Pegvisomant
The only growth hormone receptor blocker ever approved — a re-engineered growth hormone molecule that occupies its own receptor without switching it on, used daily in acromegaly to force IGF-1 back into the normal range when surgery and somatostatin analogues have failed.
Pegvisomant (Somavert) is a growth hormone look-alike that plugs into the growth hormone receptor without turning it on. Doctors use it for acromegaly, a condition where a pituitary tumour makes far too much growth hormone, and it works by cutting off the signal rather than the hormone. It is a daily injection, it needs regular liver and IGF-1 blood tests, and it is not a bodybuilding or anti-ageing drug — it does the opposite of what growth hormone does.
What is Pegvisomant?
Pegvisomant is growth hormone turned inside out. It carries the same 191-amino-acid backbone as human growth hormone, but nine of those amino acids have been swapped, and one swap in particular — glycine to lysine at position 120 — destroys the molecule's ability to activate the receptor it still binds. The result is a decoy: it docks onto growth hormone receptors on liver and other cells, blocks real growth hormone from getting there, and produces no signal of its own. Several strands of polyethylene glycol are attached to the protein to slow its clearance, pushing the total molecular weight from 22 kDa up to roughly 42 to 52 kDa. Because the liver's production of IGF-1 depends on growth hormone signalling, blocking the receptor collapses circulating IGF-1 — which is precisely the goal in acromegaly, a disease of growth hormone excess. Sold as Somavert, it was approved by the FDA on 25 March 2003 and remains the only growth hormone receptor antagonist on the market anywhere.
What Pegvisomant Is Investigated For
Pegvisomant has one approved job and it does it better than anything else: when a pituitary tumour is still pumping out growth hormone after surgery, radiotherapy or a somatostatin analogue, pegvisomant blocks the receptor downstream and drives IGF-1 into the normal range regardless of how much hormone the tumour makes. That downstream position is both its strength and its limitation — it does nothing to the tumour itself, so imaging surveillance continues, and it cannot be judged by growth hormone levels, which rise on treatment by design. The honest complication is the gap between trial and clinic: 97% of patients treated for a year or more in the registration programme normalised IGF-1, while the 1,464-patient real-world monotherapy cohort in ACROSTUDY reached 62.3%, on a median dose of 15 mg a day against a licensed ceiling of 30 mg. Under-titration, not loss of efficacy, is the widely-accepted explanation. Everything else on the list is secondary: the metabolic benefit is real and reproducible but is a bonus rather than an indication, combination with a somatostatin analogue is common practice built on observational data, and the longevity angle rests entirely on transgenic mice.
History & Discovery
Pegvisomant is one of the few drugs in this directory that was designed rather than found. In the late 1980s John Kopchick's laboratory at Ohio University was making transgenic mice carrying altered growth hormone genes, expecting that a mutation at a conserved glycine would simply weaken the hormone. In 1990 the group reported in PNAS that mice expressing bovine growth hormone with that glycine replaced — position 119 in cattle, equivalent to 120 in humans — were not merely normal-sized but dwarfed, which could only mean the altered hormone was competing with the animals' own growth hormone at the receptor. Follow-up work established why: growth hormone binds its receptor through two separate surfaces in sequence, and the conserved glycine sits at the second one, where any bulkier residue physically prevents the second receptor molecule from docking. Substituting lysine produced a clean antagonist. Turning that insight into a drug took another decade and three companies. The lead molecule, B2036, added eight further substitutions to strengthen site 1 and was shown not to cross-react with the prolactin receptor. Unmodified, it was cleared too quickly to be practical, so polyethylene glycol was attached, producing B2036-PEG. The first-in-human study, published in 1999, confirmed the central pharmacological prediction: a single injection lowered serum IGF-1 without acutely raising growth hormone. Sensus Drug Development ran the clinical programme, Pharmacia acquired it, and Pfizer inherited it — the FDA approval under BLA 021106 on 25 March 2003 still lists Pharmacia as the original sponsor. The twelve-week randomised trial published in the New England Journal of Medicine in April 2000 and the 160-patient long-term extension in the Lancet in November 2001 were both unusually clean, and they set the dosing that is still in use. What followed was less tidy. ACROSTUDY, an international non-interventional registry opened to capture long-term safety, ran for close to two decades and reported its final monotherapy analysis in 2026. Its headline finding was not a safety problem — there were none that changed the label — but an effectiveness gap: clinicians in practice normalised IGF-1 in roughly six patients in ten, on half the licensed maximum dose, where the trials had managed nine in ten. Two decades on, the drug's main unsolved problem is that it is routinely under-used. The discovery had a long coda. The transgenic antagonist mouse line Kopchick's laboratory created in 1991 was maintained continuously, and in 2026 the same group reported that those animals live significantly longer than their littermates — reconnecting a clinical acromegaly drug to the much older observation that disrupting growth hormone signalling is among the most reliable ways to extend life in a mammal.
