All peptides / Muscle and bone
IGF-1 LR3
IGF-1 analog
Also IGF1 LR3, LR3 IGF-1, Long R3 IGF-1, Long R3 IGF-I, LR3-IGF-1, IGF-1 Long R3
- Evidence
- CAnimal and cell studies
- FDA status
- Not approvedas of 2026-10-26
- Route
- Injection
- Studies cited
- 0 human1 animal or cell
A lab chemical sold online to build muscle and burn fat. It has never been tested in people.
Sold for
IGF-1 LR3 is sold as a long-acting IGF-1 for muscle growth and fat loss, with claims that it outlasts natural IGF-1 by a day.
Studies say
IGF-1 LR3 is a well characterised laboratory reagent that activates the IGF-1 receptor in cell culture, but it has never been studied in humans, so the grade is C.
Why grade C. For the muscle-growth use IGF-1 LR3 is sold for, no human study exists. The cited material is a review of IGF-1 receptor signalling, a 2019 animal or cell study and a 2026 review of IGF-1 analogs; the compound's documented use is as a growth supplement in laboratory cell culture. 123
FDA. IGF-1 LR3 is not approved by the FDA for any use. It is manufactured as a cell-culture reagent and sold online as a research chemical. 3
Written from 3 cited sources. Last refreshed 2026-10-27. Not physician reviewed.
What this means for you
- What people take it for
- Muscle gain and fat loss
- Can a US doctor prescribe it?
- No. It is not approved and is sold as a research chemical.
- Properly tested in people?
- No meaningful testing published in people; it is a lab reagent.
Evidence checklist
- Randomised controlled trial No human studyno
- Human study over 100 people No human datano
- More than one research group Little beyond a few reviewsno
- Clinical outcomes, not surrogate markers No human outcomesno
- Human safety data beyond case reports No human safety datano
Drawn from the cited studies below. A dash means the sources give no information.
What it is
IGF-1 LR3 (long R3 IGF-1) is an engineered 83-amino-acid version of insulin-like growth factor 1. Two changes were made to the native 70-amino-acid hormone: arginine replaces glutamate at position 3, and a 13-amino-acid extension is added at the N-terminus. Both changes reduce binding to the IGF binding proteins that normally hold IGF-1 in check. 3
It was designed in the 1990s as a reagent for growing cells in serum-free media, where it is cheaper and more effective than native IGF-1 because binding proteins in the culture cannot mop it up. Suppliers sell it by the microgram to laboratories; the same material, repackaged, is what appears on research-chemical sites. 3
How it works
IGF-1 LR3 binds the IGF-1 receptor and switches on the same two pathways as native IGF-1: PI3-kinase/Akt, which drives protein synthesis and cell survival, and Ras/MAP kinase, which drives proliferation. Its receptor affinity is somewhat lower than IGF-1's, but because almost none of it is tied up by binding proteins, far more is free to act, and it persists longer. 13
What human research shows
No human study of IGF-1 LR3 has been published. Animal work has used it in agriculture and physiology experiments because of its stability, but no trial has measured muscle, fat or performance after IGF-1 LR3 in any species for the purpose it is sold. 23
| Study | Model | Finding |
|---|---|---|
| IGF-1 receptor signalling review, 2018 | Narrative review of receptor biochemistry | IGF-1 receptor activation drives PI3-kinase and MAP kinase pathways responsible for growth, differentiation and survival. 1 |
| Scientific Reports 2019 | Laboratory study using IGF-1 LR3 | IGF-1 LR3 was used as a stable IGF-1 receptor agonist in an experimental model. 2 |
Safety
Human safety data do not exist. The hazards would be those of unopposed IGF-1 activity: hypoglycaemia, swelling and joint pain, and the theoretical risk of promoting tumours, since IGF-1 signalling is a growth and survival signal for cancer cells. Laboratory-grade material is not made to be sterile or pyrogen-free for injection. 13
Questions for your clinician
- Has IGF-1 LR3 ever been tested in people for muscle gain?
- Could it lower my blood sugar dangerously?
- Is lab-grade material fit for injection?
Questions people ask
Is IGF-1 LR3 FDA-approved?
No. It is a laboratory reagent with no approved medical use. The approved IGF-1 drug is mecasermin, a different product made for children with severe IGF-1 deficiency. 3
How is IGF-1 LR3 different from IGF-1?
It has an arginine at position 3 and a 13-amino-acid tail at the front, both of which stop IGF binding proteins from capturing it. That makes it more active in cell culture and longer lasting, which is why laboratories use it. 3
Citations
- Hakuno and Takahashi 2018, Journal of Molecular Endocrinology: IGF1 receptor signaling pathways pubmed.ncbi.nlm.nih.gov
- Scientific Reports 2019: experimental study using IGF-1 LR3 doi.org
- Frontiers in Endocrinology 2026: review covering IGF-1 analogs doi.org