Bitterness in the mouth after waking up in the morning may occur occasionally in normal people, mostly caused by eating too much dinner or eating too much spicy and stimulating food. Sometimes bitterness in the mouth after waking up can also occur after exertion, insufficient sleep and rest, smoking, alcoholism, snoring, sleeping with the mouth open, etc. Bitterness in the mouth is often caused by diseases such as poor gallbladder function, cholecystitis, cholelithiasis and other gallbladder diseases, and some of the bile secreted in the duodenum will reflux into the stomach due to pathogenic factors. Patients with poor gastric motility and inflammation in the esophagus can also cause bile to reflux into the stomach and cause bitterness in the mouth. Patients with oral diseases such as gingivitis, dental caries and dental calculus can cause bitterness and bad breath after waking up in the morning. In short, the causes of bitter mouth are more complex, and if the symptoms of bad breath are more serious, it is recommended that patients go to the hospital for diagnosis and timely treatment.