The prospect of patient-oriented prescription drug labeling has focused increased attention on the effectiveness of written information for the consumer. Studies which have evaluated the effects of written prescription drug information in a patient population are reviewed. Several studies indicate that written information can be effective in improving patient compliance with regimens for antibiotic therapy. However, for drugs used on a long-term basis, written information as a sole intervention has not been shown to be sufficient for improving patient compliance. Patient knowledge of less commonly known information, such as precautions, side effects, or special directions is frequently improved by written information. Listing a drug's side effects has not been shown to increase the reported experience of side effects; however, one study suggests that patients may be more willing to report side effects to a health professional if they are listed in the written information. The trend for recent studies has been to focus on the "milieu" in which written information is provided or to systematically vary structural features of the information in order to improve the quality of drug communications.