Washington ? A study testing whether Celebrex or naproxen would reduce the risk of Alzheimer’s disease was halted Monday after researchers noted an increase in heart attack and stroke among participants who were taking naproxen, an over-the-counter pain reliever on the market for nearly 30 years.

Officials at the National Institutes of Health said the study was stopped after three years when it was noticed that patients taking naproxen, sold under the brand name Aleve, had a 50 percent greater incidence of cardiovascular events — heart attack or stroke — than patients taking placebo.

Another factor, officials said, was the announcement last week that advertising for Celebrex was being halted after a study found that high doses of the drug were associated with an increase in heart attack risk. Data from the Alzheimer’s study, however, did not indicate an increased risk for heart attack or stroke.

Celebrex and naproxen are both pain relievers commonly used to treat arthritis. Naproxen has been approved for sale, first as a prescription and then as an over-the-counter drug, since 1976.