Engineered low-IGFBP-affinity IGF-1 receptor agonist analogue
IGF-1 LR3 is a modified IGF-1 research protein designed to avoid IGF-binding proteins and remain more biologically available in laboratory systems. People commonly research it for muscle growth, recovery, and body composition, but no direct human LR3 treatment trial was found. Animal studies also show prolonged glucose lowering, hormone feedback changes, and inconsistent growth effects.
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Depth and confidence summarize the research record—not effectiveness, safety, or a recommendation.
Molecular, animal, analytical, and cell studies exist, but no direct human administration trial was located.
Research depth describes how large and mature the overall record is. It does not tell you whether the results were positive.
The molecule is biologically active in preclinical systems, while human efficacy, safety, pharmacokinetics, and amount remain unknown.
Confidence describes how reliable and consistent the conclusions are. It can be high for one outcome and low for another.
The strongest evidence type shows what the best-supported conclusions are actually based on.
Human findings are more directly relevant than animal or laboratory results, but they still apply only to the populations and outcomes studied.
Route-specific record
These are exposures used in cited research for a specific route and population—not a suggested amount.
Half-life describes how long it takes the measured amount in the body to fall by half. It is not a dosing recommendation.
Evidence can change by administration method. Findings from one route should not automatically be applied to another.
Evidence boundary: Commercial use and online half-life claims cannot replace a direct human study. Native IGF-1/mecasermin labeling does not apply to LR3. Amounts shown describe cited research exposure—not a dosage recommendation.
Practical starting point
Common goals and questions—not recommendations or promises of benefit.
The overview, studies, and source ledger below explain what supports each label—and where the evidence stops.
What the evidence says
No direct human LR3 administration trial was located; the closest human-related work is laboratory analysis using human serum or blood.
This is the strongest supported conclusion in the current human evidence—not a summary of every claim made about the compound.
Human pharmacokinetics, glucose risk, long-term proliferative and organ effects, feedback suppression, effective exposure, and real-world product identity.
Keeping the main uncertainty visible prevents an early or promising finding from looking more settled than it is.
The evidence story
Importance shows how much an item changes the evidence story. Quality shows how much confidence the design deserves. A strong negative study can score highly on both.
Importance and quality answer different questions. A rigorous study can be highly important even when it challenges a popular claim.
The method detected LR3-related products after rat administration. Black-market samples contained abundant oxidized, lower-quality peptide forms. The authors stated that these analogues had never been approved for human use.
LR3 and other IGF ligands stimulated proliferation in renal-cancer cell lines, with responses varying by receptor and binding-protein context.
Long-R3 IGF-I increased telomerase activity about three-fold in prostate-cancer cells. The broader IGF-I effect depended on AKT signaling.
LR3 contains a Glu-to-Arg substitution at position 3 and a 13-amino-acid N-terminal extension. Its IGF-I domain remains broadly similar to native IGF-I, while the modified N terminus helps explain lower binding to IGF-binding proteins.
LR3 tended to preserve whole-body and skeletal-muscle protein in catabolic heifers, while markedly lowering plasma amino acids and glucose and changing endogenous IGF concentrations.
Administration and handling
Published LR3 papers describe intravenous infusions, bolus injections, implanted-pump delivery, or intramuscular analytical exposures in animals. No direct human LR3 dose-finding, route-comparison, pharmacokinetic, or safety trial was located. Animal doses must not be converted into human doses, and the approved mecasermin label cannot be substituted because mecasermin is native recombinant IGF-1 rather than LR3. The evidence does not support a starter dose, cycle, injection frequency, stacking plan, or self-monitoring protocol.
No FDA-approved LR3 product label or regulator-validated consumer reconstitution, storage, sterility, or beyond-use standard was identified. A 2021 anti-doping study found abundant oxidized, lower-quality peptide forms in sampled black-market IGF analogues. Seller instructions and a peptide name cannot establish identity, concentration, purity, sterility, aggregation state, stability, or biological activity. Mecasermin handling instructions apply to its approved formulation, not LR3 powders.
Primary-source ledger
2025-10-01
2021-07-01 · PMID 33587816 · DOI 10.1002/dta.3016
2004-11-01 · PMID 15492822
2003-07-01 · PMID 12843187 · DOI 10.1210/jc.2002-021326
2000-04-07 · PMID 10744677 · DOI 10.1074/jbc.275.14.10009
1999-05-01 · PMID 10370861 · DOI 10.1016/S0739-7240(99)00015-6
1997-12-01 · PMID 9488001 · DOI 10.1677/joe.0.1550559
1997-11-01 · PMID 9415072 · DOI 10.1677/joe.0.1550377
1995-08-01 · PMID 7561636 · DOI 10.1677/joe.0.1460247