Getting up in the morning with a bitter mouth may be a precursor of cancer, but cancer is not common. There are many causes of getting up in the morning with a bitter mouth, so the cause needs to be clarified and treated accordingly. Generally, if you feel bitter in your mouth for a short period of time, it may be related to your diet the day before, such as eating grapefruit, oranges or drinking coffee or tea, which may cause bitterness in your mouth the next morning. However, if the bitterness persists for a longer period of time or even accompanied by symptoms such as severe abdominal pain after eating fatty food, it is necessary to be alert to gallbladder diseases such as cholecystitis and cholelithiasis; digestive system diseases such as peptic ulcer, enteritis, gastritis and functional dyspepsia may cause abdominal flatulence and make one’s mouth bitter; cancer, such as oral cancer, stomach cancer and breast cancer, may also cause the phenomenon. In addition, lack of attention to oral hygiene or oral inflammation can also cause patients to have the corresponding symptoms. When patients have the symptom of bitter mouth in the morning, if it lasts for a short time, they can observe whether the symptom is relieved after eating lightly and cleaning the mouth; if it is not relieved or lasts for a long time, they should promptly go to the gastroenterology department of the hospital for consultation.