How It Works
Growth hormone works by grabbing two copies of its receptor and clamping them together, which is what sends the signal inside the cell. Pegvisomant has been engineered to grab the first receptor even more tightly than normal while being completely unable to recruit the second. It therefore sits in the doorway: real growth hormone cannot get in, and no signal gets out. With the liver no longer receiving growth hormone's instructions, it stops making IGF-1 — the hormone that does most of growth hormone's actual work and the one that causes the overgrowth, joint damage and metabolic disease of acromegaly.
Pegvisomant is a recombinant human growth hormone analogue expressed in Escherichia coli and then chemically PEGylated. The protein is 191 amino acids and carries nine substitutions relative to native hGH: His18Asp, Ala21Asn, Gly120Lys, Arg167Asn, Lys168Ala, Asp171Ser, Lys172Arg, Glu174Ser and Ile179Thr. Eight of these lie on binding site 1 and raise its affinity for the growth hormone receptor extracellular domain; the ninth, Gly120Lys, sits at binding site 2 and introduces a bulky charged residue where the second receptor molecule would have to pack, abolishing receptor dimerisation. Because growth hormone receptor signalling requires a sequential 1:2 ligand-to-receptor assembly followed by a conformational change that activates receptor-associated JAK2 and downstream STAT5, occupancy without dimerisation is functionally silent. Loss of JAK2-STAT5 signalling in hepatocytes shuts down transcription of IGF1 and of the other growth-hormone-dependent proteins measured alongside it — free IGF-1, the acid-labile subunit and IGFBP-3 — all of which fall on treatment. Polyethylene glycol polymers of roughly 5 kDa are attached at up to nine probable sites, the amino-terminal phenylalanine plus eight lysines, giving predominant species of about 42, 47 and 52 kDa. PEGylation is a trade-off: it reduces renal clearance, extends the half-life to 60 to 138 hours and blunts immunogenicity, but it also sterically reduces receptor affinity, which is why the therapeutic dose is measured in tens of milligrams a day rather than micrograms. Absorption is slow — peak serum concentrations are not reached for 33 to 77 hours after a subcutaneous dose — and absolute bioavailability is about 57%, with an apparent volume of distribution of only 7 litres and under 1% recovered in urine. One structural consequence matters for research: pegvisomant binds the rodent growth hormone receptor poorly, which is why mechanistic work on growth hormone antagonism in mice has had to use transgenic animals expressing the mutated hormone instead of dosing the human drug.
Evidence Snapshot
Human Clinical Evidence
Strong and unusually long. A 112-patient randomised placebo-controlled dose-ranging trial in the New England Journal of Medicine established efficacy in 2000, a 160-patient open-label study in the Lancet confirmed durability over a mean of 425 days, and FDA approval followed in March 2003. Since then ACROSTUDY has accumulated real-world data on more than two thousand patients, with the final monotherapy analysis covering 1,464 patients treated for a median of six years and followed for a mean of 7.6. Independent meta-analyses of observational cohorts and of metabolic endpoints both exist, and the drug is positioned in the Pituitary Society guidelines and the 2025 acromegaly outcomes consensus.
Animal / Preclinical
Foundational rather than supportive. The entire drug class originated in transgenic mouse work from the Kopchick laboratory showing that a single glycine substitution in growth hormone produced a dwarf phenotype. Because pegvisomant itself binds rodent receptors poorly, subsequent animal work has mostly used those transgenic lines, which in 2026 were shown to live significantly longer than controls.
Mechanistic Rationale
Exceptionally clear. The receptor dimerisation model of growth hormone action is textbook structural biology, the antagonist was designed from it rather than discovered by screening, and the biochemical prediction — occupancy without signalling, falling IGF-1, rising growth hormone — is exactly what is observed in patients.
Research Gaps & Open Questions
What the current literature has not yet settled about Pegvisomant:
- 01Why real-world IGF-1 normalisation is roughly 60% when the registration programme achieved 97%, and whether a protocol that titrated systematically to the 30 mg ceiling would close the gap. The registry data point to under-dosing, but no trial has tested forced titration against usual care.
- 02The mechanism of the opioid interaction. It is documented in the FDA label, reproducible enough to be clinically relevant, and completely unexplained — a rare instance of a labelled interaction with no proposed pathway.
- 03Whether the exon-3-deleted growth hormone receptor variant, or any other genotype, predicts dose requirement well enough to justify testing before treatment. A meta-analysis found a signal; two decades on, nobody genotypes.
