Section 01
What it's used for
Muscle Growth and Size
IGF-1 LR3 is the most studied lab-made version of IGF-1 for growing skeletal muscle. Research shows it increases both muscle cell size and the number of muscle cells, producing dose-dependent increases in lean body mass and muscle area.
▸Clinical wording
IGF-1 LR3 is the most extensively researched IGF-1 analog for skeletal muscle growth. It promotes both hypertrophy (increased cell size through protein synthesis) and hyperplasia (increased myonuclei through satellite cell activation). Research demonstrates dose-dependent increases in lean body mass and muscle cross-sectional area.
Lab Cell Culture Use
IGF-1 LR3 is mainly used in labs as a cell-culture additive, replacing serum for growing mammalian cells. It binds less to carrier proteins than natural IGF-1, making it more effective for cell growth. This is its main commercial use today.
▸Clinical wording
IGF-1 LR3 is widely used as a cell culture supplement, replacing serum in media for mammalian cell growth. Its reduced IGFBP binding makes it more effective than native IGF-1 for supporting cell proliferation in vitro. This is its primary commercial application.
Muscle Wasting Research
In research on age-related muscle loss (sarcopenia) and disease-related muscle wasting, IGF-1 LR3 appears to counter muscle loss by activating the mTOR protein-building pathway and muscle repair (satellite) cells.
▸Clinical wording
Research in age-related sarcopenia and disease-related muscle wasting demonstrates IGF-1 LR3 can counteract muscle atrophy through mTOR-mediated protein synthesis and satellite cell activation.
Injury and Tissue Repair
IGF-1 signaling is studied for repairing muscle, tendon, and ligament injuries. It works by boosting protein building, cell growth, and production of the extracellular matrix, the structural material that supports tissue.
▸Clinical wording
IGF-1 signaling promotes tissue repair in muscle, tendon, and ligament injuries through enhanced protein synthesis, cell proliferation, and extracellular matrix production.
Bone Growth and Density
IGF-1 is essential for building and maintaining bone. Research with IGF-1 LR3 shows increased growth of bone-building cells (osteoblasts) and more bone formation, with possible uses in osteoporosis and fracture healing.
▸Clinical wording
IGF-1 is essential for bone development and maintenance. Research with IGF-1 LR3 demonstrates enhanced osteoblast proliferation and bone formation, with potential applications in osteoporosis and fracture healing.
Metabolism Research
IGF-1 LR3 is used in laboratory research to study insulin-like effects on metabolism, including how cells take up glucose and how growth-factor and metabolic signaling pathways interact together in both health and disease.
▸Clinical wording
IGF-1 LR3 is used to study insulin-like metabolic signaling, glucose uptake, and the interplay between growth factor and metabolic pathways in health and disease.
Section 02
Mechanism of Action
Switching on the growth receptor
- It binds the IGF-1 receptor, a four-part switch sitting in the cell membrane.
- Binding makes the receptor tag itself and recruit adaptor proteins inside the cell.
- Two cascades follow: one for survival and metabolism, one for cell multiplication.
▸Clinical wording
IGF-1 Receptor Activation
IGF-1 LR3 binds to the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase heterotetrameric receptor (α2β2). Ligand binding activates the intrinsic tyrosine kinase of the β-subunits, triggering autophosphorylation and recruitment of insulin receptor substrate (IRS) proteins. This initiates two major downstream signaling cascades: PI3K/Akt/mTOR (metabolic/survival) and Ras/MAPK (proliferative).
Escaping the proteins that hold it
- Over 99 percent of natural IGF-1 is bound to six carrier proteins that limit its activity.
- This modified version binds those carriers far less and circulates mostly free.
- At the receptor it is reported as two to three times more potent than natural IGF-1.
▸Clinical wording
Enhanced Bioavailability
The key pharmacological advantage of IGF-1 LR3 over native IGF-1 is its greatly reduced binding to the six IGF-binding proteins (IGFBPs 1-6). Normally, >99% of circulating IGF-1 is bound to IGFBPs, which limit its bioactivity. IGF-1 LR3 circulates predominantly in free form, providing 2-3 times the potency of native IGF-1 at the receptor level.
Turning up the protein factory
- The survival cascade activates a master growth switch called mTOR inside the cell.
- That switch releases the cell's protein-making machinery by acting on two control proteins.
- Raised protein production is described as the main driver of this peptide's muscle-building action.
