Three generic drugmakers may now sell their own versions of the bone-loss drug Boniva, the FDA ruled today.

Boniva, known by the generic name ibandronate, is a once-a-month pill prescribed to prevent or to treat bone loss from osteoporosis.

The FDA officially approves Boniva only for treatment of postmenopausal women, as the clinical studies that led to approval mostly enrolled women. However, doctors often prescribe the drug to men.

Overall, some 40 million Americans either suffer osteoporosis or are at high risk of the condition, which can lead to devastating bone fractures.

"Men as well as women are affected by osteoporosis, a disease that can be prevented and treated," Keith Webber, PhD, an FDA deputy director, says in a news release.

Boniva is a member of a class of drugs called bisphosphonates, which help build bone.

Webber said the newly approved generic versions of Boniva should make the medication more affordable.

Generic ibandronate will be made by three firms: Apotex Inc., Orchid Healthcare, and Mylan Pharmaceuticals Inc. They will make 150 milligram ibandronate tablets.

The FDA will require each firm to give patients a medication guide describing the drug's risks. Ibandronate can cause serious side effects including esophagus problems; low calcium levels in the blood; bone, joint, or muscle pain; severe jawbone problems; and unusual thigh bone fractures.

In clinical trials for Boniva, the most commonly observed adverse reactions were back pain, indigestion, pain in the arms or legs, diarrhea, headache, and muscle pain.