The idea that legal cannabis can help cope with the opioid crisis has generated a lot of hope and excitement.
Opioid abuse has declined in recent years, as cannabis use has increased, as many states have liberalized their marijuana laws.
On the basis of recent research, some advocates have promoted this link, claiming that easier access to marijuana reduces opioid consumption and, as a result, overdose deaths.
A new study calls for caution. Sometimes appearances – or statistics – can be misleading.
Why people were so optimistic
It is plausible that marijuana can help reduce pain. Systematic reviews show that certain compounds in marijuana or cannabinoids produced by synthesis do so, at least under certain conditions. For example, some people who might otherwise look for opioid analgesics might use marijuana for medical purposes.
In 2014, a study published in JAMA Internal Medicine suggested that liberalization of marijuana laws could ease the opioid crisis.
The study focused on the years 1999 to 2010, during which 10 states set up marijuana programs for medical purposes. He compared changes in the rates of opioid analgesic deaths in states that have adopted marijuana laws for medical purposes with those who have not yet done so. The results? The researchers found that laws were associated with a nearly 25% drop in the death rate from opioid analgesics.
Since the publication of the JAMA study, others have produced similar results. One of the networks published at the Social Science Research Network last fall found that counties with medical marijuana dispensaries had up to 8% fewer deaths related to medical marijuana. opioids in non-Hispanic white men and 10% fewer deaths related to heroin.
Other studies have documented the marijuana laws associated with reduction of prescription opioids in Medicaid and Medicare.
Why should you be skeptical
None of this proves that the liberalization of marijuana causes reduction in opioid-related mortality, as pointed out by the authors of the 2014 JAMA study.
Correlation does not mean causality, of course. A particular challenge in interpreting correlations in the social sciences has its own name – the The ecological error. It is the erroneous conclusion that the relations observed at the broader level (such as the state or the region) are necessarily also at the individual level.
"Relationships may be strengthened, weakened, or even reversed when you move from the individual to the global level," said Mark Glickman, Senior Lecturer in Statistics at Harvard. This was documented in a classic article in 1950 and underlies many erroneous conclusions of the research.
A new study has resumed the analysis published by JAMA with more data. His findings cast doubt on the idea that marijuana for medical purposes helps reduce the number of opioid deaths – at least as far as we can judge with state-level data.
Between 2010 – the latest year of analysis in the JAMA study – and 2017, 32 more states have legalized marijuana for medical purposes, and eight legalized recreational uses. A new study published in the Proceedings of the National Academy of Sciences (PNAS) re-evaluated the relationship between these laws and opioid deaths using the same approach as the JAMA study, but by extending the years of analysis until 2017.
Over the years analyzed in the JAMA study, from 1999 to 2010, the new P.N.A.S. study results in similar results: the legalization of marijuana for medical purposes was associated with a reduction in the number of overdose deaths from opioid analgesics. But in a thorough analysis until 2017, the results were reversed – the laws are associated with 23% increase in the dead.
This does not necessarily mean that the laws have saved lives first and then, in later years, contributed to fatal overdoses.
"If there is a relationship between cannabis use for medical purposes and opioid overdose at the individual level, this type of study may not reveal it," said epidemiologist Chelsea L. Shover, lead author of PNAS study and a postdoctoral fellow at the Stanford School of Medicine.
Mr. Glickman said, "All of these studies can lead to potential biases. As states liberalized their marijuana laws, they could have changed other policies that also impact on opioid overdoses. We risk being misled by analyzes that also do not take into account these overdoses.
For example, efforts to expand the treatment of opioid abuse could reduce the number of deaths. Or imprison more opioid users could increase it, because studies have shown that overdoses are most likely after a stay in prison.
Other evidence suggests that it is unlikely that easier access to marijuana could significantly reduce the mortality rates of opioid analgesics. On the one hand, marijuana users for medical purposes only account for about 2.5% of the adult population, a small proportion of the 38% who receive a prescription for an opioid analgesic each year .
On the other hand, some works cast doubt on the idea that marijuana for medical purposes is substituting for opioids. One study showed that there was a positive correlation between marijuana use for medical purposes and the misuse of prescription medications, including painkillers.
Another revealed that patients on opioid analgesics who also used marijuana for medical purposes took higher doses of opioids than those who did not use them. And another study found that marijuana use tends to increase the chances of developing an opioid use disorder.
"Given what we know about research, we should disassociate our thinking about medical cannabis and opioid overdoses," said Dr. Shover. "However, there are other ways to solve the opioid crisis."
Easier and more legal ways to get marijuana for medical (and even recreational) purposes can have many benefits. But we must temper the enthusiasm that the reduction of opioid deaths is one of them.