BACKGROUND: Anamorelin, a ghrelin receptor agonist, has recently been used to treat cachexia in patients with pancreatic cancer (PC). Although it was accepted in Japan for advanced PC for the first time in the world in 2020, its efficacy and safety were not fully tested. Thus, we sought to determine the safety and efficacy of anamorelin in patients with inoperable and relapsed PC. METHODS: We prospectively enrolled patients with inoperable and relapsed PC who had started anamorelin, lost their appetite, and met the criteria for cachexia. Appetite, body weight (BW), and muscle weight were measured at 0, 1, 2, 3, and 4 months. Characteristics and survival rates were compared between those who demonstrated anamorelin efficacy and those who did not. RESULTS: Out of the 45 patients studied, 31 continued anamorelin for 1 month and 20 for 4 months. After 1 month, appetite improved significantly (+1, range 0-4, P<0.001). BW (+1.8 kg, IQR 0.13-3.08, P<0.05) and muscle weight (+0.9 kg, IQR -0.05-2.6, P<0.05) showed significant increases. At 4 months, the increase in appetite, BW, and muscle weight remained stable. Patients who showed anamorelin effectiveness lived significantly longer than those who did not (366 106 days, respectively). CONCLUSIONS: In inoperable and relapsed PC, anamorelin may be more effective in patients with a better overall condition and is associated with longer survival. To improve patient outcomes, appetite and BW must be monitored regularly and anamorelin treatment should begin early.