▸Clinical wording
mTOR-Mediated Protein Synthesis
Through the PI3K/Akt/mTOR pathway, IGF-1 LR3 activates the mechanistic target of rapamycin (mTOR), which phosphorylates p70S6K and 4E-BP1. This dramatically enhances ribosomal protein synthesis, driving muscle protein accretion and cell growth. mTOR activation is the primary mechanism of IGF-1 LR3's anabolic effects.
Waking muscle's own repair cells
- It activates satellite cells, the stem cells sitting alongside skeletal muscle fibres.
- Those cells multiply, mature and fuse into existing fibres, adding new nuclei.
- Adding nuclei differs from simply enlarging fibres, the usual route for anabolic agents.
▸Clinical wording
Satellite Cell Activation
IGF-1 LR3 activates skeletal muscle satellite cells (muscle stem cells), promoting their proliferation, differentiation, and fusion with existing myofibers. This hyperplastic growth mechanism (increasing the number of myonuclei) distinguishes IGF-1 from other anabolic agents that primarily produce hypertrophic growth.
Keeping cells from self-destructing
- The activated survival enzyme switches off three proteins that would trigger cell death.
- Blocking that death programme is described as contributing to tissue protection and regeneration.
▸Clinical wording
Anti-Apoptotic Signaling
Akt activation by IGF-1 LR3 phosphorylates and inactivates pro-apoptotic proteins (Bad, caspase-9, FKHR), promoting cell survival. This anti-apoptotic effect contributes to tissue protection and regeneration.
Section 03
Biological Pathways
- PI3K/Akt/mTOR Anabolic PathwayIGF-1R→IRS-1→PI3K→Akt→mTORC1→p70S6K/4E-BP1 is the master anabolic cascade, enhancing protein synthesis via S6 kinase and eIF4E while suppressing degradation via autophagy/FOXO inhibition.
- Ras/Raf/MEK/ERK Proliferation PathwayIGF-1R→Shc→Grb2→SOS→Ras→Raf→MEK→ERK1/2 drives cell proliferation, differentiation, and gene expression, and is critical for satellite cell proliferation and IGF-1's mitogenic effects.
- FOXO Protein Degradation InhibitionAkt phosphorylates FOXO1/FOXO3, excluding them from the nucleus and blocking transcription of atrophy genes MuRF1 and atrogin-1/MAFbx, reducing muscle protein breakdown.
- GSK-3β/Glycogen SynthesisAkt phosphorylates and inactivates GSK-3β, relieving inhibition of glycogen synthase and promoting glycogen storage in muscle and liver.
Section 04
Dosage Information
MFPAMPLSSL FVNGPRTLCG AELVDALQFV CGDRGFYFNK PTGYGSSSRR APQTGIVDEC CFRSCDLRRL EMYCAPLKPA KSA| Route / system | Context | Range studied | Limitation |
|---|---|---|---|
| Subcutaneous — mecasermin (rhIGF-1) | FDA label, severe IGF-1 deficiency in children | 0.04–0.08 mg/kg twice a day to start, up to 0.12 mg/kg twice a day — 2.8–8.4 mg per dose at 70 kg, each within ±20 min of a meal | Mecasermin is native IGF-1, not LR3, and it treats growth failure in children whose blood sugar is watched. The label warns of seizures from low blood sugar. |
| Intravenous — animal infusion | Rat and guinea pig growth models — the only LR3 dosing | Rats: 2.5 mg/kg a day infused for 3 days. Guinea pigs: 120 µg a day for 7 days — about 340 µg/kg a day at 350 g body weight | A pump running around the clock in a rodent, not a daily injection. Nobody converted these into a human dose, and what grew was gut and organs, not muscle. |
| Subcutaneous — self-administration | Circulating practice; no human study of LR3 | 20–100 µg per day, most often 40–50 µg, in 4–6 week cycles — roughly 0.2–1.4 µg/kg a day for a 70–90 kg adult | Circulating practice, not a finding. It carries mecasermin's low-blood-sugar risk without the meal rule, and at a 20–30 hour half-life doses overlap. |
| Intramuscular — into the trained muscle | Practice claim of growth at the injection site | The same 20–100 µg per day, put into the muscle just trained or split morning and evening; no separate amount is named | Growth at the injection site has never been tested for LR3 in a person. It binds carrier proteins weakly and lasts 20–30 hours, so it acts body-wide. |
Results
Syringe Fill Level (100u syringe)
Set positive values for: Recommended dose per kg.
