Negative preconceived beliefs about the benefits of morphine use are frequently seen in hospitalized patients and may be associated with reports of severe pain, poor patient satisfaction, impaired rehabilitation, and possibly more chronic postsurgical pain. In some patients, providing information through instructive leaflets may modify negative beliefs that limit proper medication use. The purpose of this study was to determine whether the morphine-related information provided through leaflets during the postoperative period led to increased use of morphine and lower pain scores in patients using patient-controlled analgesia. One hundred patients scheduled for surgery were randomly assigned to the experimental (n = 53) or control group (n = 38). Patients included in the former group received detailed information on morphine; those in the latter group received only general information on postoperative acute pain. The results indicated that during the immediate postoperative period, morphine use was directly associated with pain intensity and satisfaction with pain management and inversely related with side effects. These results show that pain intensity is the most relevant issue in the decision to use morphine. Information leaflets did not change morphine consumption.