NEW YORK (CNN/Money) - The black box label is the most potent warning in the Food and Drug Administration's arsenal, but it is not necessarily a death knell for drug sales, analysts say.

The label, second only to pulling the drug from the market, can impact sales but it depends on how badly the drug is needed, and this could be good news for Pfizer, analysts say.

The FDA said April 7 it was considering a black box label for Pfizer's blockbuster Celebrex, an arthritis painkiller with $3.3 billion in 2004 sales. On the same day, the agency asked Pfizer (Research) to withdraw its other arthritis drug, Bextra, which had $1.3 billion in 2004 sales. Just six months before, on Sept. 30, Merck (Research) withdrew Vioxx. All three of these drugs are in the same class of cox2 inhibitors and have been blamed for heart attacks and strokes.

"Definitely [Celebrex] sales are going to be impacted by the formalization of the black box," said Sena Lund, analyst for Cathay Financial. "Physicians do not ignore black box warnings because it becomes a matter of liability."

However, Lund said the loss of sales would be tempered by a lack of competition, with Celebrex's status as "the only cox2 in the market."

Andrew McDonald, research analyst for ThinkEquity Partners, said that black box warnings for many drugs "seriously impair drug sales," partly because physicians fear malpractice suits.

"Doctors, when they see a black box warning, it really makes them anxious in that they can imagine themselves, if an adverse event occurs, in a courtroom trying to explain to a judge why they prescribed the medicine when it says right on the label why it shouldn't be prescribed," said McDonald.

But the fear of liability is reduced in situations when the drug is the only treatment available. "If there aren't alternative therapies, then the drug will continue to do well in the marketplace," said McDonald.

The FDA, physicians and patients weigh benefits versus risks when making decisions about drugs, and when a drug offers a unique benefit, it gains an edge.

Cisapride, a treatment for severe nighttime heartburn, was given an black box warning by the FDA in 1995, and an expanded black box warning in 1998, because it was blamed for heart disorders resulting in deaths. Janssen Pharmaceutica withdrew it in 1999 after totaling $1 billion in sales for that year, said McDonald.

"This is a drug that, despite a warning, was still a phenomenal seller," said McDonald, referring to Cisapride.

A similar situation occurred when Remicade, a treatment for rheumatoid arthritis and Crohn's disease, received a black box warning. Remicade, a drug made by Centocor, can cause serious infections, according to the FDA. But McDonald said the drug is still a strong seller, totaling $2 billion in 2004 sales. (See correction.)

"In this case, the sales have not been terribly affected," said McDonald, referring to Remicade. "The needs for the drugs outweigh the risks associated with them. There's a similar story with Celebrex, in that there aren't very good alternatives."

-- An earlier version of the story incorrectly stated that Enbrel, a treatment for rheumatoid arthritis, had also received a black box warning. Enbrel has received warnings from the FDA because of health risks, but not the black box label. CNN/Money regrets the error.