People in states where recreational marijuana is legal were significantly less likely to experience vaping-related lung injuries than those in states where cannabis is prohibited, according to a new study published in an American Medical Association journal.

The finding seems to affirm what many reform advocates said during the peak of the e-cigarette or vaping product use-associated lung injury (EVALI) crisis last year. With thousands being hospitalized over EVALI, it became clear that contaminated vape cartridges were the source and that contamination was more common in illicit, unregulated markets where consumers can’t walk into retail stores and buy tested and labeled marijuana products.

By analyzing Centers for Disease Control and Prevention (CDC) data on EVALI cases, the prevalence of e-cigarette use and the population in each state from June 2019 to January 2020, researchers were able to confirm that.

The research letter, published by the JAMA Network Open on Monday, shows that states with recreational marijuana shops had 1.7 EVALI cases per million population compared to 8.1 cases per million in prohibition states. There was no statistically significant difference between criminalized and medical cannabis states, which experienced 8.8 cases per million population.

“The data suggest that EVALI cases were concentrated in states where consumers do not have legal access to recreational marijuana dispensaries,” the letter states. “This association was not driven by state-level differences in e-cigarette use, and EVALI case rates were not associated with state-level prevalence of e-cigarette use. One possible inference from our results is that the presence of legal markets for marijuana has helped mitigate or may be protective against EVALI.”

“Recreational marijuana states had among the lowest EVALI rates of all states.”

While the researchers said the reason for the association isn’t clear yet, they surmised that it’s “possible that in recreational states, people tend to purchase marijuana products at legal dispensaries, which may be less likely to sell the contaminated products that are thought to cause EVALI.”

That has been the working theory of many industry observers, who have argued that legalization is an important safeguard to public health by ensuring compliance with quality control standards in cannabis products. It should be noted, however, that there are select reports of instances where people seemed to develop a lung injury after obtaining marijuana vaping products from licensed dispensaries in Oregon.

“It appears states that have legal access to marijuana have lower rates of EVALI cases, which is consistent with the hypothesis that people have demand for marijuana products, and in states where they don’t have access to them in this regulatory fashion, they end up purchasing them elsewhere,” study co-author Alex Hollingsworth told MedPage Today.

NORML Executive Director Erik Altieri said the findings “come as little surprise.”

“In jurisdictions where cannabis is legally regulated, consumers gravitate toward the above-ground retail marketplace where they can access lab-tested products manufactured by licensed businesses,” he said. “Just like alcohol prohibition gave rise to the illicit production of dangerous ‘bathtub gin,’ marijuana prohibition provides bad actors, not licensed businesses, the opportunity to fulfill consumers’ demand—sometimes with tragic results.”

In a historical commentary on the new study also published by the American Medical Association Journal, a separate set of researchers drew a parallel to the era of alcohol prohibition—from which an underground industry of bootleggers emerged.

“Bootleggers fortified their distillates with methanol to increase apparent potency, causing blindness and death in unwary consumers,” they said, noting that industrial ethanol, which was exempt from prohibition, was sometimes used despite the fact that government officials directed it to be adulterated with poisonous substances to deter consumption. “The resulting concoctions, known as denatured alcohol, were responsible for thousands of deaths during the 14 years that Prohibition was in effect. The history of Prohibition thus serves as a cautionary tale about unintended and unforeseen consequences of legislation regulating substances that affect public health.”

“Bootlegging was rampant and criminal syndicates proliferated, fueling a wave of organized crime.”

Commentary: EVALI rates are lower in states that have legalized recreational marijuana. Is legalizing marijuana protective against EVALI as there is less incentive to dilute THC in states where raw THC material is readily available without legal risk? https://t.co/Bd5Z8wYbjQ — JAMA Network Open (@JAMANetworkOpen) April 7, 2020

EVALI similarly appears to be strongly associated with a specific contaminant in illicit markets, vitamin E acetate (VEA), which is used to dilute or stretch cannabis concentrates —”a scenario reminiscent of the unscrupulous bootleggers of the Prohibition era.”

“How could a state’s legalization of recreational marijuana inadvertently protect its citizens against EVALI? The obvious answer is that THC-containing vaping products in states where recreational marijuana is legal are uncontaminated with VEA. If so, another question follows: why would THC products in these states be less likely to be contaminated (ie, diluted) with VEA? One salient possibility is that there is less financial incentive to dilute THC concentrates in states where raw THC material is readily available without legal risk and compensatory markup.”

“If THC concentrates are transported from states where they are legal and can be relatively cheaply mass produced (like industrial ethanol stocks during Prohibition) to other states where they are illegal and must be guarded jealously as a rare and precious commodity, there may be a strong economic inducement to dilute them, thereby increasing profits. Thus, legalization of marijuana may have protective local effects but untoward collateral effects.”

President Trump also seemed to pick up on the failure of prohibition during a meeting on the vaping crisis last year. He acknowledged that simply banning the products wouldn’t work, as people would simply move on to the illicit market, where there aren’t regulations.

What’s worse, the conflict between state and federal marijuana laws actually inhibited research into how to address EVALI cases, complicating shipments of vaping specimens, a top CDC official said.

The same official also suggested that federal cannabis regulations could mitigate the vaping problem. Former Food and Drug Administration Commissioner Scott Gottlieb made a similar argument.

This story was updated to include comment from NORML.