Pegvisomant
A growth hormone blocker for acromegaly that acts where the hormone lands, not where it is made
Pegvisomant blocks the growth hormone receptor, so the excess hormone a pituitary tumour produces can no longer drive IGF-1 up. Approved in 2003 for acromegaly when surgery or radiation has not been enough, it is injected daily and dosed by IGF-1 alone.
What is it?
In acromegaly a pituitary tumour secretes too much growth hormone, and the liver answers with too much IGF-1, which drives the overgrowth of hands, face and organs. Most treatments try to cut the hormone's secretion. Pegvisomant does something different: it occupies the growth hormone receptor without activating it, so IGF-1 falls while growth hormone itself goes on circulating.
That difference sets the dosing rules: the label titrates by IGF-1 alone, in 5 mg steps between 10 and 30 mg a day after a 40 mg loading dose, and warns against adjusting by growth hormone levels or symptoms, because the drug cross-reacts with growth hormone assays.
The trial and the clinic tell somewhat different stories. In the 12-week pivotal trial, 89% of patients on 20 mg a day normalised IGF-1. In ACROSTUDY, which has followed more than 2,000 patients in routine care, 53% were normal at one year and 73% at ten, as average doses rose from 12.8 to 18.9 mg. Its final report on 1,464 patients treated with pegvisomant alone for a median of six years put the figure at 62% at last observation. One centre, using it alone or with somatostatin analogues, reported full control in 91% at ten years.
Control matters because IGF-1 tracks survival. In ACROSTUDY, higher IGF-1 on treatment went with more deaths from heart, cancer and lung causes. Because the drug blocks the hormone's effect rather than the tumour, the registry kept imaging it: 7.2% of those scanned showed tumour growth, and most did not change.
It is also used on top of somatostatin analogues when those fail alone; across nine studies the combination normalised IGF-1 in 66%. The label's warnings are about the liver, with baseline tests and closer monitoring if enzymes rise, and about blood sugar: insulin sensitivity improves as growth hormone is blocked, so people with diabetes may need less medication.
Mechanism of Action
Pegvisomant is a modified growth hormone, with polyethylene glycol attached, that binds the growth hormone receptor without switching it on (label).
Receptor blockade
Binds growth hormone receptors on cell surfaces and blocks the body's own growth hormone from signalling (label).
IGF-1 falls
Blocking the receptor lowers IGF-1 and other growth hormone-dependent proteins such as IGFBP-3; growth hormone levels themselves are not the target.
Slow and long
PEGylation slows clearance: levels peak 33 to 77 hours after injection and the half-life is 60 to 138 hours (label).
Published Research
These are the studies in people, read from their PubMed abstracts, with dosing from the Somavert label read October 1, 2026.
The pivotal trial
In a 12-week randomized, double-blind trial in 112 people with acromegaly, IGF-I fell by 27%, 50% and 63% on 10, 15 and 20 mg a day (4% on placebo) and became normal in 54%, 81% and 89% (10% on placebo). Ring size, soft-tissue swelling, sweating and fatigue improved on the two higher doses, and adverse effects were similar across groups.
Twelve years in routine care
The second interim analysis of ACROSTUDY, 2,090 patients, found IGF-I normal in 53% at year one and 73% at year ten as the average daily dose rose from 12.8 to 18.9 mg. On local MRI, 72% showed no change in tumour size, 17% a decrease and 7% an increase; 3% of those with normal liver tests at the start developed ALT or AST above three times normal.
ACROSTUDY final data: 1,464 patients
On pegvisomant alone for a median of 6 years, 62.3% had normal IGF-I at last observation on a median 15 mg a day; 7.2% of those imaged had tumour growth, and none of the 31 deaths was judged treatment-related.
What predicts death on treatment
In 2,077 ACROSTUDY patients followed for a median 4.1 years, higher on-treatment IGF-I was linked to more cardiovascular, cancer and respiratory deaths (hazard ratio 1.97 for cardiovascular causes).
Ten years at one centre
Of 45 patients treated for at least five years, alone or with somatostatin analogues, 91% had full disease control at ten years; liver enzymes stayed stable and no lipohypertrophy was recorded.
Bone quality on long-term treatment
In 25 patients, spine density improved but hip density fell in men over about seven years, and after about nine years bone microarchitecture was poorer than in healthy controls and similar to other treated acromegaly patients.
Insulin resistance without acromegaly
In four insulin-resistant men without acromegaly, 20 mg a day for four weeks halved IGF-1 but did not change insulin sensitivity, glucose output or fat breakdown.
What it does to blood sugar
A meta-analysis of 18 prospective studies, 550 people, found fasting glucose, HbA1c, fasting insulin and insulin resistance all fell on pegvisomant, independently of IGF-1 control; added to a somatostatin analogue, it offset that drug's effect on glucose.
