Bitter mouth in the morning is mainly caused by bile reflux bile reflux gastritis, the cause is divided into primary bile reflux gastritis and secondary bile reflux gastritis. Secondary bile reflux gastritis is caused by surgery that destroys the pylorus, which is a natural anatomical structure. Once removed, bile can reflux from the duodenum into the stomach on its own, leaving the natural barrier unprotected and leading to a bitter taste in the mouth. The causes of primary and secondary bile reflux gastritis are complex, and commonly include hepatobiliary and pancreatic diseases, mainly cholecystitis, pancreatitis, diabetes mellitus, as well as peptic diseases including peptic ulcers and gastritis. There are also psychiatric factors, such as emotional stress, anxiety and poor sleep, which can cause bile reflux. There are also medications that can cause bile reflux, which can lead to bitter mouth symptoms. Smoking, long-term alcohol abuse, bad dietary habits, including skipping breakfast, love to eat late-night snacks, love to eat high-fat food, eating too much, obesity can induce bile reflux caused by bitter mouth in the morning.