Polyphagia is extreme, intense hunger. Hypoglycemia is a common cause if you haven’t eaten all day. If your thyroid gland makes too much thyroid hormone, satiety signals can fail. PMS, anxiety, depression, and stress can all change eating habits and food cravings. In diabetes, when insulin can’t help cells take up glucose, they become starved for energy. Some drugs and Kleine-Levin syndrome, a rare neurological disorder, can also cause polyphagia.