Advertisements for the arthritis drug Celebrex (search) were misleading and unsubstantiated, overstating the pain reliever's benefits and understating the risks, the government said Wednesday.

The Food and Drug Administration asked for an immediate halt to all ads for Celebrex, which Pfizer Inc. (search) did last month in advance of the agency's letter. A study in December found high doses of Celebrex were associated with an increased risk of heart attack.

The letter, sent Monday and released Wednesday, details the misleading and unsubstantiated claims in ads for Celebrex and a related drug, Bextra, that appeared on television, in print, on TV infomercials and in direct-mail brochures. The government said the claims represent serious violations of federal law.

New York-based Pfizer spent more than $70 million advertising best-selling Celebrex to U.S. consumers in the first nine months of last year. It has run minimal consumer ads promoting Bextra.

When Pfizer voluntarily pulled its ads in December, the company said it planned to keep Celebrex on the market and would continue marketing the drug to doctors.

Vioxx (search), a drug in the same class as Celebrex, has been found to be associated with higher rates of heart problems and stroke. Its manufacturer, Merck & Co., pulled the pain killer off the market last fall.

The FDA has said it is considering warning labels for Celebrex or ordering its withdrawal from the U.S. market altogether.

Before the recent studies detailing their side effects, anti-inflammatory drugs such as Celebrex and Vioxx were heavily promoted by the pharmaceutical industry as being more effective and less irritating to the stomach than some other pain relievers.

But five ads for Celebrex and/or Bextra (search) reviewed by the FDA were found to be misleading and in violation of federal law, the agency said. They omitted facts, including information about risks, wrongly claimed superiority and made unsubstantiated claims about the drugs' effectiveness, the FDA said.

The FDA asked the company to detail any ads that make similar misleading claims and keep them off the air as well.

Among those cited in the letter:

—"Guitar" TV ad: This is a "reminder ad," which is supposed to call attention to the name of a drug without giving any details — including what it is meant to treat or what the risks are. In this case, the ad showed a woman playing guitar, focusing on her hands and fingers while a voice says, "With Celebrex, I play the long version."

The FDA said this suggested the woman had better movement and flexibility and was therefore able to play the longer version of the song where she previously could not — making a claim about Celebrex's benefits without explaining any side effects.

—"Arthritis tips" TV ad: The ad opens with, "Celebrex presents, arthritis tips," and goes on to give facts about the disease. Celebrex is mentioned again at the end of the ad, which clearly suggests that the drug is the arthritis treatment, the FDA said. It said the ad suggests that Celebrex is effective in treating problems such as "crippling disability" when it will simply relieve the signs and symptoms, not modify the disease itself. Overall, the agency said, the ad "greatly overstates the proven benefits of Celebrex."

—An infomercial called "On the Road to Joint Pain Relief": The 27-minute show includes testimonials and statements from health care providers promising dramatic effects and complete pain-free relief. It repeatedly mentions Pfizer and points consumers to the company for more information, yet the ad omits information about the drug's safety and risks.

Pfizer spokeswoman Mariann Caprino said the company had received the letter but had no other comment.

Sales of Celebrex and Bextra had been expected to total more than $4 billion worldwide in 2004, nearly 10 percent of Pfizer's revenue.