Education
What Is IGF-1 LR3?
A modified insulin-like growth factor with engineered binding-protein resistance and extended half-life. The entry-level explainer for one of REPRIME's longest-studied peptides.
IGF-1 LR3 is a synthetic variant of native insulin-like growth factor 1 (IGF-1), engineered for substantially longer half-life and weaker binding to the IGF binding proteins (IGFBPs). This is the entry-level explainer; for the structural mechanism behind the modifications, see [IGF-1 LR3: The Long-Acting Variant](/blog/igf-1-lr3-long-acting-variant).
The basics
IGF-1 is a polypeptide hormone produced primarily in the liver in response to growth-hormone signaling. Native IGF-1 has a circulating half-life of around 10 minutes — fast enough that experimental protocols using it have to dose frequently to maintain a stable concentration. IGF-1 LR3 is a modified form that lasts considerably longer in solution.
What 'LR3' means
LR3 stands for 'Long R3':
- **R3** — arginine substitutes glutamic acid at position 3 of the native sequence. This single change weakens binding to IGFBPs, leaving more peptide free to interact with receptors. - **Long** — 13 amino acids appended at the N-terminus. The extension protects against proteolytic clearance.
Together the two modifications extend the effective half-life from minutes to hours.
Why researchers prefer it
For cell-signaling studies, sustained input concentrations matter. A peptide that disappears in minutes makes it difficult to study steady-state response. LR3's longer presence in solution means researchers can observe sustained signaling without continuous re-administration — closer to the integrated biological state being modeled.
Vial sizes
REPRIME offers IGF-1 LR3 in two sizes:
- **100 mcg** — single-protocol or pilot work - **1 mg** — extended protocols
Both vials ship lyophilized at -20°C, with a unique verification code printed on the package insert.
Identity confirmation
LR3 is sometimes confused with native IGF-1 on the market because the names sound similar. REPRIME's COA explicitly confirms the LR3 variant via mass spectrometry — the molecular weight is meaningfully higher than native IGF-1, so the analytical assay distinguishes them cleanly. HPLC further verifies main-peak purity against truncated and oxidized variants that can co-elute on standard reverse-phase columns.
Verification
Every package has a unique verification code. Scan it at [/verify](/verify) on first use.
Shop [IGF-1 LR3](/shop/igf-1-lr3).