Pfizer Inc. on Monday said the label of its Celebrex arthritis drug has been changed to add a prominent warning of possible cardiovascular risks, such as an increased chance of heart attacks, in line with new warnings on other arthritis and pain drugs.

The label will also carry a new warning that Celebrex, like older painkillers, can cause serious ulcers and gastrointestinal bleeding.

Celebrex was developed to treat pain with less risk of such bleeding than older treatments. But in a large clinical trial, Celebrex failed to prove significantly safer for the stomach than two far-cheaper standard painkillers.

Pfizer said the package insert label of the drug now recommends it be prescribed "at the lowest effective dose for the shortest duration."

The label will now also note that Celebrex more than doubled the risk of heart attack in a 3-year cancer-prevention trial sponsored by the federal government, although it did not show such danger in a similar cancer-prevention study.