Is there an approved IGF-1 medicine?

Yes — mecasermin, marketed as Increlex, is recombinant human IGF-1 administered subcutaneously. It is native rhIGF-1, not LR3.

Does that approval cover LR3?

No. LR3 is a different molecule with different binding behaviour and holds no marketing authorisation anywhere.

Why wasn't LR3 developed clinically?

Its modifications bypass a regulatory system rather than an obstacle. Its development context was cell culture, where systemic regulation is not a consideration.

IGF-1 LR3

IGF-1 LR3 Against the Native Hormone

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-234 cited sources

Native IGF-1 is 70 residues and binds IGF binding proteins with high affinity. LR3 is 83 residues and largely does not. A recombinant native IGF-1 is an approved medicine — mecasermin, marketed as Increlex. LR3 is not that molecule and is approved nowhere.

Key facts

Native IGF-1: 70 residues, ~7.6 kDa
IGF-1 LR3: 83 residues
Native IGFBP binding: High affinity
LR3 IGFBP binding: Substantially reduced
Approved native product: Mecasermin (Increlex), subcutaneous
Approved LR3 product: None

The structural difference

Thirteen extra residues at the N-terminus and one substitution at position 3. That is the whole of it — the folded core and the three disulfide bonds are otherwise the native architecture. A modest change by residue count, aimed precisely at one interaction.

The functional difference

Native IGF-1 in circulation is almost entirely sequestered by binding proteins. LR3 largely escapes that, which raises its free fraction substantially at the same total concentration. The receptor engagement is not fundamentally different; the availability is.

Research material referenced

IGF-1 LR3 1mg — third-party HPLC tested

View — £37.99

The regulatory difference, which is the important one

Mecasermin is recombinant human IGF-1 with an FDA-approved label, marketed as Increlex and administered subcutaneously. It has been used in severe primary IGF-1 deficiency — Petriczko and colleagues reported on this in 2019, and Denaite and colleagues described patient characteristics and treatment efficacy in Frontiers in Pediatrics in 2024. That is a licensed medicine with an indication and an evidence base.

And LR3 is not it

The approved product is native rhIGF-1. LR3 is an engineered analogue with different binding behaviour, no marketing authorisation anywhere, and no clinical development programme. The existence of an approved IGF-1 medicine does not extend to it in any respect, and conflating the two is the most consequential error available in this category.

Why the modification was not pursued clinically

The binding protein system is not merely an obstacle — it regulates a growth factor with receptors on essentially every tissue. An analogue engineered to bypass that regulation removes a control mechanism rather than a nuisance. Its development context was cell culture, where controlled availability in a dish is the goal and systemic regulation is not a consideration.

Prohibited status applies to both

IGF-1 and its analogues appear on the WADA Prohibited List under class S2, prohibited at all times in and out of competition. That covers native and engineered forms alike.

Extended research context

The IGF-1 LR3 deep dive

Deep dive: the design that runs backwards from everything else here

Almost every engineered compound in this catalogue solves the same problem in the same direction. Semaglutide attaches a C18 diacid, retatrutide and tirzepatide a C20, all to bind serum albumin and extend duration. CJC-1295's DAC goes further and binds albumin covalently at Cys34. The strategy throughout is to add binding, so the molecule survives longer in circulation. IGF-1 LR3 does the reverse. Its two modifications - arginine replacing glutamate at position 3, and a thirteen-residue N-terminal extension - exist to REMOVE binding, specifically to the IGF binding proteins that sequester the overwhelming majority of circulating IGF-1 in a ternary complex with IGFBP-3 and the acid-labile subunit. Same bound-free equilibrium, engineered in the opposite direction. The reason is that the two families face opposite constraints: an incretin peptide is cleared too fast to be useful, while IGF-1 is held too tightly to be available. Baxter's 1994 review in Hormone Research is the standard account of just how tightly.

