Page data last changed: . Registry refreshes and identity assessments are separate from scientific content review.
An 83-residue engineered IGF-1 made for cell culture and fetal-sheep physiology — sold online as if it were a small peptide, with no human data at all.
Also known as: Long R3 IGF-1 · LR3 IGF-1 · IGF1 LR3 · Long-Arg3-IGF-1
Part of the Growth hormone & IGF peptides cluster
Overview
IGF-1 LR3 (Long R3 IGF-1) is a recombinant 83-amino-acid analogue of human insulin-like growth factor 1, engineered for use as a laboratory growth factor and studied in fetal-sheep physiology. It activates the IGF-1 receptor to drive cell proliferation, and in cultured fetal cardiomyocytes it increased DNA synthesis three- to five-fold. It has no human trials, no approval, and a 2025 sheep study found it did not promote growth in growth-restricted fetuses. It is sold unapproved online and is prohibited in sport.
Source & context
Biological / chemical source: Recombinant / synthetic analog
Primary research or clinical context: Research compound — a laboratory growth factor with no approval and no human trials; sold unapproved and prohibited in sport
What IGF-1 LR3 is
IGF-1 LR3 is an engineered version of human insulin-like growth factor 1, the 70-residue hormone through which growth hormone exerts most of its growth-promoting effects. The LR3 form is 83 residues long and is manufactured recombinantly — including as a fusion protein expressed in the yeast Pichia pastoris (Lu et al., Applied Microbiology and Biotechnology 2023) — for use as a cell-culture growth factor and in animal physiology experiments. At 83 amino acids it is a small protein rather than a peptide, and it is far more potent as a proliferation signal than any secretagogue on this site because it acts at the growth-factor receptor directly rather than through the pituitary.
Mechanism
IGF-1 LR3 activates the IGF-1 receptor, a receptor tyrosine kinase. In cultured fetal sheep cardiomyocytes it increased bromodeoxyuridine uptake — a marker of DNA synthesis and proliferation — three- to five-fold, and blocking either the ERK or the PI3K pathway abolished the effect (Sundgren et al., American Journal of Physiology 2003). The IGF-1 receptor's signalling depends on its glycosylation state; CHO cells with defective N-glycosylation showed reduced IGF-1R levels and altered signalling (Salvi et al., International Journal of Molecular Sciences 2022). These are cell-biology findings about a growth factor, not evidence about a supplement.
What the animal studies show — including the negative one
The largest body of work is in fetal sheep, where LR3 IGF-1 is infused to study growth. A one-week infusion increased fetal organ growth but not by stimulating nutrient transfer (Stremming et al., American Journal of Physiology 2021) and, in the same model, reduced glucose-stimulated insulin secretion through an intrinsic islet defect (White et al., 2021), an effect that did not persist in isolated islets after acute infusion (White et al., 2023). Cardiac growth stimulated by IGF-1 was matched by coronary vascular growth (Jonker et al., FASEB Journal 2020). Most tellingly, in late-gestation growth-restricted fetal sheep, one week of IGF-1 LR3 did not promote growth — body weight, insulin, glucose and insulin secretion were unchanged (White et al., American Journal of Physiology 2025). A 2025 materials study used controlled LR3 release in a nerve conduit for sciatic-nerve regeneration in rats (Yavuz et al., 2025).
| Study | Design | Finding |
|---|---|---|
| Sundgren 2003 | Cultured fetal cardiomyocytes; in-vivo LR3 | 3–5× BrdU uptake in culture; no hypertrophy in vivo |
| Stremming 2021 | 1-week IGF-1 infusion | Organ growth ↑ without increased nutrient transfer |
| White 2021 / 2023 | 1-week and acute infusions | Reduced glucose-stimulated insulin secretion (intrinsic islet defect) |
| White 2025 | 1-week LR3 in growth-restricted fetuses | No growth promotion; insulin and glucose unchanged |
Human evidence
There is none. ClinicalTrials.gov lists no study of IGF-1 LR3, and the pack's 11 PubMed records contain no human pharmacokinetics, safety or efficacy data. A 2026 review of performance-enhancing peptides that modulate the GH–IGF-1 axis discusses the gap between clinical evidence and patient self-administration for this class of agents (Dominikowski et al., Frontiers in Endocrinology 2026). Everything said online about IGF-1 LR3 in humans is extrapolated from its identity as a growth factor.
Why this one matters more than most
IGF-1 signalling drives proliferation in essentially every tissue, including tumours, and reduces insulin secretion in the sheep model. Unlike a secretagogue, which can only raise growth hormone as far as the pituitary allows, an exogenous growth factor bypasses that control entirely. The site's original one-line description — a high-risk, high-search growth factor often mislabelled as a simple peptide — remains the accurate summary. It is prohibited in sport as a growth factor.
Regulatory status
IGF-1 LR3 has no approval in any jurisdiction and no IUPHAR ligand record; its legitimate market is cell-culture reagents sold to laboratories. Products sold online for human use are unlicensed, of unverified identity and potency, and — because the molecule is a folded 83-residue protein — unusually easy to sell mis-folded or degraded, which a purity certificate does not detect. This profile is educational; it is not guidance on obtaining or using any product and it is not medical advice.
Structure & chemistry
Molecular identity & reference confidence
Reference mass unavailable
Reference values are taken from the cited molecular record or curated profile. A database match is not independent laboratory verification; modifications, counter-ions, and formulations can change the measured mass.
