The social norms approach predicts that campaign messages providing true normative information about widely misperceived health behaviors will reduce the gap between distorted perceptions versus actual practices and consequently reduce behaviors based on exaggerated norms. Formative evaluation of messages designed to effectively convey true norms informed by social judgment theory (SJT) should measure the boundaries of the latitudes of acceptance, noncommitment, and rejection for normative information. This study found that these latitudes were significantly different from one another in believability. SJT predicts that a campaign based on a norm falling in the latitude of noncommitment will be likely to be effective. A series of messages using the true norm, which fell within the latitude of noncommitment, were part of a campaign. The gap in perceived versus actual drinking and the difference in perceived number of drinks was reduced, while self-reports of consumption of five or fewer drinks increased significantly.