NEW YORK (CNN/Money) - The health risks surrounding arthritis painkillers have caused physicians to back away from prescribing Celebrex, rather than propping up sales for the sole remaining cox-2 inhibitor on the market, according to an analyst report.

Prescriptions for Pfizer drug Celebrex have dropped 40 percent since before Sept. 30, 2004, when Merck pulled Vioxx from the market, according to a Wednesday report from Bernstein.

The decline in prescriptions is even more significant considering that Pfizer (down $0.01 to $27.89, Research) withdrew Bextra from the market on April 7, 2005 at the request of the FDA. At that time, the FDA said it was considering a black box, the most serious type of warning, for Celebrex, which has remained on the market. Currently Celebrex does not have black box warning label and Pfizer is in negotiations with the FDA about it.

"Much of Pfizer's guided '06 growth is predicated on demand resurgence for cox-2s, this guidance having been given before Bextra's withdrawal," said the Bernstein report. "Any cox-2 resurgence for Pfizer obviously now must come from Celebrex, which has flattened despite constant physician promotion and the opportunity to capture patients from Vioxx and Bextra withdrawals."

Bernstein analysts project that Celebrex sales in the U.S. will be flat going into 2006.

"We view a Celebrex demand resurgence as unlikely," read the report, authored by Richard Evans and other analysts for Bernstein, which rates Pfizer as a "market-perform," or "hold."

This is bad news for Pfizer, the world's biggest drug maker with $52.5 billion in annual sales, which based its guidance on projections that Celebrex sales would rise, Bernstein said. Pfizer spokeswoman Mariann Caprino would not confirm Bernstein's figures, but said the Celebrex situation would improve once a warning is added to the label.

"Certainly there has been confusion among doctors and patients but this will be clarified by new labeling for all pain relievers that is being negotiated with the FDA at the current time," said Caprino.

The arthritis painkillers work by blocking cox-2, an enzyme that causes inflammation in the joints. The cox-2 drugs have been blamed for increasing the risk of heart attacks and strokes. The FDA allowed Celebrex to stay on the market, but physicians and consumers have not shared the FDA's opinion that Celebrex outweighs its risks because it is more effective than the other cox-2 drugs, according to Bernstein.

A Bernstein survey showed that 50 percent of the arthritis patients who dropped Celebrex said they weren't getting enough pain relief, while 20 percent said they were afraid of risks and 10 percent believed, erroneously, that the drug was recalled.

All three of these cox-2 drugs have been blockbusters. Vioxx sales totaled $2.5 billion in 2003, the last complete year it was on the market. In 2004, Celebrex sales totaled $3.3 billion and Bextra sales totaled $1.3 billion.

Evans does not own Pfizer stock and Bernstein does not do business with the company.

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