Several recent studies show that aspirin, Indocin, Celebrex and other arthritis pain medicines may cause some cases of hyponatremia. These medications, often taken to relieve muscle and joint pain, can cause the body to retain fluid during exercise (Medicine & Science in Sports & Exercise, May 2005).
For more than 40 years, sports medicine experts have told athletes in endurance events to take fluids frequently during events lasting more than one hour. However, on rare occasions, novice athletes have died of hyponatremia in these endurance events. Hyponatremia is caused by drinking too much fluid and is not caused by excessive loss of salt in sweat. The extra fluid expands blood volume and dilutes blood salt levels, which forces fluid to enter and swell the brain, causing nausea and vomiting, weakness, headache, and extreme tiredness. Since these same symptoms can be caused by dehydration alone, the only way to diagnose hyponatremia is with blood tests.
How much fluid should you drink? Experts do not agree because thirst is a late sign of dehydration. The American College of Sports Medicine recommends three to six cups of fluid per hour. For a person who is not exercising near his maximum, this could be too much. The person who is exhausted and exercising significantly below his capacity probably should take in only two to three cups per hour. Above all, do not take aspirin or any arthritis pain medicines before you compete in events taking more than an hour.