FDA Says Abbott Must Seek OK for Synthroid

The Food and Drug Administration has ruled that Abbott Laboratories Inc. must seek approval to keep selling the thyroid drug Synthroid, the No.3 most-prescribed medicine in the U.S., saying it has a “history of problems.”

The ruling raises the prospect that the drug, which millions of Americans take daily, could be pulled from the market, although FDA officials said they would act cautiously and analysts said such drastic action was unlikely.

Abbott said the safety and efficacy of the drug had been “extensively studied and validated” during the 40 years it has been on the market, and the company is working with the FDA to resolve the issue.

Abbott shares fell 36 cents to close at $51.62 on the NYSE.