Bitter mouth in the second half of the night may be a result of poor oral hygiene, or may be suffering from certain diseases, such as gallstones, cholecystitis, etc., need to analyze specific problems. 1. Poor oral hygiene: For example, if you do not brush your teeth before going to bed, there are food residues in the mouth, or there is soft dirt on the surface of the teeth, etc., due to the propagation and growth of bacteria, the phenomenon of bitter mouth in the second half of the night will occur. Generally, it can be improved after improving oral hygiene, and no special treatment is needed. 2. Suffering from gallstones or cholecystitis: mainly due to the increased pressure of the biliary system, bile can not be discharged smoothly, then at night when resting, there will be bile reflux, at this time, if the bile reaches the oral cavity, there will be the phenomenon of bitter mouth in the second half of the night, often accompanied by nausea, vomiting and other manifestations. If the bitter mouth in the second half of the night can not be relieved by cleaning the mouth, it is recommended to go to a regular hospital to get a clear diagnosis as soon as possible, and follow the doctor’s instructions for treatment.