IGF-1 LR3
Also known as: Long-Arg3 IGF-1 · Receptor-grade IGF-1 LR3 · rhIGF-1 LR3
Phase 1/2 clinical research for short-stature contexts; documented hypoglycaemia risk; in vitro mitogenic activity on cancer cell lines reported; no regulatory approvals.
Rating per Panya's data-first method, not regulator endorsement. The mechanism, dose, and risk sections below carry the underlying data.
IGF-1 LR3 is a synthetic 83-amino-acid analogue of insulin-like growth factor 1 with the N-terminal extended by 13 residues and Glu3 substituted with Arg3. The modifications extend serum half-life from 10-20 minutes (native IGF-1) to 20-30 hours and reduce sequestration by IGF-binding proteins.
Last reviewed · Panya.health editorial
Panya scores vendors against an 11-signal rubric. Vendors at or above 70 out of 100 are routable; below 70 are documented but get no Panya affiliate link. For prescription peptides like Mounjaro and Wegovy, Panya routes today through licensed clinicians. For research peptides like IGF-1 LR3, vendor scorecards land in a follow-up sprint after legal review and payment processor selection. Until then, the page surfaces commonly-mentioned vendor names so adults can do their own diligence. We do not yet earn commission on any IGF-1 LR3 vendor.
Not medical advice. IGF-1 LR3 is not approved for human medical use in most jurisdictions. The data below is what users do; it is not what regulators have validated. You decide your risk profile.
What it does, and how
Native IGF-1 is the primary downstream effector of growth hormone signalling; it binds the IGF-1 receptor (IGF1R) on most tissues and drives mitogenic, anabolic, and metabolic effects. Roughly 99% of circulating native IGF-1 is bound to IGF-binding proteins (primarily IGFBP-3) at any moment, which limits free-fraction availability. The LR3 modification, developed by Francis et al. at the University of Adelaide in the 1990s, extends the N-terminus by 13 residues from porcine growth hormone and substitutes glutamate-3 with arginine-3; both changes reduce IGFBP affinity, increasing free fraction and effective serum half-life. Pharmacology: IGF-1 LR3 retains full IGF1R agonism, with reported potency 2 to 3 times native IGF-1 in cell-culture mitogenic assays (Francis 1992). The receptor it binds is widely expressed; downstream effects span muscle protein synthesis (via PI3K/Akt/mTOR), satellite-cell activation, glucose uptake, and lipolysis-suppression in adipose tissue.
Typical practice
Clinical research has used native rhIGF-1 (mecasermin, Increlex) in short-stature contexts at 40 to 120 µg/kg twice daily subcutaneous; LR3 has been studied in research contexts at 1 to 5 µg/kg per day. Community practice for off-label muscle-growth use runs 20 to 100 µg per day subcutaneous, in cycles of 2 to 6 weeks with breaks. Some users dose pre-workout based on the theory that local muscle uptake post-exercise increases anabolic signal; this is mechanistically plausible but not empirically validated for LR3 specifically. Reconstitution is typically a 1 mg vial in 1 to 5 mL bacteriostatic water; dilution volume sets the per-draw concentration. Stacking with HGH or with anabolic-steroid cycles is common in bodybuilder protocols; the AE profile compounds in those contexts. There is no regulator-validated dose for the muscle-growth use case; the doses above reflect community practice and the small LR3 research literature.
The dosing above is community practice, not a regulator-validated protocol. Trial-validated dosing for IGF-1 LR3 in humans does not exist for most use cases listed.
