Skip to content
For research use only. Not for human or veterinary use. Not a drug, food, or dietary supplement.
AMIRAVOResearch Library

IGF-1 LR3 vs PEG-MGF

IGF-1 LR3 and PEG-MGF are both derived from insulin-like growth factor 1 but in different ways, and neither has been tested in a registered human trial 4,10. IGF-1 LR3 (Long [Arg3]-IGF-I) is a recombinant fusion analogue created as a laboratory reagent, with an N-terminal extension from porcine growth hormone and arginine replacing glutamate at position 3 1. PEG-MGF is a pegylated form of mechano growth factor, the 24-amino-acid C-terminal peptide of the IGF-1Ec splice variant 6,8. The FDA lists PEG-MGF among bulk substances for compounding that may present significant safety risks and states it has identified no human exposure data; IGF-1 LR3 is not named on that page, as of 22 April 2026 9.

Unbranded reference vial illustrating IGF-1 LR3; not an actual product
IGF-1 LR3
Not approved — research use only
Unbranded reference vial illustrating PEG-MGF; not an actual product
PEG-MGF
Not approved — research use only

Side by side

FieldIGF-1 LR3PEG-MGF
ClassRecombinant IGF-1 fusion analogue with reduced binding to IGF-binding proteins 1Pegylated synthetic peptide corresponding to the C-terminal E domain of the IGF-1Ec (MGF) splice variant 6,8
Origin and structureLong [Arg3]-IGF-I: IGF-I with the first 11 amino acids of methionyl porcine growth hormone plus Val-Asn at the N terminus and Arg substituted for Glu-3, expressed in E. coli 1. A black-market vial was identified as His-tagged Long-R3-IGF-I, a form usually made for biochemical studies 3MGF is the 24-residue C-terminal peptide cleaved from unprocessed IGF-1Eb/Ec; pegylation is added to extend its presence in circulation 6,7
Proposed mechanismActs at the IGF-I receptor with poor binding to IGF-binding proteins, which in cell and animal work increased potency and duration relative to native IGF-I 1,2Proposed to promote muscle satellite-cell proliferation and delay myoblast fusion, possibly independently of the IGF-1 receptor; two pharmaceutical laboratories could not reproduce these effects in cells 6,8
Half-lifeNot located; in pigs, IGF-I variants including LR3-IGF-I suppressed plasma glucose for much longer than native IGF-I (animal data) 2Not located in the sources reviewed
Highest human trial phaseNo registered study located (ClinicalTrials.gov searched 24 October 2026) 4No registered study of PEG-MGF located; related searches returned only unrelated pegylated growth hormone products 4,9
FDA statusNot FDA-approved and not named on the FDA compounding page as of 22 April 2026 9. Recombinant IGF-1 itself is approved as mecasermin (INCRELEX, BLA 021839), a different molecule 5Not FDA-approved; listed as mechano growth factor pegylated (PEG-MGF) among bulk substances that may present significant safety risks (nomination withdrawn), as of 22 April 2026 9
Published human outcomesNone located; published work is in cells, pigs and marmoset monkeys, plus one black-market product analysis 1,2,3None located; human work concerns expression of IGF-1 isoforms after exercise-induced muscle damage, not administration of PEG-MGF 8
Safety signalsNot located for humans; in pigs and marmosets, IGF-I variants lowered plasma glucose more and for longer than native IGF-I (animal data) 2. The authors of the black-market analysis note that the effects of His-tagged Long-R3-IGF-I in humans have not been described 3FDA states it has identified no human exposure data for PEG-MGF by any route and lacks information on whether it would cause harm 9
WADA statusCovered under S2.3, which names IGF-1 (mecasermin) and its analogues; prohibited at all times (2026 List) 11Covered under S2.3, which names mechano growth factors (MGFs); prohibited at all times (2026 List) 11
Who funded the evidenceAustralian CSIRO-linked academic groups developed and tested the analogues 1,2; the product analysis came from a German anti-doping laboratory 3The negative replication work was done at Novartis and a second pharmaceutical company 6; characterisation work came from anti-doping laboratories 7

IGF-1 LR3: what the data says

IGF-1 LR3 originated as a research reagent. In rat myoblasts and hepatoma cells (cell data), Long [Arg3]-IGF-I and related fusion analogues were more potent than native IGF-I at stimulating protein and DNA synthesis 1.

  • In pigs and marmoset monkeys (animal data), variants with poor IGF-binding-protein affinity, including LR3-IGF-I, lowered plasma glucose 2- to 3-fold more potently than IGF-I and for substantially longer 2.
  • An anti-doping laboratory identified His-tagged Long-R3-IGF-I in a black-market injection vial and noted that this form is usually produced for biochemical studies, with effects in humans not described 3.
  • No registered human study was located 4. Recombinant IGF-1 is approved as mecasermin, a different molecule without the Long R3 modifications 5.

