The calcium-sensing receptor (CaSR) belongs to the family C G-protein coupled receptors (GPCRs). CaSR is expressed in the parathyroid gland, where it regulates the release of parathyroid hormone, maintaining calcium homeostasis. CaSR antagonists have undergone clinical trials to test their validity as an osteoporosis treatment, with suboptimal results. Research is currently being done on the potential of CaSR antagonists as treatments for asthma and Alzheimer’s. Allosteric modifiers to CaSR, such as the drugs cinacalcet and etelcalcetide, are used to treat hyperthyroidism by decreasing the release of parathyroid hormone.