The Food and Drug Administration says patients taking bisphosphonate drugs like Fosamax appear more likely to suffer the fractures. The agency says it's unclear whether the drugs directly trigger the problem, but it is updating the drugs' labels about the potential risk.
There are currently no guidelines for how long patients should take the drugs, and the FDA says the fractures "may be related to the use of bisphosphonates for longer than five years."
Merck's Fosamax and Roche's Boniva are prescribed to treat osteoporosis, which causes brittle bones and can lead to fractures.
The agency says patients should continue taking the treatments unless directed to stop by their doctor.