COX-2 inhibitors are a special type of analgesic. Cyclooxygenase (commonly abbreviated as COX) is an enzyme that has an important role in starting an inflammation and pain. There are many different types of COX; the most common are known as COX-1 and COX-2. NSAIDs work by blocking COX. The problem with blocking all COX is that COX-1 is also used to regulate kidney function. Blocking COX-1 runs the risk of bleeding of the stomach, and reduction of the kidney function. COX-2 inhibitors only block COX-2, and do not have an effect on COX-1.. Clinical studies have shown that they increase the risk of a heart attack, and of a stroke. Several COX-2 inhibitors have been taken off the market, because of these side-effects. 