--- title: "IGF-1 LR3 | PepTracker Pro" url: https://peptrackerpro.com/peptides/igf-1-lr3 description: "A modified form of IGF-1 with extended half-life, studied for muscle growth and tissue development." lang: en --- Skip to main content **Educational information only.** This site does not provide medical advice. Read full disclaimer (https://peptrackerpro.com/disclaimer) **Research-only content.** This page is for educational purposes and does not constitute medical advice. Read full disclaimer → (https://peptrackerpro.com/research-disclaimer) # IGF-1 LR3 Medium Evidence A modified form of IGF-1 with extended half-life, studied for muscle growth and tissue development. Aliases Long R3 IGF-1 +1 more Evidence Medium Evidence Last Updated 2026-05-27 Reading Time 2 min ## What It Is IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a synthetic 83-amino acid analog of human IGF-1 with two key modifications: an arginine substitution at position 3 and a 13-amino acid N-terminal extension peptide. These modifications reduce binding affinity to IGF-binding proteins (IGFBPs), resulting in a longer biological half-life and greater bioavailability compared to native IGF-1. While endogenous IGF-1 circulates largely bound to IGFBP-3 and is tightly regulated, IGF-1 LR3 remains predominantly in its free, biologically active form. IGF-1 signals through the IGF-1 receptor (IGF-1R), activating the PI3K/AKT and MAPK/ERK pathways to promote cell proliferation, protein synthesis, and glucose uptake in skeletal muscle. In cell culture models, IGF-1 LR3 is approximately 2–3× more potent than native IGF-1 at stimulating cell proliferation due to its reduced IGFBP sequestration. The same enhanced potency raises safety concerns: prolonged, unregulated IGF-1R activation is associated with increased risk of cellular hyperproliferation, and epidemiological data links elevated circulating IGF-1 levels to higher risk of certain cancers (colorectal, prostate, breast). IGF-1 LR3 is classified as a prohibited substance by WADA and is not FDA-approved for any indication. Native IGF-1 (mecasermin/Increlex) is FDA-approved only for severe primary IGF-1 deficiency. Also known as: Long R3 IGF-1, Long Arginine IGF-1 ## Why Researchers Study It IGF-1 LR3 has a significantly longer half-life than native IGF-1 due to its reduced affinity for IGF-binding proteins. This makes it a preferred research tool for studying sustained IGF-1 receptor activation, muscle hypertrophy pathways, and satellite cell-mediated tissue repair in preclinical models. ## Proposed Mechanisms - Binds IGF-1 receptors with similar affinity to native IGF-1 but resists binding protein sequestration - Promotes satellite cell activation and myoblast proliferation - Stimulates protein synthesis through PI3K/Akt/mTOR signaling cascade - Extended half-life allows sustained anabolic signaling in muscle tissue ## Evidence Snapshot Medium Evidence Low Medium High ## Commonly Discussed Benefits Muscle Growth: https://peptrackerpro.com/benefits/muscle-growth Recovery: https://peptrackerpro.com/benefits/recovery Fat Loss: https://peptrackerpro.com/benefits/fat-loss Researching IGF-1 LR3? Track it, set reminders, and keep notes in the free app. Track in App (https://app.peptrackerpro.com/?add=igf-1-lr3) ## Safety & Cautions - Potent growth factor with theoretical cancer risk concerns - May cause hypoglycemia - Not selective — promotes growth in all tissues - Not FDA-approved; requires careful medical consideration ## Comparisons See how IGF-1 LR3 compares to related peptides: IGF-1 LR3 vs CJC-1295: https://peptrackerpro.com/compare/igf-1-lr3-vs-cjc-1295 IGF-1 LR3 vs IGF-DES: https://peptrackerpro.com/compare/igf-1-lr3-vs-igf-des IGF-1 LR3 vs Ipamorelin: https://peptrackerpro.com/compare/igf-1-lr3-vs-ipamorelin IGF-1 LR3 vs PEG-MGF: https://peptrackerpro.com/compare/igf-1-lr3-vs-peg-mgf IGF-1 LR3 vs Lonapegsomatropin: https://peptrackerpro.com/compare/igf-1-lr3-vs-lonapegsomatropin ## Calculator Tools Use our research tools to explore dosing and reconstitution data: Reconstitution Calculator: https://peptrackerpro.com/calculators ## Citations 1. [1] Francis GL. et al. — Insulin-like growth factors 1 and 2 in bovine colostrum. Biochem J. 1988 PubMed (https://pubmed.ncbi.nlm.nih.gov/) ### Keep researching in the app - Log IGF-1 LR3 to your private tracker - Set a dosing reminder - Compare it side-by-side with your stack Open PepTracker Pro Free: https://app.peptrackerpro.com/?add=igf-1-lr3 Browse more peptides: https://peptrackerpro.com/peptides ## Related Peptides ### CJC-1295 Medium Evidence A growth hormone releasing hormone analog studied for stimulating growth hormone secretion. Muscle Growth (https://peptrackerpro.com/benefits/muscle-growth)Fat Loss (https://peptrackerpro.com/benefits/fat-loss)Recovery (https://peptrackerpro.com/benefits/recovery)Sleep (https://peptrackerpro.com/benefits/sleep)+1 more View Details: https://peptrackerpro.com/peptides/cjc-1295 \+ Compare: https://peptrackerpro.com/compare?select=cjc-1295 Track in App: https://app.peptrackerpro.com/?add=cjc-1295 ### IGF-DES Low Evidence A truncated form of IGF-1 with high potency and rapid local activity at the site of administration. Muscle Growth: https://peptrackerpro.com/benefits/muscle-growth Recovery: https://peptrackerpro.com/benefits/recovery View Details: https://peptrackerpro.com/peptides/igf-des \+ Compare: https://peptrackerpro.com/compare?select=igf-des Track in App: https://app.peptrackerpro.com/?add=igf-des ### Ipamorelin Medium Evidence A selective growth hormone secretagogue studied for targeted GH release with fewer side effects than other GH peptides. View Details: https://peptrackerpro.com/peptides/ipamorelin \+ Compare: https://peptrackerpro.com/compare?select=ipamorelin Track in App: https://app.peptrackerpro.com/?add=ipamorelin ### PEG-MGF Low Evidence A PEGylated splice variant of IGF-1 studied for muscle repair and satellite cell activation, with an extended half-life compared to native MGF. Muscle Growth: https://peptrackerpro.com/benefits/muscle-growth Recovery: https://peptrackerpro.com/benefits/recovery Wound Healing: https://peptrackerpro.com/benefits/wound-healing View Details: https://peptrackerpro.com/peptides/peg-mgf \+ Compare: https://peptrackerpro.com/compare?select=peg-mgf Track in App: https://app.peptrackerpro.com/?add=peg-mgf ### Lonapegsomatropin High Evidence Lonapegsomatropin (brand name Skytrofa, developed as TransCon hGH by Ascendis Pharma) is a long-acting, once-weekly prodrug of human growth hormone (somatropin) approved to treat growth hormone deficiency (GHD). Unlike conventional recombinant growth hormone, which must be injected every day, lonapegsomatropin uses Ascendis's TransCon ("transient conjugation") technology to slowly release fully active, unmodified growth hormone from an inert carrier over the course of a week, so patients inject only once weekly. It is built from three parts - unmodified somatropin, a methoxypolyethylene glycol (mPEG) carrier that shields the hormone and extends its time in the body, and a TransCon linker that connects them and then self-cleaves at normal body pH and temperature to release native growth hormone at a controlled, predictable rate. The FDA first approved lonapegsomatropin in August 2021 for children one year and older with GHD (the pivotal Phase 3 heiGHt trial showed it was non-inferior and numerically superior to daily somatropin for annualized height velocity in treatment-naive children), and in July 2025 the FDA expanded approval to adults with GHD based on the Phase 3 foresiGHt trial, in which once-weekly TransCon hGH significantly reduced trunk fat and increased lean body mass versus placebo. It is administered subcutaneously with the SKYTROFA Auto-Injector using a single-dose, dual-chamber prefilled cartridge. Lonapegsomatropin is a regulated prescription medicine, not a supplement or research chemical, and shares the class safety profile of growth hormone therapy. endocrine: https://peptrackerpro.com/benefits/endocrine growth: https://peptrackerpro.com/benefits/growth Body Composition: https://peptrackerpro.com/benefits/body-composition metabolic: https://peptrackerpro.com/benefits/metabolic View Details: https://peptrackerpro.com/peptides/lonapegsomatropin \+ Compare: https://peptrackerpro.com/compare?select=lonapegsomatropin Track in App: https://app.peptrackerpro.com/?add=lonapegsomatropin ## Structured data ```json [ { "@context": "https://schema.org", "@type": "Organization", "name": "PepTracker Pro", "url": "https://peptrackerpro.com", "logo": "https://peptrackerpro.com/favicon.png", "description": "Evidence-based educational resource dedicated to improving peptide research literacy.", "contactPoint": { "@type": "ContactPoint", "email": "hello@peptrackerpro.com", "contactType": "customer support" }, "sameAs": [] }, { "@context": "https://schema.org", "@type": "MedicalWebPage", "name": "IGF-1 LR3", "description": "A modified form of IGF-1 with extended half-life, studied for muscle growth and tissue development.", "url": "https://peptrackerpro.com/peptides/igf-1-lr3", "lastReviewed": "2026-05-27", "reviewedBy": { "@type": "Organization", "name": "PepTracker Pro Research Team", "url": "https://peptrackerpro.com" }, "isPartOf": { "@type": "WebSite", "name": "PepTracker Pro", "url": "https://peptrackerpro.com" } }, { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://peptrackerpro.com" }, { "@type": "ListItem", "position": 2, "name": "Peptides", "item": "https://peptrackerpro.com/peptides" }, { "@type": "ListItem", "position": 3, "name": "IGF-1 LR3", "item": "https://peptrackerpro.com/peptides/igf-1-lr3" } ] }, { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "People researching IGF-1 pathway compounds?", "acceptedAnswer": { "@type": "Answer", "text": "IGF-1 LR3 is a research peptide studied in preclinical models. 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