Cleveland Clinic researchers are reporting that two popular arthritis drugs may cause blood clots, heart attacks, and strokes. The researchers analyzed several studies in which at least 18,000 people took the cox-2 inhibiting drugs Vioxx or Celebrex for pain relief. In patients taking the medications, researchers found a marked increase in blood clotting leading to cardiovascular problems. The results of the study are published in the Journal of the American Medical Association.

Cox-2 inhibitors are popular because they cause less gastrointestinal side effects than conventional pain relievers such as aspirin. Both Merck, the maker of Vioxx, and Pharmacia, the manufacturer of Celebrex, dispute the study's conclusions.

One of the study's authors suggested that doctors investigate their patients' cardiovascular histories before prescribing any cox-2 inhibitor. Although more research needs to be conducted in the area, the authors believe the study indicates a startling trend.

Earlier this year, a University of Pennsylvania research team published the results of an unrelated study of cox-2 inhibitors. The Pennsylvania researchers found that while the inhibitors effectively block the pain producing cox-2 enzyme, the medications also inhibit the production of prostacyclin, a substance vital in dissipating blood clots.