- 04Long-term tumour behaviour under sustained receptor blockade. Registry imaging has been reassuring at around 7% growth, but removing IGF-1 feedback from a pituitary adenoma remains a theoretical concern that only longer follow-up can settle.
- 05Whether combination with a somatostatin receptor ligand is genuinely better than optimised monotherapy. Combination is widely practised and supported by observational series, but has never been compared head-to-head with full-dose pegvisomant alone.
- 06Whether growth hormone receptor antagonism has any role outside growth hormone excess. The 2026 mouse lifespan data are striking, and there is scattered preclinical interest in oncology, but pegvisomant's poor rodent receptor affinity has made translation awkward and no human trial outside acromegaly has been undertaken.
- 07How pegvisomant compares with the newer oral somatostatin receptor agonists now reaching the market, which address the same treatment-resistant population from a different direction.
Forms & Administration
Subcutaneous injection once daily, from single-dose vials of lyophilised powder reconstituted with 1 mL of sterile water supplied in a prefilled syringe. Vial strengths are 10, 15, 20, 25 and 30 mg, each reconstituting to that number of milligrams per millilitre. Treatment opens with a 40 mg loading dose given under healthcare supervision, after which patients or caregivers inject daily at home following injection training. Sites are the abdomen, thigh, upper arm or buttock, and rotation genuinely matters here because lipohypertrophy at repeatedly used sites is one of the characteristic adverse effects and can itself alter absorption. Reconstituted solution is for immediate single use. The drug is dispensed through specialty pharmacy channels in most markets and requires an established liver-monitoring plan before the first dose.
Dosing & Protocols
The ranges below reflect protocols commonly discussed in the literature and by clinicians — not a prescription. Actual dosing for any individual should be determined by a qualified healthcare provider who knows the patient.
Typical Range
A 40 mg loading dose given subcutaneously under healthcare supervision, followed from the next day by 10 mg once daily. The dose is then titrated in 5 mg increments or decrements every 4 to 6 weeks to bring serum IGF-1 into the age-adjusted normal range. The licensed range is 10 to 30 mg once daily and the maximum is 30 mg daily, although the real-world median has sat around 15 mg.
Frequency
Once daily, every day, indefinitely while treatment is required.
Timing Considerations
Time of day
Any consistent time of day — the 60-to-138-hour half-life makes the clock irrelevant
Relative to meals
No relationship to food
Relative to exercise
Not tied to exercise timing.
IGF-1 is drawn every 4 to 6 weeks during titration and then at longer intervals; because the drug accumulates slowly, a sample taken too soon after a dose change will understate the effect.
Cycle Length
Continuous. Acromegaly is not cycled; pegvisomant controls the consequences of hormone excess for as long as it is taken, and IGF-1 rises again within weeks of stopping. Registry patients have remained on it for up to 19 years.
Protocol Notes
Three rules govern pegvisomant dosing and all three are counter-intuitive. First, titrate on IGF-1 and nothing else — the label states explicitly that the dose must not be adjusted on growth hormone concentrations or on symptoms, because growth hormone rises on treatment by design and because pegvisomant cross-reacts with some growth hormone assays. Second, measure IGF-1 every four to six weeks during titration and resist moving faster; the slow absorption, with peak concentrations 33 to 77 hours after a dose, and a half-life of 60 to 138 hours mean steady state takes time to establish. Third, do not stop at 10 or 15 mg because IGF-1 has improved. The registry evidence strongly suggests that the gap between trial and clinical results is a titration gap, and the licensed ceiling is 30 mg. Liver tests are obtained before the first dose and on a defined schedule thereafter, and baseline enzymes above three times normal require a work-up before starting at all. Patients on insulin or oral hypoglycaemics should expect those doses to need reducing, sometimes quickly. Patients taking opioids may need higher pegvisomant doses than otherwise comparable patients, for reasons nobody has explained. Reconstituted vials are single-use, injection sites are rotated to avoid lipohypertrophy, and a 30 mg dose given as one injection is bioequivalent to two 15 mg injections, so consolidating is reasonable as the dose climbs.
Pegvisomant is a prescription biologic approved only for acromegaly in patients who have not responded adequately to surgery or radiotherapy. It requires scheduled liver monitoring and IGF-1 titration under specialist endocrine supervision. It has no legitimate use outside that indication, and because it blocks growth hormone action it would be actively counterproductive for any body-composition or performance purpose.
Timeline of Effects
Onset
IGF-1 begins falling within the first week and the biochemical trajectory is clear within a month, which is why titration intervals are set at four to six weeks. Symptomatic change lags: in the registration trial significant improvements in ring size, soft-tissue swelling, perspiration and fatigue were recorded over twelve weeks at the two higher doses. Glucose and insulin sensitivity improve early and independently of how far IGF-1 has moved.
