Background Conspiracy theories about the origins of COVID-19 are wide-spread and have even been propagated by highly ranked state officials and politicians in the U.S. Health authorities have cautioned that such theories, although not questioning the existence of the pandemic, may increase the spread of the virus by reducing people’s efforts to socially distance. Methods We test this proposition empirically using longitudinal survey data collected at five time points during the early outbreak of the virus in the U.S. (N = 403). ResultsMultivariate growth curve analyses showed that, although conspiracy beliefs decreased and social distancing increased over time, people holding more conspiracy beliefs at the beginning of the pandemic showed the lowest increase in social distancing. Moreover, cross-lagged analyses demonstrated that people who reported more conspiracy beliefs at any wave tended to report less social distancing at the following wave. ConclusionsOur findings show that COVID-19 conspiracy theories pose a significant threat to public health as they may reduce adherence to social distancing measures.Keywords Conspiracy theories, COVID-19, social distancing, longitudinal