How insulin sensitivity improves
In five people with active acromegaly, four weeks of 20 mg a day made the liver's glucose output more sensitive to insulin and lowered overnight free fatty acids, while glucose uptake by tissues did not change. A small mechanistic study, not an outcome trial.
Adding it to somatostatin analogues
Across nine studies of patients not controlled on high-dose somatostatin analogues, adding pegvisomant normalised IGF-1 in 66%, lowered fasting insulin without changing glucose or HbA1c, and raised liver enzymes in 14%.
Dosing Data
Somavert starts with a 40 mg loading dose under the skin, then 10 mg a day, adjusted in 5 mg steps between 10 and 30 mg according to IGF-1 measured every four to six weeks.
Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
Side Effects & Contraindications
Reported Side Effects
From the Somavert label (SPL version 13, effective December 18, 2025) and the studies.
Contraindications & Cautions
From the label.
Legal Status
Approved for acromegaly.
Frequently Asked Questions
?How is pegvisomant given?
By daily injection under the skin, titrated by IGF-1 between 10 and 30 mg after a 40 mg loading dose.
?Why is it not dosed by growth hormone levels?
Because it blocks the receptor, growth hormone keeps circulating, and the drug cross-reacts with growth hormone assays; the label says to adjust by IGF-1 only.
?Does it shrink the pituitary tumour?
It is not designed to. In ACROSTUDY most tumours did not change on imaging, about 17% shrank and about 7% grew, which is why the study kept imaging during treatment.
?Does it affect blood sugar?
It tends to improve it, so people on insulin or glucose-lowering tablets may need their doses reduced.
References
- [fda-pi] Somavert (pegvisomant) prescribing information, sections 1, 2, 5, 7 and 12.3 (DailyMed SPL version 13, effective December 18, 2025; read October 1, 2026).
- [pubmed] Trainer PJ, et al. "Treatment of acromegaly with the growth hormone-receptor antagonist pegvisomant." N Engl J Med, 2000;342(16):1171-7. PMID: 10770982.
- [pubmed] Buchfelder M, et al. "Long-term treatment with pegvisomant: observations from 2090 acromegaly patients in ACROSTUDY." Eur J Endocrinol, 2018;179(6):419-427. PMID: 30325178.
- [pubmed] Feola T, et al. "Pegvisomant Improves Glucose Metabolism in Acromegaly: A Meta-Analysis of Prospective Interventional Studies." J Clin Endocrinol Metab, 2019;104(7):2892-2902. PMID: 30869797.
- [pubmed] Higham CE, et al. "Pegvisomant improves insulin sensitivity and reduces overnight free fatty acid concentrations in patients with acromegaly." J Clin Endocrinol Metab, 2009;94(7):2459-63. PMID: 19366854.
- [pubmed] van der Lely AJ, et al. "Long-term safety of pegvisomant in patients with acromegaly: comprehensive review of 1288 subjects in ACROSTUDY." J Clin Endocrinol Metab, 2012;97(5):1589-97. PMID: 22362824.
- [pubmed] Yuen KCJ, et al. "Long-term safety and efficacy of pegvisomant monotherapy for acromegaly: final data from the full ACROSTUDY cohort." Pituitary, 2026;29(3). PMID: 41984268.
- [pubmed] Tritos NA, et al. "Disease-Specific Mortality in Patients With Acromegaly Treated With Pegvisomant: An ACROSTUDY Analysis." Endocr Connect, 2025;14(9). PMID: 40923548.
- [pubmed] Pirchio R, et al. "Control of acromegaly in more than 90% of patients after 10 years of pegvisomant therapy: an European referral centre real-life experience." J Endocrinol Invest, 2023;46(5):1027-1038. PMID: 36892739.
- [pubmed] Kuker AP, et al. "Long-term Pegvisomant Therapy of Acromegaly: Effects on Bone Density, Turnover and Microstructure Using HRpQCT." J Endocr Soc, 2024;8(6):bvae079. PMID: 38715589.
- [pubmed] Lee AP, et al. "Growth hormone receptor antagonism with pegvisomant in insulin resistant non-diabetic men: A phase II pilot study." F1000Res, 2017;6:614. PMID: 28713554.
- [pubmed] Ma L, et al. "Combined therapy of somatostatin analogues with pegvisomant for the treatment of acromegaly: a meta-analysis of prospective studies." BMC Endocr Disord, 2020;20(1):126. PMID: 32811475.
Sources & Citations
Studies were read from their PubMed abstracts; the Somavert label (DailyMed version 13, effective December 18, 2025) was read October 6, 2026.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.