Arthritis causes pain, stiffness, and swelling in the joints. There are many types of arthritis, but the most common types are osteoarthritis and rheumatoid arthritis. Osteoarthritis results from wear and tear on the joints. Rheumatoid arthritis is a condition of the immune system that damages the joints. Pain is a problem in both of these types of arthritis. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, are common treatments for arthritis pain. Unfortunately, NSAIDs can irritate the stomach and cause ulcers, which are open sores in the stomach lining. In addition to being painful, ulcers can bleed, sometimes severely. Cyclooxygenase-2 (COX-2) inhibitors are other drugs that treat arthritis pain. Examples of COX-2 inhibitors are celecoxib and rofecoxib. COX-2 inhibitors are as effective as NSAIDs but irritate the stomach less. COX-2 inhibitors are much more expensive than NSAIDs. Since most people receiving NSAIDs never develop ulcers, it is unclear whether the increased costs of COX-2 inhibitors are worth the potential benefits.