Updated from 8:26 a.m. EST

There's more pain for drugmakers and new worries for drug users.

The Food and Drug Administration is now warning about heart risks related to the use of naproxen, a long-time popular pain killer sold over the counter, as well as a prescription-strength medication sold under various names.

The latest shock to the industry came Monday night when federal regulators disclosed that the National Institutes of Health last Friday halted a drug study testing whether certain anti-inflammatory drugs could reduce the risk of patients contracting Alzheimer's disease. The drugs were being tested in people 70 years of age or older who were considered to be at increased risk because of family history, but did not have symptoms of the disease.

The study compared Naproxen vs. Celebrex, which is made by Pfizer ( PFE). The best-known over-the-counter version of the drug Naproxen is Aleve.

The Alzheimer's disease test was halted partly because another clinical study involving Celebrex showed that the Pfizer drug increased the risk of cardiovascular problems among patients who took high doses, a development that Pfizer disclosed last Friday and which triggered a selloff in the company's share price. The test, sponsored by the National Cancer Institute, was determining if Celebrex could prevent certain colon polyps that are a precursor to colon cancer.

But this Alzheimer's disease test, called ADAPT, was also halted because it "indicated an apparent increase in cardiovascular and cerebrovascular events" among naproxen patients vs. patients receiving a placebo, the NIH said Monday night.

The test was stopped "as a precautionary measure to ensure the safety of the study's participants," said NIH Director Dr. Elias A. Zerhouni. "The investigators made their decision based on the risk/benefit analysis specific to this trial." The ADAPT trial began in 2001 and was conducted at six U.S. sites. Approximately 2400 volunteer participants were randomly assigned to receive naproxen, Celebrex or a placebo for a time up to three years.

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