A new U.S. Food and Drug Administration analysis raises questions about long-term effectiveness among women of the widely prescribed osteoporosis drugs known as bisphosphonates.

The safety of the bone-building drugs, which include brands such as Boniva and Reclast, has been a topic of debate. The FDA’s analysis found that after three to five years of use, bisphosphonates offer little to no benefit.

FDA reviewers said it’s possible long-term use of the drugs could actually weaken bones, leading to adverse events such as femur fractures and esophageal cancer.