Diarrhea upset stomach may be caused by food factors, gastrointestinal inflammation, peptic ulcer and drug factors. 1. Food factors, a long time of bad eating habits, such as: alternating between too cold and too hot food, overeating, more oil, sandwich, etc., will lead to gastrointestinal mucosal malabsorption, which in turn causes diarrhea symptoms. 2. Inflammation of the gastrointestinal tract, if the gastrointestinal tract is inflamed to varying degrees due to bacterial or viral infections, it can also cause diarrhea and upset stomach. 3. Peptic ulcers, depending on the age and site of occurrence, including gastric ulcers and duodenal ulcers, etc. Due to the presence of ulcers, the digestive function will be affected, and then diarrhea will appear. 4. Drug factors, when taking drugs such as sodium phosphate, neostigmine and metformin due to underlying diseases, gastrointestinal discomfort may occur due to drug side effects. It is recommended to consult a medical professional in a timely manner.