Some of the Celebrex’s detractors contend that its risks are still not fully understood, and argue that Pfizer is dragging its feet on a study — now nearly six years old — evaluating the drug’s heart risks. The study is scheduled to end in May 2014, the same month that Celebrex loses its patent protection and sales of the drug are expected to plunge.

Then and now, Pfizer has defended its decision to release partial results from the 2000 study and denies any intent to deceive. Company officials have said the drug has demonstrated its worth and safety. The proof, they say, is that 33 million Americans have taken it. “The bottom line is Celebrex is a very important option for many of these patients,” said Dr. Steve Romano, head of the medicines development group in Pfizer’s primary care unit.

The decision by Pfizer and Pharmacia to withhold crucial data became widely known in 2001, after the Food and Drug Administration released the study’s full results. The revelations, along with similar reports of withheld data by other drug companies, led to calls for reforms in the way data from clinical trials is published, including in The Journal of the American Medical Association, which ran an article featuring the partial results from the study.

The withheld data also led to a lawsuit, filed in 2003, by several pension funds that charged that by handling the results the way they did, Pfizer and Pharmacia had misled investors and were responsible for a drop in Pharmacia’s stock value when the full results were revealed.

Lawyers for Pfizer and for the pension funds declined to comment. In a statement, company officials said they were confident they would prevail when all the evidence was heard. “The few documents handpicked by lawyers suing Pfizer and being reported by The New York Times are not a fair representation of this body of evidence,” the company said.

The documents show that in February 2000, Pharmacia employees came up with a game plan on how they might present the findings once they were available.