Calcitonin

Calcitonin treats osteoporosis by binding to the tissue osteoclasts and inhibit mineral resorption to the bloodstream. is a peptide composed of 32 amino acids which binds to osteoclasts and inhibits bone resorption. It is a protein (actually a polypeptide) and is produced in the thyroid. The body uses it as part of a homeostatic system in opposition to parathyroid hormone.

As a drug, the calcitonin can be taken from other animals - salmon calcitonin is the one most widely used. It is highly potent in humans because of its high affinity (forty times that of human calcitonin) for the human calcitonin receptor and its slow rate of clearance. Human calcitonin is sometimes used. The FDA has approved calcitonin for administration by the subcutaneous, intramuscular, and intranasal routes. The bioavailability of nasal calcitonin is only about 25 percent that of intramuscular calcitonin.

Calcitonin can be used for treatment of high calcium levels (hypercalcaemia) and osteopenia. It is also effective in treatment of established osteoporosis, but it used less often than other drugs. Calcitonin is less effective for the treatment of postmenopausal osteoporosis than bisphosphonates

There are conflicting data on the effect of calcitonin on sites other than the spine. Two studies found that calcitonin had no beneficial effect outside the spine, but other studies have shown improvement

Calcitonin can relive pain in patients who have sustained a fracture, although experts don't understand the mechanism behind the pain mitigation. Some doctors give calcitonin to osteoporosis patients if pain is a problem, and then switch to other methods such as bisphosphonates once the pain has gone down.

An early theory held that a deficiency in the body’s natural calcitonin contributed to osteoporosis but that turned out not to be true. Mice bread to remove the calcitonin gene actually have higher bone density than normal mice.