(NaturalNews) A growing body of evidence suggests that a popular family of osteoporosis drugs may actually lead the weakening of bones, increasing the risk of fractures.

Use of bisphosphonates such as Merck's Fosamax for more than five years may predispose women to break their femurs (thigh bones), yet neither Merck nor the FDA has made any effort to warn doctors of this fact.

"We are seeing [thigh fractures in] people just walking, walking down the steps, patients who are doing low-energy exercise," said Dr. Kenneth Egol of New York University.

The injuries in these patients appear more similar to those that would be expected from a car accident than from a minor fall, he said. Noting that "the femur is one of the strongest bones in the body," Egol called the pattern "very unusual."

"Over the last 18 months we are seeing this more frequently," he said.

Fosamax, sold generically as alendronate, has become a best-seller, with doctors now prescribing it even to women who are considered "at risk" of osteoporosis. Yet even before the risk of femoral fractures emerged, the drug had already been linked to severe musculoskeletal pain and a jaw disease known as osteonecrosis.

In 2008, the FDA first contacted Merck about the emerging evidence regarding thigh fractures. Sixteen months later, Merck added the fractures to a list of potential side effects without further comment

"It took Merck an entire year to respond," said Richard Besser, senior health and medical editor for ABC News. "Just six words: 'low energy femoral shaft and subtrochanteric fractures.'"

Because Fosamax is designed to interfere with the body's natural bone-maintenance mechanisms, researchers believe that over the long term, it undermines the skeleton's ability to regenerate.

"When they are on it for five, six, seven or eight years, they lost their ability to remodel and regenerate their skeleton," said orthopedic trauma surgeon Joseph Lane of the Hospital for Special Surgery in New York City. "[Some women] are very vulnerable and they will then develop problems of brittle bone."

Sources for this story include: http://abcnews.go.com/GMA/OnCall/fosamax-lon....