States that had recreationally legalized marijuana saw fewer cases of e-cigarette/vaping-related lung injury (EVALI) than states without such policies in 2019, researchers reported.

In states that had legalized recreational marijuana, the EVALI case rate averaged 1.7 per million population (95% CI 0.3-3.1), far lower than states where it's legal only for medical purposes (8.8 per million, 95% CI 5.1-12.5) or completely illegal (8.1 per million, 95% CI 4.1-12.0), reported Alex Hollingsworth, PhD, of Indiana University in Bloomington, and colleagues.

Moreover, the number of cases was significantly lower in states with legal recreational marijuana compared to those where it was not after adjusting for vaping rates (difference 7.2 cases per million, 95% CI -11.8 to -2.6, P=0.003), they wrote in a JAMA Network Open research letter.

"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," Hollingsworth told MedPage Today.

Although the specific cause of EVALI is uncertain, it has been linked to tetrahydrocannabinol (THC) vaping products containing vitamin E acetate, which are more commonly sold by illicit "street" vendors than by legal dispensaries.

The implications of these findings draw parallels with the Prohibition Era a century ago, wrote Scott K. Aberegg, MD, MPH, and two colleagues at the University of Utah School of Medicine in Salt Lake City in an accompanying editorial.

Just as many Americans in the 1920s resorted to poisonous alcohols such as methanol, e-cigarette users have turned to the black market to obtain THC-vaping products in light of legislation prohibiting marijuana use, Aberegg and colleagues noted.

But the editorialists didn't let the legal-cannabis states off the hook completely for EVALI. While marijuana legalization appears to have "protective local effects," there may also be "untoward collateral effects," they argued.

"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," they wrote, noting that "vitamin E acetate is often used to stretch" the THC in vaping liquids.

Despite the possibility of ecological fallacy or other confounding factors, these findings underscore "the complex realities of social movements and resulting legislation that may have unforeseen and unforeseeable public health consequences, for better and for worse, that are recognized only in retrospect," the editorial noted.

For the study, Hollingsworth and colleagues used CDC data to measure the number of EVALI cases occurring in 2019 across 50 states plus Washington, D.C. The prevalence of e-cigarette use and state populations were generated from 2017 CDC data.

States with recreational marijuana legalized had 7.1 fewer cases per million (95% CI -10.9 to -3.2, P<0.001) than medical marijuana states and 6.4 fewer cases per million (95% CI -10.4 to -2.3, P=0.004) than so-called prohibition states. The difference between medically legal and prohibition states was not significant.

States in all three categories had similar rates of vaping, with no association between rates of e-cigarette use and EVALI observed across states (difference -1.3, 95% CI -3.3 to 0.7, P=0.20).

As a cross-sectional study using aggregate state-level data, confounding is possible and the findings may not accurately convey trends at the individual level, Hollingsworth's group noted. Also, CDC data report a range of EVALI cases for each state, and the researchers used the midpoint of each state as the case rate.