I'm a Cox-2 inhibitor, you're a Cox-2 inhibitor, wouldn't you like to be a Cox-2 inhibitor, too? In Pfizer's case, the answer is, "Can we sing a different song?"

On September 30, Motley Fool Income Investor holding Merck (NYSE:MRK) announced it was pulling Vioxx off the shelves because a study suggested the drug increased the risk of heart attack and stroke in patients who have taken it for more than 18 months. The market responded by sending shares down over 40%. Since then, investors have been suffering a few stomach pains over rival Pfizer (NYSE:PFE), slowly bleeding that stock down 12%.

The reason? Guilt by association.

Pfizer makes two drugs called Bextra and Celebrex that, like Vioxx, treat arthritis and other acute pain. Like Vioxx, Bextra and Celebrex also suppress the production of a heart-protecting fat called prostaglandin I2. Therefore, one might conclude that Pfizer's drugs will have the same harmful effects as Vioxx.

But that conclusion has not yet been proven.

In an article in the October 7 New England Journal of Medicine (which I read every night before bed), one expert makes a case for the same harmful effects. Pfizer's president of worldwide development disputes this perspective, stating, "The data we've accumulated over time demonstrate that Celebrex does not increase the risk of serious cardiovascular events in patients with arthritis and pain, even at higher-than-recommended doses." He is backed up by the acting director of the Food and Drug Administration's Center for Drug Evaluation and Research, who pointed out that Vioxx and other Cox-2 inhibitors did not show the same incidence of heart attack and stroke in clinical trials.

Who's right? Who's wrong? Are there hidden agendas? For now, it's impossible to say. But the lesson is that investors should not throw the baby out with the bathwater just because the baby next door is a demon seed. Do you sell Chico's FAS (NYSE:CHS) just because same-store sales at the Gap (NYSE:GAP) went down last month? Not necessarily.

There are four things to do before you panic. Watch. Wait. Research. Act. Until then, take some Cox-2 inhibitor and call me in the morning.

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Fool contributor Lawrence Meyers owns shares of Pfizer and Merck via the Vanguard Health Care Fund, but he does not actually read the Journal of Medicine.