A 10-pounds-a-day jab can repair damaged joints and could benefit millions crippled by osteoarthritis, researchers at New York's University of Rochester Medical Centre have suggested.
The powerful drug is said to thicken cartilage by 37 percent, greatly protecting joints from degeneration, the Daily Express reported.
The medication, called Forsteo, or teriparatide, is made from a potent bone and joint-mending hormone.
It has been in use in the UK for eight years to build bone mass in those at risk of fracture, for example in patients suffering from the brittle bone disease osteoporosis.
The jab works by increasing the action of the bone formation cells - osteoblasts - that speeds up bone formation, keeping bones strong.
But US researchers discovered the injection can also help build up the cartilage around joints, meaning it could be "reprogrammed" to treat arthritis.
The researchers noticed that occasionally, when a patient suffered from both osteoporosis and osteoarthritis, the symptoms of arthritis would improve after taking Forsteo for osteoporosis.
This group reported less pain and a higher ability to function than a matched population of patients who were not taking the drug.
Dr Michael Zuscik, who co-authored the study, admitted that more studies were needed before its use could be extended to treat osteoarthritis as there have been concerns about the safety of Forsteo, which is made by the pharmaceutical giant Lilly.
His team's findings have been published in the journal Science Translational Medicine.