Coffee ground vomitus refers to a particular appearance of vomit. Within organic heme molecules of red blood cells is the element iron, and when this iron has been exposed for some time to gastric acid, it becomes oxidized. This reaction causes the vomitus to look like ground coffee. Coffee-ground vomitus is a classic sign of upper gastro-intestinal bleeding. A peptic ulcer, for example, may bleed into the stomach and produce coffee-ground vomitus. There are many causes that can result in this reaction, with use of NSAIDs (Non-Steroidal Anti-Inflammatory Drugs) and SSRIs (Selective Serotonin Reuptake Inhibitors) being particularly common. These drugs can interfere with the stomach's natural defenses against the strongly acidic environment, causing damage to the mucosa that can result in bleeding. Therefore it is recommended that these class of drugs should be taken with food or on a full stomach. Certain types of illnesses, however, can cause this type of vomiting, and in these cases medical attention is required immediately.