Deep dive: a certificate written for the wrong failure mode

This is a recombinant protein, and it fails differently from everything else on this site. A synthetic peptide accumulates deletion sequences, because each coupling is slightly less than complete - at 99% efficiency a 39-mer finishes around 68% full-length, and those impurities differ by one residue's mass and show up in a mass spectrum. Ribosomal synthesis does not fail that way at all; a host cell builds the protein correctly or not at all. What contaminates the product instead is everything else the cell contained: host cell proteins, host DNA, and in bacterial systems endotoxin, which is not a protein, does not appear in a protein purity figure, and needs its own assay entirely. Layered on top is a failure mode with no peptide equivalent. This protein has three disulfide bonds, meaning six cysteines that can pair fifteen ways of which one is correct - and Milner and colleagues showed in the Biochemical Journal in 1995 that B-domain mutations influence oxidative folding, which is directly relevant since position 3 sits in the B-domain. A misfolded isomer has identical mass, identical composition, and is invisible to mass spectrometry. A certificate reading exactly like a synthetic peptide's is testing for problems this production route does not have while missing the ones it does.

Deep dive: an approved relative, and why that raises the risk rather than lowering it

Unusually for this catalogue, a licensed IGF-1 medicine exists. Mecasermin, marketed as Increlex, is recombinant human IGF-1 with an FDA label and a subcutaneous route, used in severe primary IGF-1 deficiency - Petriczko and colleagues reported on it in 2019 and Denaite and colleagues in Frontiers in Pediatrics in 2024. That is a real approval with real clinical evidence. It covers the native seventy-residue hormone. LR3 is an eighty-three-residue engineered analogue whose defining feature is deliberately altered binding behaviour, holds no marketing authorisation anywhere, and has essentially no primary literature under its own name - searches for IGF-1 LR3 and Long R3 IGF-1 return nothing. A nearby approval invites the inference that the analogue is somehow covered by it, and that inference is the most consequential error available in this category. Separately and unconditionally: IGF-1 and its analogues sit in WADA class S2, prohibited at all times, with the list extending to related substances and mimetics precisely so that structural modification creates no exemption.

Research applications

▸Cell culture supplementation where secreted IGFBPs confound dosing
▸IGF binding protein interaction and affinity studies
▸Recombinant protein expression and purification methodology
▸Disulfide folding and oxidative refolding research
▸Comparative work on engineered versus native growth factors
▸Anti-doping analytical method development

Handling checklist

✓Expect no PubChem record - proteins are indexed in UniProt (native IGF-1 is P05019)
✓Read the certificate for host cell protein, host DNA and endotoxin, not deletion sequences
✓Understand that mass spectrometry cannot detect a misfolded disulfide isomer
✓Treat loss of fold as the principal failure mode - it leaves mass unchanged
✓Avoid shaking and foaming; interfaces unfold proteins and aggregation is irreversible
✓Use low-binding consumables; adsorption is significant at microgram quantities
✓Aliquot before freezing - freeze-thaw is worse for a folded protein than a short peptide

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Reading mecasermin's approval as covering IGF-1 LR3

Fix: Increlex is native 70-residue rhIGF-1. LR3 is an 83-residue engineered analogue with altered binding, unlicensed everywhere. The approval does not transfer.

✗ Expecting a synthetic-peptide certificate for a recombinant protein

Fix: There are no deletion sequences here. The relevant tests are host cell protein, host DNA, endotoxin and something addressing conformation.

✗ Treating a clean mass spectrum as proof the protein is intact

Fix: A misfolded disulfide isomer has identical mass and composition. Only an activity or conformational assay addresses folding.

✗ Assuming absence from PubChem is a red flag

Fix: It is expected for a protein of this size - PubChem indexes small molecules, UniProt indexes proteins. This is unlike retatrutide, where absence is genuinely odd.

✗ Reading the cell-culture rationale as transferable

Fix: Bypassing IGFBP regulation is useful in a dish, where it is an experimental nuisance. In an organism the same system regulates a growth factor acting on nearly every tissue.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

Is there an approved IGF-1 medicine?: Yes — mecasermin, marketed as Increlex, is recombinant human IGF-1 administered subcutaneously. It is native rhIGF-1, not LR3.
Does that approval cover LR3?: No. LR3 is a different molecule with different binding behaviour and holds no marketing authorisation anywhere.
Why wasn't LR3 developed clinically?: Its modifications bypass a regulatory system rather than an obstacle. Its development context was cell culture, where systemic regulation is not a consideration.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

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