A prospective online study, consisting of 203 participants ages 18 and older who smoked waterpipe (hookah) within the last 30 days, examined how brief messaging about harms of burning charcoal to heat waterpipe tobacco (shisha) influenced knowledge of toxicants released by using charcoal and perceived harms of using charcoal. Participants were randomized to either a control or to an educational arm that reviewed toxicants released by burning charcoal and the health consequences. Participants in the educational relative to the control arm perceived charcoal as more harmful, were more knowledgeable of toxicants released by burning charcoal, and expressed a stronger desire to quit. Effects were sustained a week later. Brief messages about the harms of burning charcoal were effective and may be used to educate the public about the harms of waterpipe tobacco smoking.