Gathering the record
Relay is organizing the evidence and source boundaries.
Engineered low-IGFBP-affinity IGF-1 receptor agonist analogue
An experimental version of a growth-related protein, often discussed for muscle growth and recovery.
Evidence is explained by question. Dosing references show their own check dates.
60-second overview
Why people look into it, what studies found, and what is still unknown.
Educational information only. Evidence reviewed through July 25, 2026. Published studies, sponsor announcements, and trials without results are labeled separately. Evidence gaps apply to the specific finding beside them.
Research questions
Each label shows how much evidence supports that question.
What studies show
No direct human LR3 administration trial was located; the closest human-related work is laboratory analysis using human serum or blood.
It adds a 13-amino-acid N-terminal extension and replaces glutamate with arginine at position 3, reducing binding to IGF-binding proteins.
The traceable LR3 record is laboratory and animal research. Human evidence for native recombinant IGF-1 cannot automatically be assigned to LR3.
Low-binding-protein IGF analogues produced stronger and longer glucose suppression than native IGF-I in pigs and marmosets.
It reduced growth in pigs and increased several organ weights without increasing overall growth in guinea pigs.
An eight-hour cattle study reported a tendency toward protein preservation during food restriction, alongside lower glucose and amino acids.
LR3 increased telomerase activity in prostate-cancer cells and stimulated proliferation in renal-cancer cell lines.
Mecasermin is native recombinant human IGF-1 approved for a narrow pediatric indication. Its hypoglycemia and neoplasia warnings reinforce pathway concerns, but its labeled dosing and pharmacokinetics do not validate LR3 use.
An anti-doping laboratory found abundant oxidized, lower-quality peptide forms in black-market IGF analogue products.
Published LR3 studies used animal and laboratory protocols. Those exposures are not human instructions, and mecasermin labeling is not interchangeable.
The available LR3 record documents molecular behavior, animal metabolism and growth effects, analytical detection, and cell signaling—not validated consumer outcomes.
Risks & unknowns
No direct human LR3 administration trial establishing efficacy, safety, pharmacokinetics, or dosing was located.
No direct evidenceA missed or unpublished study is possible, but no qualifying direct human LR3 treatment trial was found through the evidence cutoff.
Open sourceThe available information does not reliably show how often particular side effects occur.
Evidence boundaryUnder-detected or under-reported events must not be described as rare.
Relay has not verified which side effects led people to stop treatment in studies.
Evidence boundaryThis is an evidence gap, not proof that discontinuations did not occur.
Relay has not verified a compound-specific warning summary for this profile.
Evidence boundaryNot FDA approved; no direct human therapeutic trial was identified Human pharmacokinetics, glucose risk, long-term proliferative and organ effects, feedback suppression, effective exposure, and real-world product identity.
This profile does not contain verified, product-specific emergency instructions.
Evidence boundaryRelay does not infer emergency guidance from study discontinuations, mechanism, or incomplete adverse-event reporting.
Dosing references
Each table labels its source and applies only to the named route, product, or study. An online example or community report is not an approved dose.
IGF-1 LR3 is distinct from approved mecasermin and native IGF-1. Their label doses cannot be transferred to LR3.
What would fill this gap: A verified administered-human regimen for the exact LR3 analogue.
Dosing review checked Oct 20, 2026. Additional sources are available below.No route-specific preparation instructions were verified. A different route or product does not supply them.
Starting dose: the amount used at the beginning of the named label schedule or trial.
Maintenance: the ongoing amount described by that product label.
Trial target: the amount assigned to a study group. Different groups may stop increasing at different targets.
Published administration research located for LR3 used animal models to compare short-term glucose effects with native IGF-1 and related analogues.
Population: Pigs and conscious or anesthetized marmoset monkeys
Design: Bolus comparison of native IGF-I, IGF-I analogues, and insulin
Mechanisms
Long-[Arg3]-IGF-I carries a 13-amino-acid N-terminal extension and an Arg substitution at position 3, reducing affinity for several IGF-binding proteins while preserving IGF1R activity. The published record is preclinical. Animal studies report stronger and more prolonged glucose lowering than native IGF-I, context-dependent protein preservation, suppression of endogenous growth-hormone/IGF pathways, and organ-weight changes without consistent whole-body growth. Human cancer-cell models show proliferative and telomerase signals. Native recombinant IGF-1 (mecasermin) has an FDA-approved pediatric indication and clinically important warnings, but it is a different molecule and cannot supply LR3 dosing, pharmacokinetics, or safety estimates.
