Meece E replied: "Ibuprofen, like other non-steroidal anti-inflammatory drugs (NSAIDs), has several potential side effects. The two most frequently affected organ systems are the renal (kidneys) and gastrointestinal (GI) systems. In the case of the former, kidney damage, usually reversible, can result from chronic ingestion of NSAIDs. It may also happen as the result of short term ingestion, (i.e. one or two doses). There are contributing factors which increase the risk of renal toxicity (e.g. diabetes, dehydration). Apart from damage to the kidneys, NSAIDs alter how the kidneys regulate sodium and water balance -- which may have profound consequences in hot training and racing environments. The GI system is also a site for potential damage from NSAIDs. Stomach ulcers can be a potentially serious consequence of NSAID use, particularly if the ulcers bleed. NSAIDs have also been shown to cause gastritis, and irritation elsewhere in the GI tract (e.g. diarrhea). NSAIDs also inhibit platelet function and thus contribute to bleeding. This may make injuries worse (e.g. more bleeding into a torn muscle). Finally, NSAIDs alter the function of neutrophils (one type of white blood cell). This may impair response to infectious agents -- viruses and bacteria. I strongly recommend against the routine use of NSAIDs during training and racing. They will not make you faster, nor help you recover quicker. The use of these medications during very challenging conditions, such as an Ironman, is particularly dangerous. You may as well wear a sign, "Please kill my kidneys". NSAIDs are useful for short term treatment of overuse injuries, but it is a mistake for the athlete to rely on this treatment long term. The athlete is much better off examining the conditions that lead to the injury -- both biomechanical and training schedule. If these issues are not addressed, then the injury will keep recurring. As always, if you are being treated for any illness, or injury, ask your doctor. "