IGF-1 LR3

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Snapshot

Chemistry and make-up

IGF-1 LR3 is not a short synthetic peptide but a small recombinant protein of 83 amino acids (~9.1 kDa), an engineered analogue of native human IGF-1 (70 residues). Two deliberate modifications define it. First, an Arg-for-Glu swap at position 3 (Glu3Arg), the “R3” in the name. Second, a 13-residue N-terminal extension (a sequence attributed to the human proinsulin B chain), the “Long” in the name. Together these changes cut binding to the IGF binding proteins (IGFBPs) by roughly a thousandfold while preserving affinity for the IGF-1 receptor, so more of the molecule stays free and active and the functional half-life stretches from minutes (native IGF-1) to a reported ~20 to 30 hours [A/D]. Like native IGF-1 the fold is stabilised by intramolecular disulfide bonds, which is why the reported molecular formula carries multiple sulfur atoms; the correct disulfide pairing is part of the authentic, active structure and cannot be read off mass alone. Because it is expression-derived rather than SPPS-made, identity and correct folding (not just purity) are the QC questions, and the exact formula and mass should be taken from the batch CoA and PubChem rather than assumed.

What it is studied for (evidence)

• Mechanism (well characterised for the IGF axis [A]): IGF-1 signalling through IGF1R drives the PI3K-Akt and MAPK pathways, promoting cell growth, proliferation, protein synthesis and survival across muscle and many other tissues. The LR3 modifications were engineered specifically to reduce IGFBP sequestration and prolong action, a design goal confirmed in the analogue literature [A].
• Established: LR3 IGF-1 is a long-standing laboratory and biomanufacturing reagent, widely used as a potent cell-culture growth supplement (for example in CHO and stem-cell culture) because its IGFBP resistance makes it more active than native IGF-1 in vitro [A/C]. That in-vitro use is genuinely established.
• Emerging / thin: human data for the physique, recovery or “growth” uses that vendors imply are essentially absent. There is no completed randomised controlled trial of IGF-1 LR3 for any body-composition or performance indication. Native IGF-1 (mecasermin) has a defined but narrow medical role (severe primary IGF-1 deficiency), which is a different, licensed molecule, not LR3.
• Marketing claims vs data: research-chemical and bodybuilding vendors sell LR3 as a muscle-growth and recovery agent with dosing charts. Those claims lean on cell-culture potency and on native-IGF-1 physiology, not on human LR3 trials, and IGF-1 receptor agonism carries theoretical proliferative and hypoglycaemic concerns that vendor copy tends to omit. Treat all human-use and dosing guidance as marketing.
• Human clinical status: no approved IGF-1 LR3 product anywhere. It exists as a research reagent and a grey-market physique peptide, not a medicine.

Handling, format and stability

Supplied lyophilised; reconstituted with bacteriostatic or sterile water for research handling (no dosing guidance here). As a folded, disulfide-containing protein it is sensitive to heat, oxidation (which can scramble disulfides), pH extremes and repeated freeze-thaw, so the lyophilised powder is stored cold and dark, and reconstituted material is treated as short-lived and cold-chain dependent. Some suppliers add a carrier protein for the pure research reagent grade; a grey-market physique vial usually will not, which matters for stability and identity.

Regulatory and trade status

• UK/EU RUO: research use only; not an approved medicine. Any muscle-growth, recovery or anti-ageing framing pushes a listing toward “medicinal product by presentation”, so keep listings strictly RUO with no performance claims.
• US: no approved IGF-1 LR3 drug. Note native IGF-1 (mecasermin, Increlex) is an approved medicine for a narrow deficiency indication, so LR3 sits close to an approved active class, which raises the regulatory temperature versus a never-approved peptide.
• WADA (sport): prohibited. IGF-1 and its analogues/releasing factors are named under S2 (peptide hormones, growth factors, related substances and mimetics), “Growth factors and growth factor modulators”, prohibited at all times. IGF-1 LR3 falls squarely in this category [B — confirm current-year WADA wording].
• Customs / import: a known physique/growth agent, so higher enforcement interest than a benign repair peptide.

Sources

• [A] IGF-1 receptor signalling and IGF/IGFBP axis (review literature on PI3K-Akt/MAPK and IGFBP biology) — PubChem/NCBI IGF1 gene and pathway records — https://pubchem.ncbi.nlm.nih.gov/
• [A/C] Recombinant Long R3 IGF-I as a cell-culture growth supplement (IGFBP-resistant, more potent than native IGF-1 in vitro), R&D Systems datasheet — https://www.rndsystems.com/products/recombinant-human-lr3-igf-i-igf-1-gmp-protein-cf_8335d-gmp
• [B] WADA Prohibited List, S2 peptide hormones / growth factors (IGF-1 and analogues) — https://www.wada-ama.org/en/prohibited-list
• [C] ProSpec recombinant Long R3 IGF-1 (83-aa, ~9.1 kDa, Glu3Arg + 13-aa N-terminal extension) — https://prospecbio.com/products/long-r3-igf1-human
• [B/C] ChemicalBook CAS 946870-92-4 (IGF-1 LR3 identity, MW ~9111) — https://www.chemicalbook.com/ChemicalProductProperty_EN_CB6947862.htm
• [D] Vendor pages (Spartan Peptides, American Peptides, Anderson Longevity) — commercial; publish dosing and physique claims, which we do not use.

Plain summary

IGF-1 LR3 is a lab-engineered version of the growth factor IGF-1, an 83-amino-acid protein of about 9.1 kDa with two changes (an Arg-for-Glu swap at position 3 and a 13-amino-acid N-terminal extension) that let it dodge the IGF binding proteins and stay active far longer than natural IGF-1. Its genuinely established use is as a potent cell-culture growth reagent; the muscle-growth and recovery claims sold to physique buyers have no human trial support and it is WADA-prohibited as a growth factor. Commercially the trap is that it is a folded, disulfide-bonded protein, so a rigorous CoA needs MS identity near 9111 and folding-aware testing, not just a purity number, and every listing should stay strictly research use only.

For laboratory and research use only (RUO). Not for human or veterinary use, not for consumption, and not a medicine. Information is a research summary, not medical advice, and contains no dosing guidance.

For laboratory research use only. Not for human or veterinary use, not for consumption, and not a medicine. This is a research summary, not medical advice, and contains no dosing guidance.