Objectives. To examine US adults’ reactions to health warnings with strong versus weak causal language. Methods. In 2018, we randomly assigned 1360 US adults to answer an online survey about health warnings for cigarettes, sugar-sweetened beverages, or alcohol. Participants rated 4 warning statements using different causal language variants (“causes,” “contributes to,” “can contribute to,” and “may contribute to”) displayed in random arrangement. Results. Most participants (76.3%) selected the warning that used “causes” as the 1 that most discouraged them from wanting to use the product. “Causes” was also selected most often (39.0% of participants) as the warning that participants most supported implementing. By contrast, most (66.1%) chose “may contribute to” as the warning that least discouraged them from wanting to use the product. We found few demographic differences in these patterns. Conclusions. Warnings with stronger causal language are perceived to be effective and are supported by the public.