Anorexia, cachexia, and resultant weight loss are major clinical problems in a substantial proportion of patients with advanced cancer. Effective means of alleviating these problematic symptoms are lacking. Extensive clinical data demonstrate a weight enhancing effect for the serotonin antagonist, cyproheptadine, in several clinical situations. In addition, sound basic research suggests that cyproheptadine may be helpful in patients with cancer anorexia/cachexia. Because of this, the authors performed a randomized, placebo-controlled, double-blinded clinical trial using cyproheptadine, 8 mg orally three times a day in 295 patients with advanced malignant disease. Patients assigned to cyproheptadine had less nausea (P = 0.02), less emesis (P = 0.11), more sedation (P = 0.07), and more dizziness (P = 0.01) than placebo patients. Patients' appetites, measured by serial patient-completed questionnaires, appeared to be mildly enhanced by cyproheptadine. Unfortunately, cyproheptadine did not significantly abate progressive weight loss in these patients with advanced malignant disease; patients assigned to cyproheptadine lost an average of 4.5 pounds per month compared to 4.9 pounds per month for patients assigned to a placebo (P = 0.72).