Pegvisomant
Growth Hormone Receptor AntagonistapprovedAlso known as: Somavert, B2036-PEG
A PEGylated growth hormone receptor antagonist that blocks GH action at the receptor level, used to treat acromegaly by normalizing IGF-1 levels without reducing GH secretion.
Overview
Pegvisomant (brand name Somavert) is a genetically engineered analog of human growth hormone that has been structurally modified to act as a GH receptor antagonist. It contains 9 amino acid substitutions and is conjugated with polyethylene glycol (PEG) polymers to extend its half-life. Unlike somatostatin analogs that reduce GH secretion, pegvisomant works by blocking GH from binding to its receptor, preventing downstream IGF-1 production. It is the most effective therapy for normalizing IGF-1 levels in acromegaly, achieving normalization in up to 97% of patients. It received FDA approval in 2003 and represents a unique approach as the only GH receptor antagonist approved for clinical use.
Mechanism of Action
Pegvisomant antagonizes the GH receptor through multiple mechanisms: (1) Binds to the GH receptor at Site 1 with high affinity but prevents functional receptor dimerization due to amino acid substitutions at Site 2; (2) Blocks GH-induced JAK2/STAT signaling cascade; (3) Reduces hepatic IGF-1 production, lowering circulating IGF-1 levels; (4) PEGylation extends half-life to ~6 days by reducing renal clearance and proteolytic degradation; (5) Does not affect GH secretion from the pituitary — GH levels actually rise due to loss of IGF-1 negative feedback.
Molecular Formula
Protein (~22 kDa core + PEG)
Molecular Weight
~42,000 g/mol (with PEG chains)
Sequence
191 amino acid modified GH analog with 9 point mutations (PEGylated)
Dosage Protocols
Dose Range
10mg – 30mg
Frequency
Once daily
Route
subcutaneous
Cycle Length
Ongoing
Loading dose of 40mg SC, then 10mg daily. Titrate based on IGF-1 levels every 4-6 weeks. Maximum dose 30mg/day. Monitor liver function.
Source: FDA prescribing information (Somavert)
🧮 Personalized Dosage Calculator
💰 Estimated Pricing
Typical Supply
10-30mg daily injection vials
Last Updated
2026-02
Brand Somavert. GH receptor antagonist for acromegaly. Very expensive. ~$5,000-8,000/mo. Insurance/specialty pharmacy essential.
⚠️ Prices are estimates based on publicly available data and may vary significantly by vendor, location, and prescription status. This is not medical or financial advice.
Side Effects
| Effect | Severity |
|---|---|
| Injection site reactions | mild |
| Elevated liver enzymes | moderate |
| Headache | mild |
| Pituitary tumor growth | severe |
| Flu-like symptoms | mild |
Pros & Cons
Most effective therapy for normalizing IGF-1 in acromegaly (up to 97% normalization rate)
Unique mechanism — works even when somatostatin analogs fail to control disease
Can be used in combination with somatostatin analogs for refractory cases
Improves insulin sensitivity and glucose metabolism unlike somatostatin analogs
Requires daily injections (no long-acting formulation available)
Very expensive — costs $50,000-100,000+ per year
Requires regular liver function monitoring due to hepatotoxicity risk
May allow pituitary tumor growth due to loss of IGF-1 negative feedback
Research Studies
🩸 Blood Work
No specific bloodwork requirements reported for this peptide. General health panels are always recommended before starting any peptide protocol.
Legal Status
FDA-approved as Somavert for acromegaly (2003). Prescription-only medication. Available as subcutaneous injection. Not a controlled substance.
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