Calcitonin is a polypeptide hormone secreted by the parafollicular cells of the thyroid gland in mammals and studied in late 1970s postmenopausal osteoporosis treatment. The primary pharmacological effect of porcine calcitonin is its activity at specific osteoclast receptors, resulting in diminished osteoclast activity at extremely low concentrations and leading to the normalization of bone resorption and the formation and maintenance of functional bone. It also promotes the mineralization of bone, as acute studies in rats, rabbits and young pigs have shown, as well as exerting a regulatory effect on renal electrolyte excretion. The overall result is that bone mass is maintained or increased, with no adverse effect on cortical bone. In clinical trials porcine Calcitonin significantly increased the bone mineral density of the lumbar spine compared with placebo, but unfortunately did not influence the risk of new vertebral fractures.