Peak Effect
Maximum biochemical effect arrives when the dose has been titrated to a normal IGF-1, which in practice takes two to six months of 5 mg steps. Soft-tissue and metabolic improvements continue accruing over the first year. Skeletal changes already established by years of untreated acromegaly — jaw, brow, hands and feet — do not reverse; what resolves is the soft-tissue swelling layered on top of them.
After Discontinuation
Reversal is complete and relatively quick. Growth hormone, which had risen while the receptor was blocked, fell back to baseline within 30 days of withdrawal in the 45 patients withdrawn during the original long-term study, and IGF-1 climbs back toward pre-treatment levels on a similar timescale. Because the drug never touched the tumour, nothing about the underlying disease has changed — stopping pegvisomant returns a patient to their untreated acromegaly.
Monitoring & Measurement
Bloodwork & Labs
- •Serum IGF-1, age- and sex-adjusted — the sole titration target, measured every 4 to 6 weeks during dose adjustment and at longer intervals once stable
- •ALT, AST, total bilirubin and alkaline phosphatase — baseline before the first dose, then monthly for 6 months, quarterly for the next 6 and twice over the following year when baseline values are normal, with monthly testing for at least a year when baseline enzymes are mildly raised
- •Fasting glucose and HbA1c, particularly in the first months, because insulin sensitivity improves and antidiabetic doses often need reducing
- •Growth hormone — measured for completeness and to track the expected rise, but explicitly not used for dosing, and interpreted with knowledge of whether the assay cross-reacts with pegvisomant
- •Anti-growth-hormone antibodies, which appeared in about 17% of patients in the long-term study without loss of efficacy and are not routinely needed outside research settings
Functional & Performance Tests
- •Pituitary MRI at intervals set by the treating centre — mandatory surveillance, because the drug does not act on the adenoma
- •Ring size and shoe size, which sound unscientific but were formal endpoints in the registration trial and remain the most sensitive everyday measure of soft-tissue response
- •Blood pressure and sleep-apnoea assessment, both of which are acromegaly comorbidities tracked in the global registry
- •Echocardiography and joint assessment where cardiac or arthropathic complications of acromegaly are established
- •Inspection and palpation of injection sites at every review, specifically for lipohypertrophy
When to Test
Baseline IGF-1, liver tests, glucose and HbA1c, plus a current pituitary MRI, before the loading dose. IGF-1 and liver tests every 4 to 6 weeks and monthly respectively through the titration phase. Once IGF-1 has normalised on a stable dose, IGF-1 moves to roughly 6-monthly and liver tests to the schedule the label sets out by baseline category. MRI frequency is set by tumour size and prior treatment, not by the drug.
Interpretation & Notes
The discipline that makes pegvisomant work is titration, and the discipline that makes it safe is liver surveillance; neither is optional and the registry data suggest the first is the one clinicians skimp on. Interpreting the numbers takes some care. A falling IGF-1 that has not reached the age-adjusted normal range is an undertreated patient, not a responder — the 5 mg step exists to be used, repeatedly, up to 30 mg. A rising growth hormone is reassurance that the blockade is working. An isolated transaminase rise is common, usually transient, and typically appears within 4 to 12 weeks of starting; it is not dose-related, so reducing the dose is not the answer, and the label's tables set out when to continue with closer monitoring and when to stop. Patients should be warned that improving blood sugar is a likely early event so that hypoglycaemia on unchanged diabetes medication does not come as a surprise. Finally, every IGF-1 result should be drawn in the same laboratory where possible: IGF-1 assays differ enough between platforms that switching mid-treatment can look like a response that never happened.
Common Questions
How can a growth hormone molecule block growth hormone?
Growth hormone has to bind its receptor twice to work. One face of the molecule — site 1 — grabs the first receptor with high affinity; a second face, site 2, then recruits a second receptor, and only that paired arrangement transmits a signal into the cell. Pegvisomant keeps site 1, strengthened by eight amino acid substitutions, and has site 2 deliberately wrecked by replacing glycine 120 with lysine. So it binds a receptor firmly and then goes no further. The receptor is occupied, real growth hormone is locked out, and nothing happens. The discovery came from Kopchick's laboratory at Ohio University in the early 1990s, which found that mutating the conserved glycine — position 119 in bovine growth hormone, 120 in human — converted the hormone from an agonist into an antagonist, and that transgenic mice carrying the mutated gene grew to dwarf size.
Why does my growth hormone level go up on pegvisomant?
