the overdose death rate actually increased between 1999 and 2017 in states that legalised medical pot, rising by about 23%, according to the Stanford study.
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