Diarrhea is also known as diarrhea and a few people experience diarrhea after drinking black coffee. After drinking coffee, diarrhea is common in the following cases. 1. Drinking coffee on an empty stomach: the caffeine in coffee can stimulate the secretion of gastric acid, and drinking on an empty stomach has a more obvious stimulating effect on gastric acid, so some people will have abdominal pain or even diarrhea after drinking coffee on an empty stomach. 2. Excessive drinking: coffee can promote gastrointestinal peristalsis, drinking too much coffee at one time, gastrointestinal peristalsis increases, can increase the number of bowel movements, and even diarrhea. 3. Allergy to coffee: some people will experience abdominal pain and diarrhea every time they drink coffee, and the symptoms will get better after they stop drinking coffee, which may be due to allergy to caffeine, and it is recommended that people in this situation should avoid eating caffeine-containing foods and beverages. If you have diarrhea after drinking black coffee, consult a doctor as soon as possible to avoid delaying your condition.