Because the feedback loop has been cut. Normally IGF-1 produced by the liver tells the pituitary to ease off. Pegvisomant stops the liver responding to growth hormone, IGF-1 falls, the pituitary senses the shortfall and secretes more growth hormone — which the receptor blockade renders inert. Rising growth hormone on pegvisomant is therefore expected pharmacology, not treatment failure, and it is the reason the label states explicitly that dosage must not be adjusted on growth hormone concentrations or on symptoms. There is a second trap: pegvisomant cross-reacts with some growth hormone immunoassays, so a reported growth hormone number may be measuring the drug. IGF-1 is the only valid titration target.
What does the liver monitoring involve?
Alanine aminotransferase, aspartate aminotransferase, total bilirubin and alkaline phosphatase are measured before the first dose, then monthly for the first six months, quarterly for the next six and twice over the following year if baseline values were normal. Baseline enzymes above three times the upper limit of normal require a full work-up before starting. In the pre-approval programme, asymptomatic transient transaminase rises of up to 15 times normal occurred in under 2% of patients and resolved, usually after suspending treatment; post-marketing reports include elevations above 20 times normal with bilirubin above twice normal. In the real-world ACROSTUDY monotherapy cohort, raised transaminases were reported as a treatment-related event in 1.2% of 1,464 patients over a median six years.
Does pegvisomant shrink the pituitary tumour?
No, and that is the main reason it is not a universal first choice. Pegvisomant acts on receptors in the periphery and has no effect on the adenoma, so tumour surveillance by MRI continues throughout treatment. Removing IGF-1 feedback was theorised to allow tumour regrowth, and the long-term data have been broadly reassuring rather than entirely silent: tumour volume did not increase significantly across 131 patients followed for a mean of 11.5 months in the original long-term study, and in the final ACROSTUDY analysis 7.2% of 1,248 imaged patients had an increase in tumour size — a figure in line with the 7.3% estimated in an independent meta-analysis of observational cohorts.
Is pegvisomant banned in sport?
It is not named anywhere on the WADA Prohibited List, and its biological effect is the opposite of doping — it lowers IGF-1 rather than raising it, so there is no plausible performance rationale. The complication is textual rather than pharmacological. Class S2.2.3 prohibits 'Growth hormone (GH), its analogues and fragments', and the chapeau to S2 extends the ban to substances 'with similar chemical structure or similar biological effect'. Pegvisomant is described in its own FDA label as an analog of human growth hormone and differs from the real hormone at nine residues, so a literal reading of the structural limb captures it even though the biological limb clearly does not. An athlete prescribed pegvisomant for acromegaly should treat the question as unsettled and clear it with their anti-doping organisation rather than assume either answer.
Who Pegvisomant Is NOT For
- •None are listed in the US label, which is unusual for an injectable biologic and reflects that the dose-limiting problems are handled by monitoring rather than by excluding patient groups. The entries below are therefore cautions that function as practical contraindications rather than formal ones.
- •Baseline liver tests above three times the upper limit of normal. Treatment should not start until a comprehensive work-up has established the cause of the abnormality.
- •Known hypersensitivity to pegvisomant or to any component, including latex in the diluent syringe components of some presentations. Systemic hypersensitivity reactions have been reported, and re-initiation afterwards requires close supervision.
- •Pregnancy and breastfeeding are not absolute bars but are inadequately studied; management in pregnancy rests on narrative reviews and case series rather than trials, and decisions belong with a specialist pituitary centre.
- •Use for any purpose other than growth hormone excess. Blocking the growth hormone receptor in a person with normal growth hormone physiology produces iatrogenic growth hormone deficiency, and in a child would impair growth.
- •Patients who cannot or will not commit to the liver-test schedule and periodic IGF-1 measurement, since both are integral to safe dosing rather than optional extras.
Drug & Supplement Interactions
Two interactions appear in the label and one of them is genuinely strange. The straightforward one is with insulin and oral hypoglycaemic agents: growth hormone opposes insulin's effect on carbohydrate metabolism, so removing growth hormone signalling improves insulin sensitivity and glucose tolerance, and patients with acromegaly and diabetes frequently need their antidiabetic doses reduced after starting pegvisomant to avoid hypoglycaemia. The meta-analytic data put numbers on the magnitude — fasting glucose down 0.80 mmol/L and HbA1c down 0.43% — and show the effect is not merely a consequence of disease control, since it does not track the change in IGF-1. The odd one is with opioids. Across the clinical studies, patients taking opioids consistently needed higher pegvisomant doses, and higher serum pegvisomant concentrations, to achieve the same IGF-1 suppression. The mechanism is unknown and the label says so. It has practical consequences: a patient with acromegaly on chronic opioid analgesia who appears refractory at 20 mg may simply require more drug rather than a change of strategy. Beyond these, pegvisomant's most consequential interference is analytical rather than pharmacological — it cross-reacts with some growth hormone immunoassays, so laboratory results must be interpreted with the assay's specificity in mind. The drug is not metabolised by cytochrome P450 enzymes, has an apparent volume of distribution of only 7 litres, and is cleared by routes that have not been characterised in humans, so classical pharmacokinetic drug interactions are not expected.
