PURPOSE: Prior studies have suggested that melatonin, a frequently used integrative medicine, can attenuate weight loss, anorexia, and fatigue in patients with cancer. These studies were limited by a lack of blinding and absence of placebo controls. The primary purpose of this study was to compare melatonin with placebo for appetite improvement in patients with cancer cachexia. PATIENTS AND METHODS: We performed a randomized, double-blind, 28-day trial of melatonin 20 mg versus placebo in patients with advanced lung or GI cancer, appetite scores ≥ 4 on a 0 to 10 scale (10 = worst appetite), and history of weight loss ≥ 5%. Assessments included weight, symptoms by the Edmonton Symptom Assessment Scale, and quality of life by the Functional Assessment of Anorexia/Cachexia Therapy (FAACT) questionnaire. Differences between groups from baseline to day 28 were analyzed using one-sided, two-sample t tests or Wilcoxon two-sample tests. Interim analysis halfway through the trial had a Lan-DeMets monitoring boundary with an O'Brien-Fleming stopping rule. Decision boundaries were to accept the null hypothesis of futility if the test statistic z < 0.39 (P ≥ .348) and reject the null hypothesis if z > 2.54 (P ≤ .0056). RESULTS: After interim analysis of 48 patients, the study was closed for futility. There were no significant differences between groups for appetite (P = .78) or other symptoms, weight (P = .17), FAACT score (P = .95), toxicity, or survival from baseline to day 28. CONCLUSION: In cachectic patients with advanced cancer, oral melatonin 20 mg at night did not improve appetite, weight, or quality of life compared with placebo.