Research Use Only. This information is for educational and research purposes only. Not intended for medical advice or self-medication.
Section 05
Protocols
- Protocol 01
IGF-1 LR3 Muscle Growth Protocol
Potent muscle building protocol using extended half-life IGF-1. For experienced users only.
- Focus
- Sport & Performance
- Level
- Advanced
- Duration
- 4–6 weeks
- Protocol 02
IGF-1 LR3 + PEG-MGF Advanced Stack
Maximum muscle growth stack combining systemic IGF-1 with localized MGF for hypertrophy and repair.
- Focus
- Sport & Performance
- Level
- Advanced
- Duration
- 6–8 weeks
Section 06
Stability & Storage
Lyophilised powder
IGF-1 LR3 is more prone to degradation than smaller peptides. Kept at −20 °C or below for long-term stability (12–18 months); at 2–8 °C, the lyophilised powder only stays stable for about 1–3 months.
After reconstitution
Dissolved in 0.1M acetic acid or sterile water with 0.1% BSA rather than bacteriostatic water, whose benzyl alcohol can trigger protein aggregation, and mixed with gentle swirling rather than vortexing or shaking it. The solution is kept at 2–8 °C, used within 14–21 days, and not put through repeated freeze-thaw cycles.
Section 07
Side Effects & Precautions
IGF-1 LR3's side effects follow from its strong, sustained activation of IGF-1 and insulin receptors: swings in blood sugar, tissue and organ growth, and a cancer-risk concern shared with the body's own growth signaling.
Blood sugar effects in both directions
- At high concentrations, IGF-1 LR3 activates the insulin receptor and boosts glucose uptake via IGF-1R/Akt/GLUT4 signaling.
- This can cause significant low blood sugar (hypoglycemia), especially combined with insulin or during fasting.
- Symptoms of low blood sugar include shakiness, sweating, confusion, and, in severe cases, loss of consciousness.
- With chronic high-dose use, this can paradoxically flip into insulin resistance through cross-desensitization of the IGF-1 and insulin receptors.
Organ and bone growth
- Chronic high-dose use can enlarge organs — including the intestines, spleen, and heart — an effect that is dose-dependent and more concerning with prolonged use.
- Prolonged high IGF-1 exposure can cause acromegaly-like features: growth of the jaw, hands, and feet from bone growth and soft-tissue expansion.
Joint pain and fluid retention
- GH/IGF-1-mediated effects on connective tissue can cause joint pain (arthralgia); combined with tissue growth effects, it is commonly reported.
- IGF-1 promotes sodium retention by the kidneys, causing fluid buildup in the extremities and face.
Tumor growth concern
IGF-1 signaling promotes cell proliferation and blocks programmed cell death (apoptosis) — the pathways cancer cells use. Elevated IGF-1 levels are epidemiologically linked to higher risk of breast, prostate, and colon cancer; use is contraindicated in people with known or suspected malignancies.
Section 08
Regulatory Status
WADA treats it as a banned growth factor regardless.
FDA / United States
Not approved for any human use
No regulator has approved IGF-1 LR3 itself for human therapeutic use. The only FDA-approved IGF-1 product is mecasermin (Increlex), a different, unmodified molecule approved solely for severe primary IGF-1 deficiency in children — an approval that does not extend to IGF-1 LR3.
Marketed use
Sold only as a research reagent
Biotechnology suppliers sell IGF-1 LR3 as a laboratory reagent and cell-culture supplement, explicitly not for human consumption. Products sold this way carry none of the purity, dosing, or manufacturing oversight a therapeutic approval would require.
WADA
Prohibited under category S2
WADA bans IGF-1 and all of its analogs, IGF-1 LR3 included, under S2.2 of the Prohibited List — Peptide Hormones, Growth Factors, Related Substances and Mimetics — at all times, in and out of competition, with no exemption for an unapproved product.
The «research use only» label on IGF-1 LR3 products does not turn them into approved medicines and says nothing about their purity or origin. Regulatory status differs between jurisdictions and changes over time; check the current documents of your own regulator before relying on any of this.