Safety Profile
Common Side Effects
Cautions
- • Liver injury is the signal that drives the monitoring schedule. Transaminase elevations are usually transient and asymptomatic, but post-marketing cases above 20 times the upper limit of normal with raised bilirubin have occurred, and discontinuation generally produced improvement or resolution.
- • Hypoglycaemia in people with diabetes. Growth hormone opposes insulin, so blocking it improves insulin sensitivity — insulin and oral hypoglycaemic doses often need reducing, and this is listed in the label as an interaction rather than a side effect.
- • Pegvisomant cross-reacts with some growth hormone immunoassays, which can produce falsely elevated readings and mislead anyone titrating on the wrong marker.
- • Systemic hypersensitivity reactions have been reported; re-initiation after such a reaction requires close monitoring.
- • The drug does not touch the tumour, so patients remain under imaging surveillance regardless of how well IGF-1 is controlled.
- • Antibodies to growth hormone were detected in about 17% of patients in the original long-term study, but no loss of effect over time was seen.
- • The US label lists no contraindications at all, which is unusual and should not be read as an absence of risk — it reflects the fact that the dose-limiting problems are managed by monitoring rather than by excluding patients.
What We Don't Know
Pegvisomant has one of the longest real-world safety records of any peptide drug in this directory — nearly two decades of registry follow-up in more than two thousand patients — so the open questions are mostly about effectiveness rather than harm. The central one is why real-world IGF-1 normalisation sits around 60% when the trials achieved 97%, and whether systematically titrating to the licensed 30 mg ceiling would close the gap. Pharmacogenetics is unresolved: a meta-analysis found that carriers of the exon-3-deleted growth hormone receptor variant respond differently, but the effect has not changed practice. The interaction with opioids, in which patients taking them need higher pegvisomant doses to normalise IGF-1, is documented in the label and remains mechanistically unexplained. And because the drug entered the market in 2003 without a mortality endpoint, questions about long-term cancer surveillance and pregnancy exposure are being answered retrospectively from registry data.
Legal Status
United States
FDA-approved prescription biologic (Somavert, BLA 021106, approved 25 March 2003 to Pharmacia, now marketed by Pfizer). Indicated for acromegaly in patients who have had an inadequate response to surgery or radiation therapy, or for whom those therapies are not appropriate, with the stated treatment goal of normalising serum IGF-1. Supplied as 10, 15, 20, 25 and 30 mg single-dose vials, all currently marketed. It is not a controlled substance and not a compounding-pharmacy product; it is dispensed through specialty channels with a liver-monitoring requirement. There is no FDA-approved use in children, in growth promotion, or in any metabolic or body-composition indication.
International
Approved in the European Union, the United Kingdom, Japan and many other markets as Somavert, with indication wording closely aligned to the US label. A dedicated Japanese phase 3 monotherapy study was conducted to support registration there. Availability is generally restricted to specialist pituitary or endocrine centres.
Sports & Competition
Not named anywhere on the WADA Prohibited List, and pharmacologically the opposite of a doping agent — it lowers IGF-1 instead of raising it, so there is no performance rationale for using it. The caveat is textual. Class S2.2.3 prohibits 'Growth hormone (GH), its analogues and fragments' and the introduction to S2 extends the prohibition to substances with similar chemical structure or similar biological effect. Pegvisomant is formally an analogue of human growth hormone, differing at nine residues, so the structural limb of that wording arguably captures it while the biological limb plainly does not. No published decision resolves the point. An athlete prescribed pegvisomant should treat it as an open question and obtain written guidance from their anti-doping organisation rather than relying on its absence from the list.
Regulatory status changes over time. Verify current local rules with a qualified professional.
Myths & Misconceptions
Myth
Pegvisomant is a growth hormone drug, so it builds muscle.
Reality
It does the exact opposite. Pegvisomant occupies the growth hormone receptor and blocks it, driving IGF-1 down rather than up. In someone with normal growth hormone physiology it would produce iatrogenic growth hormone deficiency. Its chemical kinship with growth hormone is a design feature of the decoy, not a hint at shared effects.
Myth
Rising growth hormone levels mean the drug has stopped working.
