Laboratory studies and anecdotal reports by users suggest that palpitations often follow the administration of marijuana or cocaine. Epidemiologic strategies are used to detect this association using interview data from 6702 household residents sampled and followed prospectively for a collaborative multi-site study of mental disorders in five U.S. communities. The lifetime data indicated that those who used marijuana and/or cocaine were much more likely to report an occurrence of palpitations than non-users. These relationships remained strong after statistical adjustment for cardiovascular disease risk factors such as gender, race and the use of sympathomimetic drugs other than cocaine. The greater risk was found among those who reported use of cocaine but not marijuana (estimated relative risk = 3.41, 95% confidence interval = 1.60-7.29, P less than 0.001).