A new study of vaping-related lung injuries in California reinforces the evidence implicating black-market cannabis products, even in states that have legalized the production and distribution of marijuana for recreational use. In a sample of 160 patients, just 9 percent reported vaping only nicotine—a claim that is doubtful in the absence of blood or urine testing. Just 1 percent of the patients who reported vaping THC identified a state-licensed retailer as the source of the products they used.

In this study, which was published last Friday in JAMA Internal Medicine, 75 percent of the admitted THC vapers said they obtained the products from informal sources. Among the 25 percent who initially said they had bought vapes from legal sources, just one patient named a licensed retailer. The rest either could not name their sources or said they bought cannabis products from pop-up shops, other individuals, or from a storefront that was not listed in the Bureau of Cannabis Control's database of licensees.

Although licensed retailers have been selling marijuana to recreational consumers in California since the beginning of 2018, illegal dealers still account for about three-quarters of sales, largely because high taxes, burdensome regulations, licensing delays, and local bans have made it difficult for legal merchants to compete with the black market. This study suggests that the black market also accounts for nearly all of the products used by people with vaping-related lung illnesses.

The researchers, who work for the California Department of Public Health and the U.S. Centers for Disease Control and Prevention (CDC), analyzed 87 vaping products from 22 patients, 49 of which contained cannabinoids. Eighty-four percent of the cannabis products contained vitamin E acetate, a diluting and thickening agent that has been strongly linked to the lung disease outbreak, which included 2,807 cases and 68 deaths as of February 18. None of the nicotine liquids contained that additive. An October study by California's Anresco Laboratories found vitamin E acetate in 60 percent of the illegal cannabis products the company tested but none of the legal products.

"This report—the first to our knowledge to describe cases in a state with a legal adult-use (recreational) cannabis market—appears to confirm patterns of clinical findings and vaping practices previously reported in other states and nationally," the researchers say. "Although California has a legal adult-use cannabis market, the majority of affected patients reported using THC-containing products obtained from informal sources, such as friends or acquaintances or unlicensed retailers. In addition, most THC-containing products tested contained [vitamin E acetate], which has recently been identified in both clinical and product samples from patients with [vaping-related lung injuries]."

Given that nearly all of the THC vapers seem to have used black-market products, "the majority" is an understatement. Furthermore, 91 percent of the patients reported vaping cannabis extracts, and the actual percentage is probably higher, since people may be reluctant to admit consuming black-market marijuana products. The CDC has found that people who claim to have vaped only nicotine generally test positive for THC. Yet the authors of the JAMA Internal Medicine study reiterate the California Department of Health's recommendation that "individuals refrain from using any vaping or e-cigarette products" (emphasis added), although they note that "THC-containing products from informal sources" are especially risky.

The warning against any sort of vaping is hard to square with the evidence, which overwhelmingly implicates "THC-containing products from informal sources." The California Department of Public Health's advice is not just misleading but irresponsible when it comes to legal nicotine vaping products, which are indisputably far less hazardous than conventional cigarettes. The CDC, by contrast, is now recommending that people "not use THC-containing e-cigarette, or vaping, products, particularly from informal sources like friends, family, or in-person or online dealers." It adds that "adults using nicotine-containing e-cigarette, or vaping, products as an alternative to cigarettes should not go back to smoking."