They want makers of widely used osteoporosis medicines to clarify how long patients should take them for the greatest benefit and least risk.
The FDA itself will decide later what the new labels should say for each of the drugs: Fosamax, Boniva, Actonel, Atelvia and Reclast.
A few patients have suffered serious complications, including jawbone destruction and unusual thighbone fractures, generally after several years of taking the medicines.
The drugs stop and reverse dangerous thinning of bones in many people, preventing much more common hip and spine fractures that cause pain and can result in hospitalizations, nursing home stays and early death.
But after several years, it's unclear whether the drugs, a class called bisphosphonates, do more harm than good.
More than 10 million Americans, mostly women over age 50, have osteoporosis, and 34 million more have low bone mass that could lead to osteoporosis, in which the body breaks down bone tissue faster than it rebuilds it.
The Associated Press contributed to this report.