Risks and contraindications
Hypoglycaemia is the documented dose-limiting adverse event: IGF-1 LR3 is structurally close to insulin and activates IGF1R/insulin-receptor heterodimers, producing real glucose-lowering effects at therapeutic doses. Mecasermin (native IGF-1) trials reported hypoglycaemia in 30 to 50% of paediatric subjects depending on dose and protocol (Chernausek 2007); LR3's longer half-life concentrates the effect over longer windows. Joint pain, peripheral oedema, and parotid swelling have been reported in mecasermin trials. The mitogenic activity of IGF-1 on cancer cell lines is well-documented in vitro (Pollak 2008 review): IGF1R activation is proliferative on most epithelial cancer cell lines tested, and elevated circulating IGF-1 has been epidemiologically associated with several cancer types in observational cohorts; whether exogenous LR3 administration affects clinical cancer biology in adults is an open clinical question with no controlled trial evidence either direction. The longer half-life of LR3 vs. native IGF-1 also extends the cardiac and metabolic exposure window. No trial data exists in pregnancy or lactation cohorts. Drug interactions: dose adjustments needed in users on insulin or sulfonylureas due to compounding hypoglycaemia.
Where this stands legally
FDA has not approved IGF-1 LR3. Mecasermin (native IGF-1, brand Increlex) is FDA-approved for paediatric severe primary IGF-1 deficiency; LR3 is sold as a research chemical 'not for human consumption.' Customs scrutiny on imports has tightened.
MHRA has no LR3 approval. Mecasermin is approved as Increlex through EMA/MHRA for the same paediatric indication. WADA prohibits IGF-1 and analogues in competitive sport.
EMA has approved Increlex (mecasermin) for paediatric severe primary IGF-1 deficiency. LR3 has no marketing authorisation. WADA-prohibited.
TGA Schedule 4 for injectable peptides without product registration. Personal-import restrictions apply; ASADA actively tests for IGF-1 analogues in competitive sport.
Not Thai FDA-approved. Available through research-peptide vendors; some Bangkok body-composition clinics compound LR3 in stack protocols. Physician oversight varies sharply.
HSA classifies injectable peptides without product registration as prescription-controlled. LR3 imports for personal use get seized at the border.
Not approved. Available through research-peptide channels and some HCMC body-composition clinics. Vietnam Drug Administration enforcement on research peptides is light.
Available through wellness clinics serving the bodybuilder + expat-athlete market. BPOM has not issued specific LR3 guidance.
Where users say they source it
Names below are sourced from community discussion. None are currently scored against the Panya 11-signal rubric. Panya does not earn commission on any of these. You can search them yourself; treat the list as a starting point for your own diligence, not an endorsement.
- International research-peptide suppliers with COA per lot covering identity by HPLC and mass-spec (the LR3 / native-IGF-1 distinction is a real quality-control failure point; verify the COA matches LR3, not native IGF-1)Pending Panya 11-signal audit
- Body-composition clinics in TH and Bali compounding LR3 in stack protocols (case-by-case physician oversight)Pending Panya 11-signal audit
- Increlex / mecasermin (native IGF-1, prescription-only in approved jurisdictions) for the paediatric IGF-1 deficiency context — distinct molecule, distinct use casePending Panya 11-signal audit
Full vendor scorecards for IGF-1 LR3 land in a follow-up sprint after lawyer review and payment processor selection. We will not route users to any vendor that scores below 70 on the rubric.
Papers worth reading directly
- Francis GL, Aplin SE, Milner SJ et al. (1992) Insulin-like growth factor (IGF)-I and IGF-II in bovine colostrum. Sequences and biological activities of two non-truncated forms of bovine IGF-I and a tryptic fragment. Biochem J →
- Chernausek SD, Backeljauw PF, Frane J et al. (2007) Long-term treatment with recombinant insulin-like growth factor (IGF)-I in children with severe IGF-I deficiency due to growth hormone insensitivity. J Clin Endocrinol Metab →
- Pollak M. (2008) Insulin and insulin-like growth factor signalling in neoplasia. Nat Rev Cancer →
- Tomas FM, Knowles SE, Owens PC et al. (1993) Increased weight gain, nitrogen retention and muscle protein synthesis following treatment of diabetic rats with insulin-like growth factor (IGF)-I and Long-Arg3-IGF-I. Biochem J →
- Backeljauw PF, Underwood LE. (2001) Therapy for 6.5-7.5 years with recombinant insulin-like growth factor I in children with growth hormone insensitivity syndrome. J Clin Endocrinol Metab →
Adjacent reading
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