TORONTO — Health Canada is alerting Canadians that a class of drugs used for osteoporosis is linked to a slightly higher risk of a rare but serious thigh bone fracture known as an atypical femur fracture.

The advice is the result of Health Canada's review of bisphosphonate drugs, which has led to new warnings and precautions for patients and doctors and will lead to new labels for the drugs.

The department says the risk is higher for those taking the drugs, but the benefits of using the medications to avoid other osteoporosis-related fractures outweighs that risk.

Atypical femur fractures are rare, accounting for less than one per cent of all hip and femur fractures.

They can occur with minimal or no impact to the thigh area, and can occur in both legs in the same person.

Health Canada says patients who are currently taking or who took bisphosphonate drugs previously and who notice new or unusual pain in the hip, groin or thigh should talk to their doctor as this may be a sign of an atypical femur fracture.

The U.S. Food and Drug Administration announced similar findings and warnings in a statement issued in October 2010.

Bisphosphonates are prescription drugs used to treat osteoporosis in men and post-menopausal women. Brand names include Fosamax and Actonel, but there are about 50 generic versions of the drugs listed on the Health Canada statement.

The drugs can also be used to prevent osteoporosis in post-menopausal women and in patients taking glucocorticoids.

Bisphosphonates have long been used in the treatment and prevention of osteoporosis, which is an age-related condition in which painful fractures, disability and deformity can result from loss of bone density.

Health Canada says people prescribed bisphosphonate drugs should not stop taking them unless they are advised to do so by their health-care provider.