(HealthDay) -- The first generic versions of the once-monthly osteoporosis drug Boniva (ibandronate) have been approved by the U.S. Food and Drug Administration.

Osteoporosis, characterized by a thinning of the bones, is the most common type of bone disease, the agency said in a news release Monday. More common in postmenopausal women, it increases the risk of fracture, especially of the hip, spine and wrist.

More than 40 million people in the United States have the disease or are at significant risk for it, the FDA said.

Approvals to produce generic Boniva have been granted to: Apotex Inc., Orchid Healthcare and Mylan Pharmaceuticals. are medically equivalent to the brand-name versions and are subject to the same quality standards, the agency said.

Generic Boniva will be accompanied by a guide that explains potential serious reactions, including esophagus problems; pain in the muscles, bones or joints; low blood-calcium levels; and uncommon thigh-bone fractures.

More common side effects include back pain, indigestion, extremity pain, diarrhea, headache and muscle pain.

Brand name Boniva, produced by Genentech, was approved by the FDA in 2003.

More information: Medline Plus has more about this drug.