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
References:
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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