Diarrhea after drinking coffee may be caused by excessive coffee intake, drinking on an empty stomach or gastrointestinal diseases. 1. Excessive coffee intake: Usually, coffee contains substances that stimulate the secretion of gastric acid, which will affect the body in case of excessive intake, and diarrhea will occur in serious cases. 2. Drinking on an empty stomach: coffee is irritating to the gastric mucosa when drinking on an empty stomach, which in the long run will cause damage to the gastrointestinal mucosa, leading to gastritis, gastric ulcer and other diseases. 3. Gastrointestinal diseases: If there are patients with gastrointestinal digestive diseases, such as chronic gastritis, peptic ulcer and other diseases, the digestive function of the spleen and stomach will be reduced, and there will be abdominal pain after drinking coffee. Diarrhea after drinking coffee may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.