The political aspects of medical cannabis are undeniable. The legalization of cannabis for recreational purposes had no traction with American politicians or voters until it was promoted as a miracle drug. With that widespread promotion medical cannabis is now legal in 33 states and recreational cannabis is legal in ten. The legalization arguments also suggested that the US was behind other countries of the world when there are only two countries – Canada and Uruguay – where it is completely legal for medical or recreational sale and purchase. In the world, 22 of 195 countries have legalized medical cannabis with widely varying restrictions on its use. The Netherlands is often cited as an example of recreational cannabis use, but most Americans don’t realize that it is illegal for recreational use and tolerated for use and sale only in specially licensed coffee shops. The promotion of cannabis as a solution to the opioid overuse and chronic pain problems can be seen as an extension of the political arguments for legalization that outpace any science to back them up.
There was probably no greater hype about the purported benefits of medical cannabis than early data suggesting that it might decrease the rate of opioid overdoses (1). The sequence of events was supposed to be opioid users tapering off of opioids or using lower equivalent amounts because of medical cannabis use. The original study covered the time period from 1999-2010 and suggested that states with medical cannabis laws had a lower mean opioid overdose mortality and that the annual rates of overdose progressively decreased over time. The authors conclusion was: “Medical cannabis laws are associated with significantly lower state-level opioid overdose mortality rates.”
Despite the usual caveats suggested by the authors in the original study the results of that study were heavily hyped by all cannabis promoters as was the discussion of many Internet forums. The lay press, public, and politicians saw it as another reason to promote medical cannabis and recreational cannabis by association.
A study came out today in PNAS (2), that is an extension of the original data and it no longer comes to the same conclusion. In this new study the authors replicated the opioid mortality estimates from the original study but when the data was extended from 2010 to 2017 – the improved opioid overdose mortality rates not only did not stay constant but they reversed themselves to that they were now on the average from -21% to +23%. They provide an even more valuable analysis of this effect as spurious rather than a true positive or negative effect based on the low penetration of medical cannabis in the population at large (2.5%). The authors focus on the problem of ecological fallacy – that is conclusions about individuals are drawn from aggregate data across the entire population.They point out that the states with the medical cannabis laws have a number of characteristics separating them from other states. A recent good example of this fallacy was the New England Journal of Medicine (3,4) report that per capita chocolate consumption correlated with the number of Nobel Laureates in a particular country.
This is a valuable lesson in scientific analysis. The political approach to the problem is all that most of the public sees. That approach is to grab any information that seems to agree with your viewpoint and run with it. Big Cannabis and cannabis promoters have been doing this for almost 20 years now. The process of science on the other hand is slower and more deliberate. It is not a question of a right answer but a dialogue that hopefully produces the right pathway. The authors of this study have added a lot to the dialogue about cannabis but also statistics and how statistical descriptions may not be what they seem to be.
George Dawson, MD, DFAPA
1: Bachhuber MA, Saloner B, Cunningham CO, Barry CL. Medical Cannabis Laws and Opioid Analgesic Overdose Mortality in the United States, 1999-2010. JAMA Intern Med. 2014;174(10):1668–1673. doi:10.1001/jamainternmed.2014.4005 (full text)
2: Shover CL, Davis CS, Gordon SC, Humphreys K. Association between medical cannabis laws and opioid overdose mortality has reversed over time. First published June 10, 2019 https://doi.org/10.1073/pnas.1903434116 (full text)
3: Messerli FH. Chocolate consumption, cognitive function, and Nobel laureates. NEngl J Med. 2012 Oct 18;367(16):1562-4. doi: 10.1056/NEJMon1211064. Epub 2012 Oct 10. PubMed PMID: 23050509.
4: Pierre Maurage, Alexandre Heeren, Mauro Pesenti, Does Chocolate Consumption Really Boost Nobel Award Chances? The Peril of Over-Interpreting Correlations in Health Studies, The Journal of Nutrition, Volume 143, Issue 6, June 2013, Pages 931–933, https://doi.org/10.3945/jn.113.174813
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