Section 09
Research Studies
- [1]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 potencyFrancis GL, Ross M, Ballard FJ, et al. · Journal of Molecular Endocrinology · 1992
- [2]Superior potency of infused IGF-I analogues which bind poorly to IGF-binding proteins is maintained when administered by injectionTomas FM, Lemmey AB, Read LC, et al. · Journal of Endocrinology · 1996
- [3]Molecular and Cellular Aspects of the Insulin-Like Growth Factor I ReceptorLeRoith D, Werner H, Beitner-Johnson D, et al. · Endocrine Reviews · 1995
- [4]Cellular Actions of the Insulin-Like Growth Factor Binding ProteinsFirth SM, Baxter RC · Endocrine Reviews · 2002
- [5]Mediation of IGF-1-induced skeletal myotube hypertrophy by PI(3)K/Akt/mTOR and PI(3)K/Akt/GSK3 pathwaysRommel C, Bodine SC, Clarke BA, et al. · Nature Cell Biology · 2001
- [6]Regulation of skeletal muscle growth by the IGF1-Akt/PKB pathway: insights from genetic modelsSchiaffino S, Mammucari C · Skeletal Muscle · 2011
- [7]Localized Igf-1 transgene expression sustains hypertrophy and regeneration in senescent skeletal muscleMusarò A, McCullagh K, Paul A, et al. · Nature Genetics · 2001
- [8]Satellite cell proliferation and skeletal muscle hypertrophyAdams GR · Applied Physiology, Nutrition, and Metabolism · 2006
- [9]IGF-I restores satellite cell proliferative potential in immobilized old skeletal muscleChakravarthy MV, Davis BS, Booth FW · Journal of Applied Physiology · 2000
- [10]Multiple Signaling Pathways of the Insulin-Like Growth Factor 1 Receptor in Protection from ApoptosisPeruzzi F, Prisco M, Dews M, et al. · Molecular and Cellular Biology · 1999
Section 10
Frequently Asked Questions
No human trial has tested IGF-1 LR3 for muscle growth — the compound was developed, and is still mainly used, as a cell-culture supplement to keep cells growing in the lab. The mechanistic case (activating IGF-1 receptors, driving mTOR-mediated protein synthesis and satellite-cell activation) is solid in isolated cells, and the only whole-animal dosing is rat and guinea-pig infusion studies that grew gut and organs, not muscle. What circulates as evidence for physique use is extrapolation from that biology, not a measured outcome in a person.
This is a real epidemiological concern rather than a settled one. IGF-1 signalling promotes cell proliferation and blocks programmed cell death — the same pathways cancer cells exploit — and elevated circulating IGF-1 is associated with increased risk of breast, prostate and colon cancer in observational studies. On that basis, use by anyone with a known or suspected malignancy is considered contraindicated, though no study has directly measured cancer incidence from IGF-1 LR3 use specifically.
The only FDA-approved human dosing in this family is for mecasermin (Increlex), which is native IGF-1, not LR3, given to children with severe IGF-1 deficiency at 0.04–0.12 mg/kg twice daily around meals to manage the seizure risk from low blood sugar. IGF-1 LR3 itself has no human dosing study at all — the 20–100 µg a day figure circulating in practice is self-reported use, not a research finding, and it carries mecasermin's hypoglycemia risk without the meal-timing rule that manages it.
IGF-1 LR3 has no FDA or other regulatory approval for human use anywhere; it is sold and classified as a research reagent and cell-culture supplement. WADA prohibits IGF-1 and all its analogues, including LR3, under category S2, banned both in and out of competition.
The most significant documented risk is hypoglycemia: at the concentrations reached with LR3, the peptide activates the insulin receptor directly and drives glucose uptake through IGF-1R/Akt/GLUT4 signalling, an effect that intensifies when combined with insulin or during fasting. Chronic high-dose use is also linked to organ enlargement (intestinal, splenic, cardiac hypertrophy), joint pain and, with prolonged exposure, acromegaly-like growth of the jaw, hands and feet.
IGF-1 LR3 degrades faster than smaller peptides: as lyophilised powder it holds up 12–18 months at −20 °C, but only about 1–3 months at 2–8 °C. It is reconstituted with 0.1M acetic acid or sterile water with 0.1% BSA rather than bacteriostatic water, whose benzyl alcohol can make the protein clump, mixed by gentle swirling, and used within 14–21 days without repeated freeze-thaw cycles.
This claim, about injecting into a just-trained muscle for localized growth, has never been tested for LR3 in a person. The peptide binds carrier proteins only weakly and has a 20–30 hour half-life, so pharmacologically it circulates and acts throughout the body rather than staying at the injection site.