Pfizer Inc.‘s pain drug Celebrex has a “probable increased risk” of heart attacks in higher doses but “no apparent effect” in 200 milligram doses or less, a veteran U.S. Food and Drug Administration scientist said on Thursday in a written presentation.

David Graham, associate director for science and medicine at the agency’s Office of Drug Safety, said preliminary data from an unpublished study also showed Pfizer’s other pain reliever, Bextra, did not show a heart attack risk in doses of 20 milligrams or less.

Graham is regarded as a maverick for his forthright criticism of the FDA’s ability to monitor the safety of drugs once they are on the market. He will present the findings Thursday morning from a study he says is larger than any previous related study.

His presentation will help kick off the second day of an unusual three-day meeting called by the FDA after Merck withdrew its popular arthritis drug Vioxx in September when a study showed it caused increased risk of heart attack and stroke.

Vioxx, Celebrex and Bextra are all part of a class of drugs known as COX-2 inhibitors, which were designed to ease pain as effectively as older, nonprescription drugs known as nonsteroidal anti-inflammatory drugs, or NSAIDs, while being easier on the stomach.

The FDA is asking two outside advisory committees if the group of medicines offer enough benefits to stay on the market, if they need stronger warnings, and if further research is needed.

Graham’s study analyzed data culled from California’s Medicaid health insurance program for the poor, called Medi-Cal, for more than 15,000 heart attack patients.

The study also concluded Vioxx had a “definite” increased risk of heart attacks in patients who took doses higher than 25 milligrams. The risk “begins early in therapy, and is apparent during days 1-30 of use,” Graham’s presentation said.