The US Food and Drug Administration (FDA) has warned patients that a class of drugs widely used to treat women with osteoporosis might be associated with a serious type of thigh bone fracture.

The watchdog has reported cases of atypical femur fractures in patients taking bisphosphonates for longer than five years.

The FDA has stressed that it isn’t clear if bisphosphonates were the cause of the fractures or if there’s an optimal duration of use for the drugs.

The agency will amend all drug labels and provide a medication guide that outlines the risks and benefits of the products.

W omen currently prescribed the drugs shouldn’t stop taking them without speaking to their doctor, it added.