Calcitonin is a hormone your body naturally produces to regulate calcium levels, and a synthetic version (derived from salmon) is used as a medication for three FDA-approved purposes: treating postmenopausal osteoporosis, Paget disease of bone, and dangerously high blood calcium (hypercalcemia). Beyond its role as a drug, calcitonin blood levels also serve as a diagnostic marker for a rare type of thyroid cancer.
How Calcitonin Works in Your Body
Your thyroid gland produces calcitonin naturally. Its main job is keeping calcium levels in your blood from climbing too high. It does this in two ways: it slows down the cells that break down bone (releasing calcium into the blood), and it signals your kidneys to flush out more calcium through urine. The synthetic medication version mimics these same actions, just at higher, controlled doses.
The drug form is made from salmon calcitonin, which is structurally similar to the human version but more potent. It comes as either a nasal spray or an injection, with the nasal spray being the more commonly prescribed form for long-term use.
Postmenopausal Osteoporosis
Calcitonin is approved for treating osteoporosis in women who are at least five years past menopause. It’s not a first-line treatment. Other medications are generally more effective at building bone density, so calcitonin is typically reserved for women who can’t tolerate those alternatives.
The landmark study supporting its use, known as the PROOF trial, followed postmenopausal women with osteoporosis over five years. Those taking a daily 200 IU nasal spray dose, along with calcium and vitamin D supplements, saw a 36% reduction in vertebral fracture risk compared to placebo. The study tested three different doses (100, 200, and 400 IU), and interestingly, the middle dose worked best. The highest dose didn’t provide additional protection. A separate study of daily calcitonin injections found a 31% reduction in hip fracture risk after one year of treatment.
The bone density improvements with calcitonin are real but modest compared to other osteoporosis drugs. Its main practical advantage is that it’s well tolerated and comes as a simple nasal spray, making it an option when stronger medications cause side effects.
Paget Disease of Bone
Paget disease causes bones to break down and rebuild abnormally, leading to enlarged, misshapen, and weakened bones. Treatment aims to slow this chaotic bone turnover and relieve pain. The go-to drugs for Paget disease are bisphosphonates, but some patients can’t tolerate them. Calcitonin serves as a backup option in those cases.
Because calcitonin directly slows the overactive bone-resorbing cells driving Paget disease, it can ease pain, reduce bone turnover, and help normalize blood markers that indicate disease activity. It’s less potent than the preferred treatments, but it fills an important gap for patients with limited options.
Lowering Dangerously High Calcium
When blood calcium spikes to dangerous levels, calcitonin can bring it down quickly. This is its most acute use, typically happening in a hospital setting. Calcitonin injections can be given every six hours for hypercalcemia that hasn’t responded to IV fluids alone.
The advantage here is speed: calcitonin starts working faster than most other calcium-lowering treatments. The downside is that the effect is short-lived, and the body develops tolerance relatively quickly, meaning calcitonin stops working as well after repeated doses. For this reason, it’s usually a bridge treatment, buying time while longer-acting therapies take effect.
Calcitonin as a Cancer Screening Tool
Separate from its role as a medication, calcitonin levels in your blood can flag a rare cancer called medullary thyroid carcinoma. This cancer develops in the C cells of the thyroid, which are the same cells that produce calcitonin. When these cells become cancerous or overgrow (a precancerous condition called C-cell hyperplasia), they often pump out excess calcitonin.
A high calcitonin blood level doesn’t automatically mean cancer. Other conditions, certain medications, and even pregnancy can elevate it. And a normal level doesn’t completely rule out medullary thyroid cancer either, since not all cases produce excess calcitonin. When initial results are uncertain, a stimulation test can provide more clarity. During this test, you receive an IV medication that triggers calcitonin production, and blood samples are drawn at intervals afterward. A sharp rise in calcitonin across those samples raises suspicion for C-cell disease, though additional testing is still needed to confirm a diagnosis.
Side Effects of Calcitonin Medication
The nasal spray is generally well tolerated but comes with predictable nasal side effects. In clinical trials, about 12% of patients experienced runny nose or nasal inflammation, and roughly 11% reported other nasal symptoms like crusting, dryness, irritation, or soreness. Nosebleeds occurred in about 3.5% of users. Outside the nose, the most common complaints were back pain (5%), joint pain (3.8%), and headaches (3.2%).
The injectable form tends to cause more systemic side effects. About 10% of patients getting injections experience nausea, compared to under 2% with the nasal spray. Flushing affects 2% to 5% of injection users but less than 1% of nasal spray users.
The Long-Term Safety Question
In 2013, regulators reviewed whether long-term calcitonin use might increase cancer risk. A meta-analysis of 21 clinical trials found that 4.1% of patients taking calcitonin developed some type of malignancy, compared to 2.9% of those on placebo. The European Medicines Agency pulled calcitonin’s approval for osteoporosis based on this signal. Health Canada did the same.
The FDA took a different position. After reviewing the same data, it concluded there was no conclusive evidence of a causal link between calcitonin and cancer. The agency kept the drug available but updated the labeling to recommend that calcitonin only be used when alternatives aren’t suitable, and that the need for continued treatment should be reassessed periodically. This is why calcitonin remains a second-line option in the United States rather than a first choice for osteoporosis.