This is a moment for legitimate alarm at the intersection of two distressing but distinct epidemiological patterns involving e-cigarettes (“vaping”): an increase in vaping among youth and a sudden outbreak of acute lung injuries and deaths in the United States, associated most strongly with vaping tetrahydrocannabinol (THC), the main psychoactive compound in cannabis. Discussions of vaping, however, often neglect distinctions between nicotine and THC; between adults and youth; and between products obtained through the retail and black markets. [...]