FDA-approved
Hormones & metabolism
Pegvisomant
Pegvisomant (Somavert) is an FDA-approved growth hormone receptor blocker for acromegaly. Learn how it lowers IGF-1, how it is given, and the research.
- Reviewed by
- William Maish, MD MBA MPH, Clinical Product Lead
- Published
- October 5, 2026
- Last updated
- October 5, 2026
Key takeaway
Pegvisomant (sold as Somavert) is a modified, pegylated version of growth hormone that works as a growth hormone receptor blocker, used to treat acromegaly when other therapies fall short. Rather than suppressing the pituitary, it stops growth hormone from acting at its receptor, which normalizes insulin-like growth factor 1 in the large majority of patients. It has been FDA-approved in the U.S. since 2003 and is given as a daily subcutaneous injection.
At a glance
| What it is | A pegylated growth hormone receptor antagonist |
| Approved for | Acromegaly inadequately controlled by other treatments |
| Key fact | In a controlled trial, daily dosing normalized IGF-1 in roughly 90% of patients at the higher dose |
| Route | Subcutaneous injection, once daily |
| Evidence strength | FDA approved |
What is pegvisomant?
Pegvisomant, sold under the brand Somavert, is a genetically engineered analog of human growth hormone that has been chemically altered and attached to polyethylene glycol (PEG). Unlike the somatostatin analogs that lower growth hormone output from the pituitary, pegvisomant acts at the target: it blocks growth hormone from signaling at its receptor. It was developed from a mutated growth hormone molecule known as B2036 and approved in the United States in 2003.
How does pegvisomant work?
Pegvisomant binds the growth hormone receptor but, because of its engineered substitutions, prevents the receptor from changing shape in the way needed to transmit a signal. Growth hormone normally works by bringing two receptor subunits together; pegvisomant occupies the receptor and blocks that functional pairing, so the downstream production of insulin-like growth factor 1 (IGF-1) in the liver falls. Because the disease activity in acromegaly tracks with IGF-1, lowering it improves symptoms.
A distinctive feature is that pegvisomant works peripherally at the receptor and does not reduce the pituitary tumor's growth hormone output, so measured growth hormone levels actually rise even as IGF-1 normalizes. The PEG attachment extends its half-life to allow once-daily dosing. In a controlled trial, pegvisomant normalized IGF-1 in about 90 percent1 of patients at the 20 mg daily dose, with symptom improvement.
Is it FDA-approved?
Yes. Pegvisomant was approved2 by the FDA in 2003 for acromegaly. It is given as a daily subcutaneous injection, usually starting with a loading dose and then a daily maintenance dose titrated to IGF-1 levels.
What is pegvisomant prescribed for?
Pegvisomant is prescribed for acromegaly in people who have not responded adequately to surgery, radiation, or other medical therapy, or for whom those options are not appropriate. Because it lowers IGF-1 without shrinking the tumor, patients are monitored with periodic pituitary imaging.
What are the side effects?
According to the prescribing information, common side effects include:
- Injection-site reactions, including fatty lumps (lipohypertrophy)
- Infections, such as cold symptoms
- Pain
- Nausea and diarrhea
- Flu-like symptoms
- Abnormal liver tests
More serious considerations include:
- Elevated liver enzymes and, rarely, liver injury, so liver tests are monitored
- Low blood sugar in people with diabetes, whose medications may need adjustment
- The need to monitor tumor size over time
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Sources: FDA prescribing information for Somavert; the controlled pegvisomant trial (Trainer et al., New England Journal of Medicine, 2000, DOI: 10.1056/NEJM2000042034216041), indexed on PubMed. This document is educational and does not constitute medical advice.