- Molecular form
- 83-residue engineered form of human IGF-1 (70 residues); produced recombinantly, including in Pichia pastoris fusion systems (Lu et al., 2023)
- Species
- Not established by this molecular identity audit
- Termini (N / C)
- Not specified / Not specified
Average reference mass
Reference policy updated: 2026-10-05
- Receptors
- Insulin-like growth factor 1 receptor (IGF-1R), a receptor tyrosine kinase signalling through ERK and PI3K (Sundgren et al., 2003; Salvi et al., 2022)
- Backbone
- 83-residue engineered form of human IGF-1 (70 residues); produced recombinantly, including in Pichia pastoris fusion systems (Lu et al., 2023)
- Status
- Research protein; no approval; no ClinicalTrials.gov entry; prohibited in sport as a growth factor
Chemistry values: curated profile.
Change log
Dated observations from the data pipeline (registry flags, trial footprints, identifiers) and editorial reviews of this profile.
- EditorialProfile content reviewed and updated by the editorial team.
FAQ about IGF-1 LR3
What is IGF-1 LR3?+
IGF-1 LR3 (Long R3 IGF-1) is a recombinant 83-amino-acid analogue of human insulin-like growth factor 1, engineered for use as a laboratory growth factor and studied in fetal-sheep physiology. It activates the IGF-1 receptor to drive cell proliferation, and in cultured fetal cardiomyocytes it increased DNA synthesis three- to five-fold. It has no human trials, no approval, and a 2025 sheep study found it did not promote growth in growth-restricted fetuses. It is sold unapproved online and is prohibited in sport.
What Canadian product status is recorded for IGF-1 LR3?+
Canadian product status for IGF-1 LR3 has not been verified in this profile. No verified record here does not mean no authorization exists. Status depends on the product, formulation and use; consult Health Canada's product records.
What is the typical length of IGF-1 LR3?+
IGF-1 LR3 is commonly described as approximately 83 amino acids (Modified insulin-like growth factor 1 (research protein)).
What is IGF-1 LR3?+
An engineered 83-residue recombinant form of insulin-like growth factor 1, made as a cell-culture growth factor and used in fetal-sheep physiology research. It activates the IGF-1 receptor.
Is IGF-1 LR3 a peptide?+
At 83 amino acids it is a small protein, not a short peptide. It is often mislabelled as a peptide by sellers.
Has IGF-1 LR3 been tested in humans?+
No. There are no registered trials and no human safety or efficacy data.
Does IGF-1 LR3 build muscle?+
No human study exists. In growth-restricted fetal sheep a one-week infusion did not promote growth, and IGF-1 infusion reduced insulin secretion in that model.
What is IGF-1 LR3's half-life?+
The evidence pack does not report a human figure; there are no human pharmacokinetic studies.
Is IGF-1 LR3 approved or legal in sport?+
It is not approved anywhere and is prohibited in sport as a growth factor.
Further reading
- Hormone axisGH Secretagogue Peptides Explained: CJC-1295, Ipamorelin, GHRPsEducational overview of growth hormone secretagogue peptides—GHRH analogs vs GHRPs, DAC vs no DAC, receptors, and research context.
- Not a peptideIs MK-677 (Ibutamoren) a Peptide? No — It Is an Oral Small-Molecule Ghrelin Mimetic. What the Trials ShowedMK-677 (ibutamoren) is sold next to peptides and stacked with them, but it is a small synthetic molecule that activates the ghrelin receptor by mouth. This guide explains what it is, how it differs from GHRH and GHRP peptides, what its clinical trials showed — including the safety signal that stopped one — and its regulatory status.
- SafetyPeptide Safety and Risks: A Balanced Educational OverviewAn objective, balanced overview of what research does and does not establish about peptide risks—unknowns, purity and contamination concerns, and why unapproved compounds carry uncertainty. Not reassurance and not medical advice.
- FoundationsPeptides vs SARMs: A Science-Literacy ComparisonAn educational look at how peptides (amino-acid chains acting through receptor and signaling biology) differ from SARMs (non-peptide small molecules targeting the androgen receptor). Framed as science literacy, not usage advice.
- FoundationsWhat Are Research Peptides? A Clear Educational GuideLearn what “research peptides” means, how they differ from approved peptide drugs, quality markers (COA, purity), and how to study them responsibly.
Related peptides
References & further reading
- 1.White et al. (2025). IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep. Am J Physiol Endocrinol Metab
- 2.White et al. (2023). Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets. J Dev Orig Health Dis
- 3.Yavuz et al. (2025). Revolutionary decellularized Alstroemeria stem-based nerve conduit integrated with GelMA and controlled IGF-1 LR3 release for enhanced rat sciatic nerve regeneration. Int J Biol Macromol
- 4.Sundgren NC et al. (2003). Extracellular signal-regulated kinase and phosphoinositol-3 kinase mediate IGF-1 induced proliferation of fetal sheep cardiomyocytes. American Journal of Physiology
- 5.Jonker SS et al. (2020). Coronary vascular growth matches IGF-1-stimulated cardiac growth in fetal sheep. FASEB Journal
- 6.Stremming J et al. (2021). IGF-1 infusion to fetal sheep increases organ growth but not by stimulating nutrient transfer to the fetus. American Journal of Physiology
- 7.White A et al. (2021). Reduced glucose-stimulated insulin secretion following a 1-wk IGF-1 infusion in late gestation fetal sheep is due to an intrinsic islet defect. American Journal of Physiology
- 8.Lu Z et al. (2023). Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris. Applied Microbiology and Biotechnology
- 9.Dominikowski A et al. (2026). The emerging landscape of performance-enhancing peptides modulating the GH-IGF1 axis. Frontiers in Endocrinology