Bitter mouth after waking up in the morning may be caused by smoking, oral problems, diabetes, gastrointestinal diseases and so on. 1. Smoking: If you are under a lot of stress and have the habit of smoking, you will be able to relieve your stress by smoking, which will lead to bitter mouth after waking up in the morning. 2. Oral problems: Bitter mouth after waking up in the morning may be caused by oral problems, including gingivitis, periodontitis and other diseases, mainly due to the propagation of bacteria in the oral cavity, the emergence of bitter mouth. 3. Gastrointestinal flora imbalance: when patients with long-term constipation or diabetes and other chronic diseases, resulting in patients with intestinal flora imbalance, which leads to patients with a bitter mouth early in the morning. 4. Gastrointestinal diseases: when the patient has gastroesophageal reflux, bile reflux gastritis, it will cause the situation of bitter mouth in the morning, the food in the stomach and intestines to stay longer, the stomach gas from the mouth, resulting in bitter mouth. It is recommended that patients go to the hospital for examination, according to the doctor’s method to actively cooperate with the treatment, life should do a good job of oral cleaning, regular work and rest, balanced diet.