Amgen Inc said its experimental bone drug was found to be more effective than an already marketed drug in a late-stage study.

Amgen's drug, romosozumab, met the main goal of showing a significant difference over Eli Lilly & Co's teriparatide in improving total hip bone density by the 12th month in postmenopausal women with osteoporosis.

Osteoporosis is a condition which causes bones to become weak and brittle leading to an increased risk of fracture.

Osteoporosis can occur in both men and women and at any age, but is most common in older women, affecting millions of people in the United States, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

The study tested the safety, tolerability and efficacy of romosozumab in women with postmenopausal osteoporosis that had been previously treated with the commonly used therapy, bisphosphonate.

More than 5 percent of patients on romosozumab experienced adverse events like common cold, join pain, back pain and headache, Amgen said on Tuesday.

Romosozumab is being developed with Belgium's UCB SA.