Omeprazole capsules generally do not cause black stools, black stools need to consider other causes, such as food, drug-related, may be caused by upper gastrointestinal bleeding. Omeprazole capsule is a proton pump inhibitor, has the effect of inhibiting the secretion of gastric acid, generally does not cause black stool, in some gastrointestinal bleeding caused by black stool also need to apply omeprazole treatment. Black stool may be related to diet and medication. For example, the use of black sesame, black beans, animal blood products and other foods can cause black stools, taking bismuth, iron and other drugs can also cause black stools. Black stools may also be caused by diseases, which are common in upper gastrointestinal bleeding caused by various reasons, such as bleeding from peptic ulcer, rupture and bleeding from esophagogastric fundic varices of cirrhosis, tearing of cardia mucosa, and bleeding caused by gastric cancer. If you have black stools, you should go to the hospital for treatment under the guidance of a doctor after excluding physiological causes.