Is IGF-1 LR3 an approved drug or for research use only?

IGF-1 LR3 (Long R3 IGF-1) is sold strictly for research use only (RUO). It is not an approved medicine in Canada, the United States or elsewhere, has not been through human clinical trials, and is not intended for human or veterinary use, diagnosis or treatment.

How does IGF-1 LR3 differ from native IGF-1?

It is an 83-residue analog of the 70-residue native IGF-1, with arginine substituted for glutamate at position 3 and a 13-amino-acid N-terminal extension (the source of the 'long' in its name). Researchers reported these changes lower its affinity for IGF-binding proteins, leaving a larger free fraction of ligand and greater in-vitro potency in IGFBP-containing systems.

What is the evidence base for IGF-1 LR3?

Published data are limited to in-vitro (cell-culture) and animal studies, graded here as C. There are no controlled human clinical trials. Animal findings differ by model — anabolic in some rat studies but growth-suppressing in pigs at the dose tested.

What is the half-life of IGF-1 LR3?

No controlled human pharmacokinetic data are established. Although it is often marketed as 'long-acting,' the peer-reviewed rat comparison cited here reported that LR3-IGF-I is actually cleared from the circulation faster than native IGF-1, because it largely escapes the long-lived IGF-binding-protein/acid-labile-subunit complex that protects native IGF-1; its potency advantage was attributed to a larger free fraction rather than to a longer half-life.

IGF-1 LR3 Dosage, Half-Life & Research

IGF-1 LR3 (Long R3 IGF-1) is a recombinant 83-residue analog of human insulin-like growth factor 1. It carries an arginine-for-glutamate substitution at position 3 and a 13-amino-acid N-terminal extension derived from methionyl porcine growth hormone, modifications first described by Francis and colleagues in 1992.¹ The “long” in its name refers to this N-terminal extension. These changes sharply lower its affinity for IGF-binding proteins (IGFBPs), which researchers reported leaves a larger free fraction of ligand available to receptors and gives it greater in-vitro potency than native IGF-1 in IGFBP-containing systems.¹² It is sold strictly for research use only (RUO); it is not an approved drug and the published evidence is limited to cell-culture and animal models.³ Because IGF-1 LR3 is sometimes grouped with GH-axis tools, note that it acts downstream of growth hormone at the IGF-1 receptor rather than as a GH secretagogue. Reported chemical identifiers vary slightly between vendor databases and PubChem does not publish a computed value for several of them, so figures below are stated as published or marked “Not established.”

Structure

Sequence & identity

MFPAMPLSSLFVNGPRTLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA · C₄₀₀H₆₂₅N₁₁₁O₁₁₅S₉ · ~9117.5 g/mol (as published; not PubChem-computed)

IGF-1 LR3 is a single-chain polypeptide of 83 residues cross-linked by three disulfide bonds, so it is not a simple linear peptide. PubChem (CID 381123731) lists no computed InChIKey or molecular descriptors for this entry.⁵

What the research shows

Mechanisms studied

Native IGF-1 circulates almost entirely bound to IGFBPs (chiefly IGFBP-3), which limits how much free ligand reaches tissue receptors. Francis and colleagues reported that the Arg3 substitution plus the hydrophobic N-terminal extension reduce IGF-1 LR3’s affinity for IGFBPs while preserving binding to the IGF-1 receptor.¹ Researchers observed that this leaves a larger free fraction available to activate the receptor, which they proposed as the basis for its greater potency in IGFBP-containing cell-culture assays — often cited as roughly two- to threefold over native IGF-1, though the original work also found the analog was less potent than native IGF-1 in cells that secrete no IGFBPs.¹² Notably, because it largely escapes the IGFBP/acid-labile-subunit reservoir that protects native IGF-1, Tomas and colleagues reported that LR3-IGF-I is actually cleared from the circulation more quickly than native IGF-1 in rats, yet retained superior potency even when injected.² In finisher pigs Dunaiski and colleagues reported that infused Long-[R3]-IGF-I suppressed plasma growth hormone, IGFBP-3 and endogenous IGF-1 and reduced weight gain — illustrating that observed effects depend heavily on the model and dose.³

Reported in studies

Dosing in the research literature

The figures below summarise regimens as reported in published research — they are not recommendations or directions for use.

Source / model	Regimen reported	Notes
Francis et al. 1992, J Mol Endocrinol (in-vitro)¹	Cell-culture potency assays; activity characterized in cultured cells rather than by a body-weight dose	Original characterization of Long-[Arg3]-IGF-I. In-vitro only; not a human regimen.
Tomas et al. 1996, J Endocrinol (rat)²	Long-R3-IGF-I administered to rats by infusion and by injection in comparative anabolic studies	Animal model. Researchers reported the IGFBP-poor-binding analog retained superior potency when injected despite faster clearance. Exact mg/kg values per the primary paper.
Dunaiski et al. 1997, J Endocrinol (pig)³	180 micrograms/kg/day Long-[R3]-IGF-I infused over 4 days in finisher pigs	Animal model. At this dose researchers observed reduced average daily gain, food intake, plasma GH (-23%), IGFBP-3 and endogenous IGF-1.

