Parathyroid Hormone (Natpara): What It Is and How It Works

At a glance

What is parathyroid hormone?

The parathyroid hormone product Natpara is a recombinant copy of the full 84-amino-acid human hormone, rhPTH(1-84), that the parathyroid glands normally release to keep blood calcium in a healthy range. In hypoparathyroidism, those glands are missing or underactive, and patients must rely on large doses of calcium and active vitamin D that are hard to balance. Natpara replaces the hormone itself. It was approved in the United States in 2015.

How does parathyroid hormone work?

Parathyroid hormone binds the PTH-1 receptor and raises blood calcium through several routes:

• It increases calcium reabsorption in the kidney.
• It stimulates the kidney to activate vitamin D, which boosts calcium absorption from the gut.
• It mobilizes calcium from bone.

Replacing the hormone in hypoparathyroidism restores this physiologic control, which calcium and vitamin D supplements alone cannot fully reproduce. The clinical goal is to maintain normal calcium while reducing the heavy supplement burden these patients otherwise carry. In the REPLACE trial, a majority of patients on rhPTH(1-84) achieved at least a 50 percent reduction in their calcium and active vitamin D doses while keeping blood calcium stable, compared with almost none on placebo.

Is it FDA-approved?

Yes. Parathyroid hormone (Natpara) was approved by the FDA in 2015 for hypoparathyroidism. It carries a boxed warning about osteosarcoma seen in rats and is available only through a restricted program. Its U.S. availability has been limited following a 2019 recall over a manufacturing issue and the manufacturer's decision to discontinue the product; the newer long-acting agent palopegteriparatide (Yorvipath) has since been approved for the same condition.

What is parathyroid hormone prescribed for?

Natpara is used as an add-on to calcium and active vitamin D to control low blood calcium in people with hypoparathyroidism who are not well managed on supplements alone. Because of its restricted program and limited supply, treatment decisions are individualized with a specialist.

What are the side effects?

Common side effects include:

• Tingling sensations (paresthesia)
• High or low blood calcium
• Headache and nausea
• Increased calcium in the urine More serious considerations include:
• A boxed warning about osteosarcoma based on rat studies, which is why it is used under a restricted program
• Swings in calcium when doses are started, changed, or interrupted

Evidence strength

FDA approved: Parathyroid hormone (Natpara) is FDA-approved for hypoparathyroidism, supported by the REPLACE trial showing reduced supplement needs while maintaining calcium.

Sources: FDA prescribing information for Natpara; Mannstadt et al. (2013), the REPLACE trial. PubMed-indexed studies are cited by DOI where used. This article is for educational purposes only and is not medical advice.