Eighteen deaths have been reported in 15 states so far. Although officials said the exact cause behind the injuries has not been determined, most of the people who have suddenly fallen sick have reported using vaping products that contained THC.

“[Consumers] should not use vaping products containing tetrahydrocannabinol (THC), the primary psychoactive component of the cannabis plant,” the FDA announced Friday. “Additionally, consumers who choose to use any vaping products should not modify or add any substances such as THC or other oils to products purchased in stores and should not purchase any vaping products, including those containing THC, off the street.”