It is premature to expand access to medicinal cannabis in hopes of solving the US opioid crisis

Abstract

It is premature to expand access to medicinal cannabis in hopes of solving the US opioid crisisThere is very weak evidence to support the claim that expanding access to medical cannabis will reduce opioid overdose deaths in the United States.All human beings are susceptible to confirmatory bias, in that we are inclined to uncritically accept evidence that accords with our pre-existing beliefs [1]. A good example is the preparedness of some researchers to accept weak evidence that increased access to medical cannabis in the United States has reduced opioid overdose deaths in that country [2].The evidence for this hypothesis is very weak: ecological studies showing a correlation over time between the passage of medical cannabis laws and decreasing opioid overdose death rates in US states [3]. There would no doubt have been a much more critical response to these studies if they had found that opioid overdose deaths increased at a faster rate in states with medical cannabis laws.Ecological studies share two fundamental weaknesses: (1) they do not show directly that it is increased medical cannabis use in these states that has reduced opioid use in individuals and (2) they have limited capacity to control for the effects of important differences in the characteristics of states with and without medical cannabis laws that may explain the trends.The first is an inherent weakness of all ecological studies. It is why they are accorded so little weight in evaluating evidence for causal hypotheses [4]. Ice cream sales and the number of drownings are correlated positively, but eating ice cream does not cause drownings. Rather, sales of ice cream are higher in the warmer summer months when more people go swimming.Some better-controlled studies have shown that the relationship between medical cannabis laws and opioid overdose deaths persists when controlling, as best they can using state-level data, for differences between states that do and do not have medical cannabis laws. These have included state differences in: income, population, education and ethnicity, prescription monitoring programmes that aim to reduce access to opioids and naloxone distribution for onlookers to reverse opioid overdoses [5][6][7].No studies so far, however, have controlled for the effects of several policies that are likely to affect opioid overdose deaths for the better or worse. The former includes increased access to methadone-and buprenorphineassisted treatment for opioid dependence [8], both of which are likely to reduce overdose risk. The latter includes public policies that are likely to increase overdose deaths; namely, increased imprisonment of opioid users because their risk of overdose death increases dramatically after they leave prison [9].The lower rate of increase of opioid deaths in states with medical cannabis laws could be explained if the latter policies were correlated with whether or not a state had passed medical cannabis laws. It is plausible that they are, because politically conservative US states are less likely to pass m...

Access to medical cannabis is expanding across North America regardless of the opioid crisis—why not study if it could help?

“…A claim that the 'latest scientific evidence indicates' a reduction in opioid overdoses following increased cannabis accessibility [1] was labelled 'a good example' of confirmation bias by an Addiction editorial [2] that saw only 'very weak' evidence for the assertion. We disagree, suggest additional causal mechanisms and clarify remaining research gaps.…”

“…While well aware of the limitations of ecological research, as described by the authors [1], we also recognize the value that ecological studies can provide in sparking new avenues of research. This is especially the case for cannabis science, an area of inquiry whose development has long been stunted artificially as a result of the substance's prohibited status.…”

“…In a recent editorial [1], Hall and colleagues argue that research exploring the effect of medical cannabis laws on opioid use and overdose is underdeveloped and insufficient to support the expansion of medical cannabis in response to the US opioid crisis. A commentary we published in a Canadian media outlet [2] was the anchor for the authors' hypothesis that some scientists are prepared to 'accept weak evidence that increased access to medical cannabis in the US has reduced opioid overdose deaths in that country' [1].…”

“…A commentary we published in a Canadian media outlet [2] was the anchor for the authors' hypothesis that some scientists are prepared to 'accept weak evidence that increased access to medical cannabis in the US has reduced opioid overdose deaths in that country' [1].…”

Medical and non‐medical cannabis use and risk of prescription opioid use disorder: Findings from propensity score matching

“…These ecological studies share the same problem of ecological fallacy , which use findings derived from ecological population data to imply individual‐level associations. To fill this knowledge gap, Olfson et al .…”