A plausible mechanism can explain why a study was attempted. It does not prove that the compound improves a human outcome.
Research reference
A reference for the studies, populations, and routes behind this profile.
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 an instruction for an individual.
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: Animal glucose responses cannot define a human amount, event rate, monitoring plan, or clinical benefit. No verified administered-human route, pharmacokinetic program, or product standard was located. Amounts shown describe cited research exposure—not a dosage recommendation.
Studies
Study arms are reported for transparency. They describe what researchers did in a defined record and do not transfer across identities, routes, formulations, or populations.
A later trial phase can ask a more mature question, but it does not guarantee a positive result, regulatory approval, or relevance outside the studied population.
Mass-spectrometry validation using black-market products, human-serum spiking, human-blood incubation, and rat administration
Laboratory matrices and rats; no human efficacy population
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.
Study administration: Single intramuscular administration in rats for analytical detection
Limitations: This is not a human efficacy or safety trial. Rat detectability does not establish human pharmacokinetics or a reliable commercial-product standard.
Human renal-cell-carcinoma cell-line experiments
Caki-2 and SK-RC-52 renal-cancer cell lines
LR3 and other IGF ligands stimulated proliferation in renal-cancer cell lines, with responses varying by receptor and binding-protein context.
Study administration: IGF-I, LR3 and related IGF ligands with receptor-blockade experiments
Limitations: This is mechanistic laboratory evidence, not a human cancer-incidence study or a quantified clinical risk.
Human prostate-cancer cell-line experiments
LAPC-4, PC-3, and DU-145 prostate-cancer cells
Long-R3 IGF-I increased telomerase activity about three-fold in prostate-cancer cells. The broader IGF-I effect depended on AKT signaling.
Study administration: IGF-I and IGF-I analogues, including Long-R3 IGF-I
Limitations: A cancer-cell experiment is not evidence that LR3 causes cancer in humans. It does show why proliferative and malignancy-related risk questions cannot be dismissed.
High-resolution NMR and restrained molecular-dynamics analysis
Purified Long-[Arg3]-IGF-I; no human participants
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.
Study administration: Structural analysis of isotopically labeled Long-[Arg3]-IGF-I
Limitations: A structure study explains the molecule; it does not establish human effects, half-life, safety, or a treatment protocol.
Eight-hour intravenous infusion study
Food-restricted beef heifers losing body weight
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.
Study administration: Protocol-defined intravenous LR3 infusion versus control
Limitations: The signal was a tendency in food-restricted cattle during an eight-hour experiment—not evidence of muscle gain, recovery, or safety in people.
Four-day controlled infusion experiment
Finisher pigs
LR3 reduced daily weight gain and food intake and suppressed circulating growth hormone, insulin, endogenous IGF-I, and IGFBP-3. Adding growth hormone did not restore the growth response.
Study administration: LR3 with or without porcine growth hormone versus comparator groups
Limitations: A short livestock study cannot predict human outcomes. It directly contradicts the simple assumption that stronger IGF signaling must increase overall growth.
Bolus comparison of native IGF-I, IGF-I analogues, and insulin
Pigs and conscious or anesthetized marmoset monkeys
Low-IGFBP-affinity analogues were about two to three times as potent as native IGF-I at lowering glucose to its nadir and produced roughly four- to eight-fold greater cumulative glucose suppression over four hours. LR3 also lowered plasma amino acids.
Study administration: Species-specific protocol doses of native IGF-I, LR3 and related low-IGFBP-affinity analogues
Limitations: These are animal data. They flag a plausible glucose-lowering hazard but cannot establish a human LR3 dose, event rate, or monitoring plan.
Seven-day continuous-infusion comparison
Female guinea pigs
LR3 increased the fractional weights of the adrenals, gut, kidneys, and spleen but did not increase overall growth, feed efficiency, or carcass composition.
Study administration: LR3, native IGF-I, native IGF-II, or vehicle infusion
Limitations: Organ-weight changes in guinea pigs are a biological signal, not proof of benefit or harm in humans. The study does not define a safe human exposure.
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2025-10-01
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