Ninety-eight adults treated with erythromycin for a variety of illnesses were randomized to two groups: the informed group received patient education about drug side effects, and the uninformed group were given no such information. Overall, 10% of the uniformed and 8% of the informed group felt the erythromycin bothered them in some way. There were no significant differences in the occurrence of various individual side effects. Compliance with therapy and the results of treatment were the same for both groups. In this study, informing patients about side effects of therapy did not have any detectable adverse effects.