PEG-MGF: what the data says

MGF refers to the C-terminal peptide of an IGF-1 splice variant that is up-regulated after exercise or injury 6,8. The claimed cell-level effects have been contested.

  • Researchers at two pharmaceutical companies could not reproduce reported MGF effects on human or mouse myoblast proliferation, differentiation, or signalling in cardiac myocytes, while mature IGF-1 produced clear responses (cell data) 6.
  • In 10 healthy men after exercise-induced muscle damage (humans), MGF mRNA rose transiently; separate cell experiments suggested synthetic MGF E peptide may act without the IGF-1 receptor 8.
  • Anti-doping laboratories have characterised a 'full-length MGF' product offered through illicit channels, reflecting availability outside regulated supply 7.
  • FDA states it has identified no human exposure data for PEG-MGF by any route 9. A 2026 review groups both compounds among unregulated GH-IGF-1 axis agents marketed as research compounds 10.

Key research differences

  • Molecule: IGF-1 LR3 is a full IGF-I analogue with an N-terminal extension 1, whereas MGF is a short C-terminal peptide from an IGF-1 splice variant 6.
  • Mechanistic support: IGF-1 LR3's receptor activity is documented in cells and animals 1,2, while attempts at two pharmaceutical companies failed to reproduce MGF's cell effects 6.
  • FDA listing: PEG-MGF is named on the FDA compounding page with no identified human exposure data, while IGF-1 LR3 is not named there 9.
  • Observable animal effects: LR3-IGF-I produced pronounced and prolonged glucose lowering in pigs and marmosets 2; no comparable in vivo pharmacodynamic data for PEG-MGF were located 9.

Where the evidence is limited

Neither compound has a registered human trial, so no clinical comparison is possible 4,9. IGF-1 LR3 data come from cell lines, pigs and marmosets, and the material sold under this name has been found to be a His-tagged laboratory reagent whose human effects are undescribed 1,2,3. For PEG-MGF, the underlying MGF cell-level claims were not reproduced by two pharmaceutical laboratories, and the pegylated form has no identified human exposure data 6,9. Product identity is a recurring problem for both, as anti-doping laboratories' analyses of illicit material show 3,7.

Frequently asked questions

Is IGF-1 LR3 the same as approved IGF-1?
No. The approved product is mecasermin (INCRELEX), recombinant human IGF-1 5. IGF-1 LR3 is a fusion analogue with an N-terminal extension and an Arg substitution that reduce binding to IGF-binding proteins 1.
Does MGF build muscle?
The claimed cell effects were not reproduced: researchers at two pharmaceutical companies found no effect of MGF peptides on human or mouse myoblast proliferation or differentiation, while mature IGF-1 did act 6. No human administration study was located 9.
Can IGF-1 LR3 and PEG-MGF be compared directly?
No. Neither has a registered human trial, and their preclinical data come from different models and endpoints 4,6,9.
Are they prohibited in sport?
Both fall under WADA's S2.3, which names IGF-1 and its analogues and mechano growth factors; the class is prohibited at all times 11.

References

  1. Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency Journal of Molecular Endocrinology. 1992
  2. IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in pigs and marmoset monkeys Journal of Endocrinology. 1997
  3. Detection of His-tagged Long-R3-IGF-I in a black market product Growth Hormone & IGF Research. 2010
  4. ClinicalTrials.gov API search for "long R3" IGF (0 studies returned, 24 October 2026) ClinicalTrials.gov. 2026
  5. Drugs@FDA (openFDA) record for mecasermin (INCRELEX, BLA 021839, Ipsen) FDA openFDA. 2026
  6. Mechano-growth factor peptide, the COOH terminus of unprocessed insulin-like growth factor 1, has no apparent effect on myoblasts or primary muscle stem cells American Journal of Physiology: Endocrinology and Metabolism. 2014
  7. Mass spectrometric characterization of a biotechnologically produced full-length mechano growth factor (MGF) relevant for doping controls Growth Hormone & IGF Research. 2014
  8. Expression of IGF-1 isoforms after exercise-induced muscle damage in humans: characterization of the MGF E peptide actions in vitro In Vivo. 2009
  9. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (content current as of 04/22/2026) FDA (Human Drug Compounding). 2026
  10. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration Frontiers in Endocrinology. 2026
  11. Prohibited List 2026 (in force 1 January 2026) World Anti-Doping Agency. 2026

For research use only. Not for human or veterinary use. Not a drug, food, or dietary supplement. This page compares published research and is not medical advice or a recommendation.