Reality
Rising growth hormone is the expected signature of a working receptor blockade. IGF-1 falls, the pituitary loses its negative feedback and secretes more growth hormone, and that extra hormone cannot signal because the receptors are occupied. The label forbids adjusting the dose on growth hormone values, and some assays measure the drug itself as if it were growth hormone. IGF-1 is the only valid marker.
Myth
Because it blocks growth hormone, pegvisomant must worsen blood sugar.
Reality
The reverse. Growth hormone is a counter-regulatory hormone that reduces insulin sensitivity, so blocking it improves glucose metabolism — a 13-study meta-analysis found lower fasting glucose, HbA1c and HOMA-IR, independent of IGF-1 change. The clinical consequence is that patients with diabetes often need their insulin or oral agents reduced, and hypoglycaemia rather than hyperglycaemia is the labelled risk.
Myth
A normal IGF-1 means the pituitary tumour is under control.
Reality
Pegvisomant works downstream of the tumour and has no effect on it at all. A patient can have a perfectly normal IGF-1 while the adenoma grows, which is why MRI surveillance continues regardless of biochemical control. This is the single most important practical difference between pegvisomant and the somatostatin analogues, which do act on the tumour.
Myth
Two decades of registry data showing 60% control means the drug is only moderately effective.
Reality
It means the drug is moderately well used. The registration trials reached 97% IGF-1 normalisation, the registry reached 62.3%, and the median registry dose was 15 mg a day against a licensed maximum of 30. An independent meta-analysis reached the same conclusion from different cohorts. The gap is a prescribing gap, and recognising that is why the guidelines now stress titration to effect.
Published Research
34 studiesGrowth Hormone Receptor Antagonism Extends Lifespan
From the laboratory that discovered the antagonist. Because pegvisomant binds rodent receptors poorly it cannot be tested for longevity in mice, so the group used the transgenic antagonist line it has maintained since 1991. Median and maximal lifespan both rose significantly in males — by 186 and 265 days — and two-year-old animals of both sexes were less frail with better grip strength, despite carrying more fat. It is the strongest evidence yet that blocking growth hormone extends healthspan, and it is still entirely a mouse result.
Management and safety of somatostatin receptor ligands and pegvisomant in pregnant women with acromegaly: a narrative review
Long-term safety and efficacy of pegvisomant monotherapy for acromegaly: final data from the full ACROSTUDY cohort
The definitive real-world dataset: 1,464 patients on pegvisomant monotherapy for a median of 6.0 years, maximum 19.3, followed a mean of 7.6 years. IGF-1 normalisation at last observation was 62.3% on a median dose of 15 mg/day against a licensed maximum of 30. Serious adverse events affected 19.3%; the commonest treatment-related events were raised IGF-1 (1.8%), lipohypertrophy (1.2%) and raised transaminases (1.2%). There were 31 deaths, none attributed to treatment, and 7.2% of imaged patients showed tumour growth. Two authors are Pfizer employees and stockholders.
Pegvisomant in managing comorbidities of acromegaly: a review
Disease-Specific Mortality in Patients With Acromegaly Treated With Pegvisomant: An ACROSTUDY Analysis
Consensus on acromegaly therapeutic outcomes: an update
The 2025 update to the field's outcome definitions, and the document that frames what counts as treatment success now that several medical options exist. Useful for reading the pegvisomant registry numbers in context, since 'disease control' has been defined differently across the two decades of published cohorts.
Growth hormone receptor antagonist pegvisomant and its role in the medical therapy of growth hormone excess
Standards of care for medical management of acromegaly in pituitary tumor centers of excellence (PTCOE)
Factors associated with disease control failure in acromegaly patients treated with pegvisomant: an ACROSTUDY analysis
Efficacy and Safety of Pegvisomant in the Treatment of Acromegaly
Approach to the Patient With Treatment-resistant Acromegaly
Patient-reported outcomes in patients with acromegaly treated with pegvisomant in the ACROSTUDY extension
More than a decade of real-world experience of pegvisomant for acromegaly: ACROSTUDY
Body Composition Changes with Long-term Pegvisomant Therapy of Acromegaly
Hypertension in Acromegaly in Relationship to Biochemical Control and Mortality: Global ACROSTUDY Outcomes
A Pituitary Society update to acromegaly management guidelines
Places pegvisomant as the agent to reach for when IGF-1 remains elevated on a somatostatin receptor ligand, and codifies the rules that make it unusual to prescribe: titrate on IGF-1 only, never on growth hormone, and continue tumour imaging because the drug acts downstream of the adenoma.
