2019–2020 vaping lung illness outbreak

An outbreak of e-cigarette, or vaping, product use-associated lung injury (EVALI) began in 2019 among users of illegal, unregulated cannabis vaping products, almost exclusively in the United States. The first cases were identified in Illinois and Wisconsin in April 2019; as of 18 February 2020, a total of 2,807 hospitalized cases, including 68 deaths, had been confirmed. According to the U.S. Centers for Disease Control (CDC), "Vitamin E acetate is strongly linked to the EVALI outbreak...Evidence is not sufficient to rule out the contribution of other chemicals of concern, including chemicals in either THC or non-THC products".

Cases peaked in September 2019, and declined thereafter. The decline led CDC to stop reporting EVALI cases in February 2020, but as of December 2020, continued to monitor cases arriving in emergency departments. Some states continued to record new EVALI cases. As of January 2022, California had reported at least 40 cases diagnosed after February 2020. As of March 2022, EVALI cases continued to be diagnosed. At least 73 cases were diagnosed in Utah after February 2020.

CDC investigators identified direct exposure to chemicals present in illegal cannabis vaping products as the likely culprit, but did not rule out chemicals in nicotine vapes as possible causes. CDC: "No specific e-cigarette device or substance has been linked to all cases, and e-cigarettes include a variety of chemical and additives". 84% of patients studied by the CDC reported THC use. The majority of those affected were adults aged 18–34, the biggest cannabis vapers in the U.S.