- subcutaneous
- intramuscular
IGF-1 LR3
Long R3 Insulin-like Growth Factor-1
IGF-1 LR3 at a glance
Not on either FDA listHow studies gave it
Injected into the fat under the skin, or injected into a muscle
Evidence on this page
3 peer-reviewed papers, published 1995 to 2025
FDA compounding lists
It appears on neither of the two FDA compounding tables.
What it is
A modified analog of human IGF-1 in which glutamic acid at position 3 is replaced with arginine and a 13-amino-acid extension is added to the N-terminus. These modifications dramatically reduce binding affinity for all six IGF binding proteins (IGFBPs), resulting in a much higher free bioactive fraction compared to native IGF-1.
IGF-1 LR3 is approximately 3× more potent than native IGF-1 in cell proliferation assays and activates the PI3K/Akt/mTOR and MAPK/ERK pathways. It has been studied in animal models for effects on organ growth, intestinal epithelial proliferation, and protein anabolism. No human clinical trials have been conducted with this specific compound.
The FDA-approved recombinant IGF-1 product (mecasermin/Increlex) uses the native 70-amino-acid sequence, not the LR3 variant.
Published research
Animal studies have examined IGF-1 LR3 across models including intestinal epithelial proliferation in rats (Steeb et al., 1995), organ growth in guinea pigs and fetal sheep, and amyloid plaque remodeling in Alzheimer's mouse models (2024). The compound's reduced IGFBP binding and extended bioactivity relative to native IGF-1 are well-characterized in vitro.
No peer-reviewed human clinical trials have been conducted with IGF-1 LR3 as of March 2026. All human clinical data for the IGF-1 class uses native-sequence recombinant IGF-1 (mecasermin). Community dosing ranges are extrapolated from animal data and are not clinically validated.
What the terms on this page mean5 termsHide
- analog
- A molecule built to copy a natural one with a deliberate change, usually to make it last longer or bind more tightly.
- IGF-1
- Insulin-like growth factor 1, made largely in the liver in response to GH, and the marker most GH studies measure.
- animal model
- A test in animals standing in for the human condition. Results often fail to carry over to people.
- clinical trial
- A study that tests something in people under a written plan, with results recorded.
- in vitro
- In a dish. Cells or tissue tested outside a living body.
Compounding status
Not on either FDA list- FDA listing
- IGF-1 LR3 appears on neither FDA's category 2 table nor its table of withdrawn nominations.
- What that means
- Absence from both lists is not permission to compound. Section 503A allows a bulk drug substance only where a USP or NF monograph exists, or the substance is a component of an FDA-approved drug product, or it appears on the 503A bulks list.
Source: Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks, FDA. Content current as of 2026-04-22; read 2026-09-05. This describes what a compounding pharmacy may supply. It is not advice about your own use.
Also given subcutaneous
- IpamorelinIpamorelin AcetateFDA category 2
- KisspeptinKisspeptin-10 / Kisspeptin-54 (Metastin)FDA category 2
- KPVLysine-Proline-Valine (α-MSH C-terminal tripeptide)Nomination withdrawn
- LiraglutideLiraglutide (acylated GLP-1(7-37) analog)Not on either FDA list
- LL-37LL-37 (Cathelicidin Antimicrobial Peptide / hCAP18 C-terminal fragment)Nomination withdrawn
- Melanotan IIMelanotan II (Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2)Nomination withdrawn
Where this came from3 referencesHide
Each one was resolved at PubMed and confirmed to be the work this page cites. Author, title, journal and year come from the PubMed record, not from the page text.
- Administration of insulin-like growth factor-I (IGF-I) peptides for three days stimulates proliferation of the small intestinal epithelium in rats
Steeb CB, Trahair JF, Read LC. Gut (1995). PMID 8549937.
- Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris
Lu Z, et al.. Applied microbiology and biotechnology (2023). PMID 37261455.
- Intranasal long R3 insulin-like growth factor-1 treatment promotes amyloid plaque remodeling in cerebral cortex but fails to preserve cognitive function in male 5XFAD mice
Engel MG, et al.. Journal of Alzheimer's disease : JAD (2025). PMID 39610283.
About this page
Reviewed 2026-08-11. This page reports what published studies and FDA documents say. It carries no dose, cycle length or stack, and it does not tell you whether a substance is appropriate for you. Side-effect reports circulating on forums are self-reported rather than measured, so they are not republished here.
See the editorial policy for how corrections are handled.