Getting up in the morning with a bitter mouth is mainly due to bile reflux into the stomach, causing symptoms caused by bile reflux gastritis. Biliary reflux gastritis can be divided into primary and secondary. Biliary reflux gastritis is caused by surgery that destroys the pylorus between the stomach and duodenum, which is the natural barrier of the human body. Once the bile in the duodenum is surgically removed or because of other surgical factors it can reflux directly into the stomach, causing the destruction of the gastric mucosa by bile and causing bitterness in the mouth. The causes of primary bile reflux gastritis are complex. Common causes include hepatobiliary and pancreatic diseases, such as hepatitis, cholecystitis, gallbladder stones, pancreatitis or gastritis. There are also medications, long-term use of some drugs, such as aspirin or other drugs that cause gastrointestinal dysfunction, and bile can reflux into the stomach. Mental factors including anxiety and emotional stress lead to gastrointestinal dysfunction, which can also cause bile reflux. Dietary habits and lifestyle habits, such as snacking, skipping breakfast, smoking and alcohol abuse, can cause bile reflux, which can also cause a bitter mouth in the morning.