There are many causes of bitter mouth, such as oral diseases, digestive system diseases, taking drugs and other factors. 1. Oral diseases: Common diseases include tooth decay, gingivitis, pulpitis, mouth ulcers, and lingual inflammation, which may cause abnormal secretion of fluids, thus leading to the symptom of bitter mouth. 2. Digestive system diseases: common bile, reflux gastritis, cholecystitis, gallstones, chronic hepatitis, chronic gastritis, there may also be a bitter mouth. 3. Taking medication: after taking certain medications, the medication may remain in the mouth, or the adverse reaction of the medication may lead to the symptom of bitter mouth. There may be other reasons for bitter mouth, you need to go to the hospital for examination and treatment as prescribed by the doctor.