All-cause mortality in patients with acromegaly treated with pegvisomant: an ACROSTUDY analysis
Pegvisomant Improves Glucose Metabolism in Acromegaly: A Meta-Analysis of Prospective Interventional Studies
Thirteen studies and 550 subjects. Pegvisomant lowered fasting plasma glucose by 0.80 mmol/L, HbA1c by 0.43% and HOMA-IR by 0.61, and the effects on glucose and insulin were not correlated with the change in IGF-1 — meaning the metabolic benefit is a direct consequence of removing growth hormone's anti-insulin action rather than a by-product of disease control. Added to a somatostatin analogue, it offset that drug's adverse metabolic effect to produce an overall neutral result.
Diabetes in patients with acromegaly treated with pegvisomant: observations from ACROSTUDY
Long-term treatment with pegvisomant: observations from 2090 acromegaly patients in ACROSTUDY
Effectiveness and safety of pegvisomant: a systematic review and meta-analysis of observational longitudinal studies
The independent counterweight to the registration data. Pooling 14 observational cohorts, overall disease control was 60.9% and control on monotherapy 71.7%, with tumour growth estimated at 7.3% and transaminase elevation at 3.0%. The authors state plainly that real-world effectiveness is lower than interventional studies reported — a conclusion the final ACROSTUDY analysis later reproduced almost exactly.
Effectiveness of first-line pegvisomant monotherapy in acromegaly: an ACROSTUDY analysis
The Effect of the Exon-3-Deleted Growth Hormone Receptor on Pegvisomant-Treated Acromegaly: A Systematic Review and Meta-Analysis
Examined whether the common exon-3-deleted growth hormone receptor polymorphism predicts response to receptor blockade. The signal is real enough to keep appearing in the literature but has never been strong or consistent enough to justify genotyping before treatment, which is why titration remains empirical.
Efficacy and safety of monotherapy by pegvisomant, a growth hormone receptor antagonist, in Japanese patients with acromegaly
Long-term treatment with pegvisomant for acromegaly: a 10-year experience
Combined treatment of somatostatin analogues with pegvisomant in acromegaly
Long-term treatment with pegvisomant as monotherapy in patients with acromegaly: experience from ACROSTUDY
Combination treatment with somatostatin analogues and pegvisomant in acromegaly
Discovery and mechanism of action of pegvisomant
Long-term treatment of acromegaly with pegvisomant, a growth hormone receptor antagonist
160 patients treated for an average of 425 days, with 152 analysed for efficacy. Of those treated 12 months or longer, 87 of 90 — 97% — achieved a normal IGF-1, while growth hormone rose as predicted by the loss of feedback. Antibodies to growth hormone appeared in 16.9% of patients with no tachyphylaxis. Two patients had progressive pituitary tumour growth and two withdrew for transaminase elevation; mean tumour volume across 131 patients followed a mean of 11.5 months did not change significantly. The 97% figure is the benchmark against which every real-world cohort since has looked disappointing.
Binding and functional studies with the growth hormone receptor antagonist, B2036-PEG (pegvisomant), reveal effects of pegylation
Quantified the central engineering trade-off: attaching polyethylene glycol extends the half-life and reduces immunogenicity but sterically lowers affinity for the growth hormone receptor, which is why pegvisomant has to be dosed in tens of milligrams daily rather than at the microgram scale its unmodified protein potency would suggest.
Treatment of acromegaly with the growth hormone-receptor antagonist pegvisomant
The registration trial. 112 patients with acromegaly randomised to placebo or pegvisomant 10, 15 or 20 mg daily for 12 weeks. IGF-1 fell by 26.7%, 50.1% and 62.5% across the three dose groups against 4.0% on placebo, and normalised in 54%, 81% and 89% of patients versus 10%. Ring size, soft-tissue swelling, perspiration and fatigue all improved at the two higher doses, and adverse event rates were similar across groups. This is the dose-response curve the 10-to-30 mg titration range was built on.
Growth hormone (GH) receptor blockade with a PEG-modified GH (B2036-PEG) lowers serum insulin-like growth factor-I but does not acutely stimulate serum GH
Expression of a mutated bovine growth hormone gene suppresses growth of transgenic mice
The origin of the drug. Transgenic mice expressing bovine growth hormone with a substitution at the conserved glycine — position 119 in cattle, 120 in humans — were smaller than their littermates rather than larger, demonstrating that the altered hormone was acting as an antagonist at the receptor. Every growth hormone receptor blocker since traces to this result.
Quick Facts
- Class
- Growth Hormone Receptor Antagonist
- Tier
- B
- Evidence
- Strong
- Safety
- Well-Studied
- Updated
- Oct 2026
- Citations
- 34PubMed
Also known as
Tags
Evidence Score
Clinical Trials
View Clinical TrialsLinks to ClinicalTrials.gov for reference. Listing does not imply endorsement.