Diarrhea after lunch may be due to irritable bowel syndrome, food poisoning, indigestion and other diseases, need to take dietary adjustments, medication, etc. for the cause of the disease. 1. Irritable bowel syndrome: common symptoms include abdominal pain, diarrhea and so on. Patients need to follow the medical advice to apply antispasmodic agents, such as scopolamine, etc., and antidiarrheal agents, such as loperamide, compound phenethylpiperidine, etc., as well as probiotics and other micro-ecological agents. Patients should try to avoid eating foods that induce this disease such as alcohol, sweet potatoes, etc., and adjust the diet structure. 2. Food poisoning: mostly considered as gastrointestinal food poisoning, the main symptoms include diarrhea, nausea, vomiting and so on. Patients need to follow the doctor’s instructions to apply antidiarrheal drugs such as montelukast, as well as antihistamines such as diphenhydramine and loratadine. If a bacterial infection is present, antibiotics such as amoxicillin and ceftriaxone are also prescribed. For patients with severe diarrhea and abdominal pain, temporary fasting and bed rest are required to facilitate the recovery of gastrointestinal function. 3. Dyspepsia: typical symptoms include postprandial fullness, diarrhea, reflux and so on. Patients need to apply proton pump inhibitors such as omeprazole, lansoprazole, etc. Some patients also need to apply probiotics such as Bifidobacterium bifidum, Bacillus licheniformis, etc. in accordance with medical advice. Patients need to improve their lifestyle and develop good eating habits. There are more causes of constant diarrhea after lunch, and you need to go to the hospital and cooperate with the doctor to treat the original disease.