Vioxx is a non-steroidal anti-inflammatory drug (NSAID) that contains the active ingredient rofecoxib. The drug has been most commonly prescribed to treat osteoarthritis, rheumatoid arthritis, pain, and migraines. The mechanism of action of Vioxx involves the inhibition of the enzyme cyclooxygenase-2 (COX-2), which effectively impedes the synthesis of prostaglandins, the hormone-like substances that cause pain and swelling. Vioxx and other COX-2 inhibiting drugs are associated with fewer gastrointestinal side effects, such as ulcers, than traditional NSAIDs because the newer medications are selective and do not affect COX-1, another form of the cyclooxygenase enzyme that is important in producing the protective gastric mucosa lining the gut. In 2004, however, the maker of Vioxx, Merck and Company, Inc., voluntarily withdrew the drug from the market due to evidence that its long-term use can cause an increased risk of heart attacks, strokes, and other cardiovascular events.