Pain under the ribs on the left side of the stomach can be caused by inflammation of the stomach or by a gastric ulcer, which can present with pain in the upper abdomen and loss of appetite and needs to be actively corrected. If it is caused by gastric ulcer, you can follow medical advice to use acid-suppressing and stomach-protecting drugs, such as omeprazole, and usually pay attention to strengthening nutrition, quitting smoking and limiting alcohol, and regular work and rest.