These symptoms can be mild or severe and are not experienced by all users. Side effects occur more frequently with high doses and long-term treatment and most commonly involve the gastrointestinal system. Aspirin use can cause ulcers, stomach bleeding, and in some cases perforation of the stomach (Kwok and Loke, 2010). This is due to the drug's interaction with COX-1 in the gastrointestinal tract. COX-1 is important for the maintenance of the gastric mucosa, and when the enzyme is deactivated by regular use of the drug, a thinning of the mucus occurs which protects the stomach from gastric juices, causing the side effects mentioned above. Other side effects include, for example, heartburn or indigestion, abdominal cramps or discomfort, dizziness, nausea or vomiting, swelling of the mouth and throat, and symptoms of an allergic reaction. In any case, the use of the drug should be stopped immediately and a doctor should be consulted