IGF-1 LR3
Long R3 IGF-I
IGF-1 LR3 is a modified insulin-like growth factor built as a laboratory cell-culture reagent, not as a medicine.
Regulatory status: Not a medicine anywhere. It has never been tested in a human trial. Recombinant human IGF-1 (mecasermin) is a separate, approved drug — a different molecule.
Default vial
1 mg
Default mix
2 mL
Reported range
No published human dose
Draw (U-100)
10 u
A modified IGF-1 built as a cell-culture reagent: the changes make it resist the binding proteins that normally control IGF-1 in the body. It has never been trialled in people. Recombinant human IGF-1 (mecasermin) is a different, approved medicine.
Where these numbers come from
No published study reports a dose for this compound in people. The figures here exist only so the calculator can run — they are not a recommendation. Long R3 IGF-I is a laboratory reagent; the published work is cell culture and livestock research, and it has never been trialled in people.
- Detection of His-tagged Long-R3-IGF-I in a black market product, Growth Horm IGF Res 2010
- IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep, Am J Physiol Endocrinol Metab 2025
Reviewed October 2026
What it is
- IGF-1 with two changes: an arginine substitution at position 3, and a 13-amino-acid extension on the N-terminus.
- Those changes stop it binding the IGF binding proteins that normally control how much free IGF-1 the body has — which is precisely why it is useful in a culture dish and concerning in a person.
- Sold as a reagent for cell and livestock research.
- Not mecasermin: that is unmodified recombinant human IGF-1, an approved medicine for severe primary IGF-1 deficiency.
How it is described to act
- 1
No human pharmacokinetic study has been published.
- 2
Because it evades the binding proteins, far more of it stays free and active than would be the case for natural IGF-1.
- 3
Acts at the IGF-1 receptor, which drives growth and anabolic signalling in most tissues.
- 4
In culture this produces strong, sustained stimulation; what it does over time in a person has not been studied.
What the research has looked at
What it is actually used for
- The published work is cell culture, livestock and fetal animal physiology — for example studies in neonatal calves (Am J Physiol, 1997) and fetal sheep.
- A 2025 study reported that IGF-1 LR3 did not promote growth in late-gestation growth-restricted fetal sheep, which is a negative result in one of the models it has actually been tested in.
- It also appears in recombinant protein production and tissue engineering papers — laboratory uses, not therapeutic findings.
Already circulating outside the lab
- A 2010 paper in Growth Hormone & IGF Research reported detecting His-tagged Long-R3-IGF-I in a black market product — that is, material carrying a purification tag from protein expression, sold for injection.
- A His tag is something you leave on a protein for laboratory convenience, not something intended to go into a person.
Strength of evidence: Preclinical evidence only
No human trial exists. The compound was designed as a research reagent, and the published literature is animal and cell work.
What is published comes from cell and animal studies. Findings in those models frequently do not carry over to people.
Reported cautions and unknowns
- There is no human safety data of any kind.
- Escaping binding-protein regulation is the whole design intent, and it removes the mechanism the body uses to limit IGF-1 activity.
- IGF-1 receptor signalling promotes cell growth and survival generally, including of cells one would not want to promote. Sustained unregulated stimulation has not been assessed in people.
- IGF-1 can lower blood glucose through cross-reactivity at the insulin receptor.
- Published analysis has found black-market material carrying laboratory purification tags.
References
- 1.Detection of His-tagged Long-R3-IGF-I in a black market product, Growth Horm IGF Res (2010)
- 2.IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep, Am J Physiol Endocrinol Metab (2025)
- 3.The somatotropic axis in neonatal calves can be modulated by nutrition, growth hormone, and Long-R3-IGF-I, Am J Physiol (1997)
Handling this vial
- Lyophilized vials are generally stored at 2–8 °C and kept out of light; once reconstituted with bacteriostatic water they are refrigerated and commonly discarded after 28 days.
- Mix by aiming water down the vial wall and rolling gently — do not shake — and never re-freeze a reconstituted vial.
- Pep-Tidy cannot verify what is in your vial. Ask your supplier for a current Certificate of Analysis (HPLC/MS).
IGF-1 LR3 questions people ask
How do you reconstitute IGF-1 LR3?
A common starting point for a 1 mg vial of IGF-1 LR3 is 2 mL of bacteriostatic water, which gives 0.5 mg per mL. Aim the water down the inside wall of the vial, let it dissolve on its own, and roll gently instead of shaking. Pep-Tidy's reconstitution calculator will recalculate the numbers for any other vial size or water volume you use.
How many units of IGF-1 LR3 is one dose?
At 0.5 mg per mL, that works out to about 10 units on a U-100 insulin syringe for a 50 mcg dose. Change the vial size, water volume, or target dose in the calculator and the syringe reading updates with it. This is arithmetic, not a dosing recommendation.
What dosing schedule is reported for IGF-1 LR3?
Published and community sources describe No published human dose, subcutaneous, every day, typically run 4 weeks on and 4 weeks off. These figures describe what has been reported, not what anyone should take — talk to a licensed clinician first.
How should IGF-1 LR3 be stored?
Lyophilized IGF-1 LR3 vials are generally kept at 2–8 °C and out of light. Once reconstituted with bacteriostatic water they are refrigerated and commonly discarded after about 28 days. Never re-freeze a reconstituted vial and never shake it.
Read this before you act on anything above
Everything on this page is a summary of what other people have published — it is not medical advice, not a recommendation, and not a dosing instruction. Reported dose ranges describe what appears in the literature or in community protocols, not what anyone should take. Talk to a licensed clinician before using any peptide.