Research use only. Peptigo products are sold to qualified researchers for laboratory use. This information summarises published research for reference and is not medical advice, a dosing recommendation, or directions for human or animal use.

Reported in studies

Effects observed in research

In cell-culture work, researchers reported that IGF-1 LR3 binds the IGF-1 receptor and stimulates IGF-1-receptor signaling more effectively than native IGF-1 at matched concentrations in IGFBP-containing systems, attributing this to its poor IGFBP binding.¹² In rats, Tomas and colleagues observed anabolic responses (nitrogen retention and growth measures) to IGFBP-poor-binding IGF-1 analogs, and reported that LR3-IGF-I was cleared from the circulation faster than native IGF-1 yet kept its potency advantage when injected.² By contrast, in finisher pigs Dunaiski and colleagues reported that infused Long-[R3]-IGF-I decreased weight gain, food intake and circulating GH, IGFBP-3 and IGF-1, which they linked to feedback suppression of the GH axis.³ Laajoki and colleagues characterized the solution secondary structure of Long-[Arg3]-IGF-I by NMR, confirming an IGF-1-like fold.⁴ No controlled human efficacy or safety data are available, and the compound is not approved for human use.

Honest assessment

Strength of evidence

Grade C

Grade C — animal and in-vitro evidence only. The published record consists of cell-culture characterization, rodent anabolic studies, livestock infusion work and a structural (NMR) study.¹²³⁴ There are no controlled human clinical trials of IGF-1 LR3, and it has never been an approved human drug; IGF-1 and its analogs are also prohibited in sport. Reported animal findings are not consistent in direction (anabolic in some rat models, growth-suppressing in pigs), underscoring that effects are model- and dose-dependent. The popular description of IGF-1 LR3 as “long-acting” should be treated with caution: the only peer-reviewed pharmacokinetic comparison cited here found the analog is cleared faster than native IGF-1 because it escapes the long-lived IGFBP/ALS complex,² and no controlled human half-life data exist. Chemical identifiers should also be treated with caution: vendor databases disagree on the exact hydrogen count (e.g. C400H625 vs C400H619) and PubChem publishes no computed molecular weight or InChIKey for this entry,⁵ so the formula and mass above are reported “as published” rather than independently verified.

Handling

Reconstitution & storage

Reconstitute with bacteriostatic water for laboratory handling. Store lyophilised material frozen and reconstituted material refrigerated. Use Peptigo’s reconstitution calculator and storage cheat sheet for working figures.

References

Francis GL, Ross M, Ballard FJ, Milner SJ, Senn C, McNeil KA, Wallace JC, King R, Wells JR. 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. J Mol Endocrinol. 1992;8(3):213-223. PMID: 1378742. https://pubmed.ncbi.nlm.nih.gov/1378742/
Tomas FM, Lemmey AB, Read LC, Ballard FJ. Superior potency of infused IGF-I analogues which bind poorly to IGF-binding proteins is maintained when administered by injection. J Endocrinol. 1996;150(1):77-84. PMID: 8708565. doi:10.1677/joe.0.1500077. https://pubmed.ncbi.nlm.nih.gov/8708565/
Dunaiski V, Dunshea FR, Walton PE, Goddard C. Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs. J Endocrinol. 1997;155(3):559-565. PMID: 9488001. doi:10.1677/joe.0.1550559. https://pubmed.ncbi.nlm.nih.gov/9488001/
Laajoki LG, Le Breton E, Shooter GK, Wallace JC, Francis GL, Carver JA, Keniry MA. Secondary structure determination of 15N-labelled human Long-[Arg-3]-insulin-like growth factor 1 by multidimensional NMR spectroscopy. FEBS Lett. 1997;420(1):97-102. PMID: 9450557. doi:10.1016/S0014-5793(97)01496-8. https://pubmed.ncbi.nlm.nih.gov/9450557/
PubChem Compound Summary for CID 381123731, Long R3 IGF-1. National Library of Medicine. https://pubchem.ncbi.nlm.nih.gov/compound/381123731
ChemicalBook. LONG R3 IGF-I recombinant analog, CAS 143045-27-6. https://www.chemicalbook.com/ChemicalProductProperty_EN_CB3497058.htm

Written by the Peptigo Research Team · scientifically reviewed by Peter, Peptigo Research Team · Last reviewed June 2026. We cite primary literature and flag where evidence is limited. Our sourcing & RUO policy →