Modified insulin-like growth factor-1 with extended half-life (20+ hours). Researched for muscle growth, recovery, and cell proliferation.
Last Updated: May 2026
IGF-1 LR3 (Long R3 IGF-1) is a modified version of human insulin-like growth factor-1 with an arginine substitution at position 3 and an additional 13-amino-acid N-terminal extension. These modifications reduce IGFBP binding and extend half-life to approximately 20–30 hours, compared to ~10 minutes for native IGF-1. IGF-1 LR3 is not approved for any medical indication and is sold as a research-use-only compound by third-party laboratories. The compound is a downstream peptide that bypasses the pituitary GH axis entirely.
IGF-1 LR3 is a synthetic analog of human IGF-1 with two structural modifications: an arginine substitution replacing glutamate at position 3 (reducing IGFBP-3 binding affinity), and a 13-amino-acid N-terminal extension (further reducing IGFBP binding and extending circulation time). The result is a peptide that directly activates IGF-1 receptors throughout the body with substantially longer half-life than native IGF-1 — approximately 20–30 hours versus ~10 minutes. Unlike GHRH analogs and GHRPs, IGF-1 LR3 bypasses the pituitary axis entirely. Evidence level: Preclinical extensive (cell culture, rodent muscle and metabolic models); limited human clinical data.
Preclinical studies have demonstrated robust effects on muscle protein synthesis, satellite cell activation, glucose uptake, and tissue proliferation in cell culture and rodent models. Published human clinical trial data is sparse — IGF-1 LR3 has been studied as a research reagent more than as a therapeutic candidate. Native IGF-1 (mecasermin, Increlex) is FDA-approved for severe primary IGF-1 deficiency, but IGF-1 LR3 itself is not. Evidence level: Preclinical extensive; native IGF-1 (mecasermin) FDA-approved for primary IGFD; IGF-1 LR3-specific human data limited.
IGF-1 LR3 acts downstream of the GH axis — it directly activates IGF-1 receptors without requiring pituitary stimulation, unlike GHRH analogs (which work upstream at the GHRH receptor) and GHRPs (which work at the ghrelin receptor). This means IGF-1 LR3's effects are not subject to feedback regulation through the pituitary axis, and IGF-1 elevation is direct rather than mediated by endogenous GH pulses.
| Compound class | Site of action | Endogenous regulation | Half-life |
|---|---|---|---|
| GHRH analogs (sermorelin, tesamorelin) | Pituitary GHRH receptor | Pulsatile, feedback-regulated | Min to days |
| GHRPs (ipamorelin, GHRP-2) | Pituitary GHS-R1a | Pulsatile | ~1 hour |
| IGF-1 LR3 | Peripheral IGF-1R (direct) | No pituitary feedback | ~20–30 hours |
| IGF-1 DES | Peripheral IGF-1R (local) | No pituitary feedback | Short |
Direct IGF-1 receptor activation can produce hypoglycemia (IGF-1R has structural similarity to insulin receptors), particularly at higher doses or in fasted states. Sustained IGF-1 elevation raises theoretical concerns about cancer risk through the IGF-1 axis's role in cell proliferation, though IGF-1 LR3-specific long-term human data is absent. Injection-site reactions, transient headache, and mild lethargy are reported in community research use. Evidence level: Theoretical (IGF-1 axis biology); native IGF-1 (mecasermin) clinical safety data; IGF-1 LR3-specific long-term data unestablished.
IGF-1 LR3 is not approved for any medical indication anywhere in the world as of May 2026. Native IGF-1 (mecasermin, Increlex) is FDA-approved for severe primary IGF-1 deficiency, but the modified LR3 analog has no approval. IGF-1 LR3 is sold strictly as a research-use-only compound by third-party laboratories. Regulatory context in are peptides legal regulatory status by country.
IGF-1 LR3 is a 83-amino-acid recombinant or chemically synthesized peptide — substantially larger than most GH-axis peptides — making synthesis quality control more variable across vendors. Misfolded or truncated products may have altered activity. Independent HPLC purity testing and mass spectrometry identity confirmation (expected MW ~9,111 Da) are essential. The size also makes endotoxin testing particularly important. Guidance in how-to-test-peptides hub.
Peptigrity purchases IGF-1 LR3 vials anonymously at standard customer pricing, sends them to ISO-accredited third-party labs for HPLC, mass spectrometry, and endotoxin analysis, and publishes the unedited certificate of analysis. The lab test table above this section shows the cross-shop dataset. Methodology in how we calculate trust scores.
No. IGF-1 LR3 has two structural modifications relative to native IGF-1 — an arginine substitution at position 3 and a 13-amino-acid N-terminal extension — that reduce IGFBP binding and extend half-life from minutes to 20–30 hours. Native IGF-1 is FDA-approved as mecasermin (Increlex) for severe primary IGF-1 deficiency; IGF-1 LR3 is not approved.
IGF-1 LR3 has extended half-life (20–30 hours, systemic effects); IGF-1 DES is a truncated variant with very short half-life and primarily local anabolic activity at the injection site. They are used for different research applications — LR3 for systemic IGF-1R activation, DES for local muscle research.
IGF-1 LR3 is legal to purchase as a research chemical for laboratory use in most jurisdictions, but it is not approved for human consumption. Country breakdown in peptide legal status guide.
Sustained IGF-1 elevation through any mechanism raises theoretical cancer concerns because the IGF-1 axis is implicated in cell proliferation pathways. IGF-1 LR3-specific long-term human data is absent. Native IGF-1 (mecasermin) carries warnings about potential malignancy risk in its prescribing information. Anyone considering use should consult a licensed physician about the underlying axis biology.
Yes. IGF-1 and analogs are on the WADA Prohibited List (Section S2 — Peptide Hormones). Detection methods have improved. For drug-testing context, see do peptides show up on drug tests.
Independent third-party HPLC certificate of analysis from a lab the vendor does not own or pay, with mass spectrometry identity confirmation (expected MW ~9,111 Da) and endotoxin testing. The peptide's size makes purity and endotoxin verification particularly critical. COA interpretation in red flags in peptide certificates of analysis.
No. IGF-1 LR3 is not approved for human consumption and Peptigrity is an independent review platform, not a medical authority. Research-use dosing in community protocols varies, with hypoglycemia risk requiring particular caution. Anyone considering use should consult a licensed physician.
This section is for educational and informational purposes only and does not constitute medical advice. IGF-1 LR3 is not approved by the FDA or any other regulator for human use. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.
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