Twitter, Facebook, and other social media display the combined opinion of users as collective opinion. The purpose of the work reported here was to examine how collective opinion might influence the perceived truthfulness and the sharing likelihood of health-related statements on social media. Experiment 1 revealed that, when evaluating the truthfulness of a statement, participants adopted the collective truthfulness rating associated with the statement. Similarly, Experiment 2 showed that the likelihood that participants would share a statement followed the collective sharing likelihood associated with the statement. These social impacts were extensive, taking place for statements perceived as true, debatable, and false. These results contribute new insights into how people perceive and share information on social media as well as how collective opinion might affect the quality of information on social media.