IGF-1 LR3Growth Hormone

Long-acting IGF-1 analog studied for growth and recovery.

Peptides·Index rating

1/5Speculative

Human data

Safety

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Quick factsat a glance

Status: Research / not approved
Developer: Recombinant Long [Arg3] IGF-1 analog (research/cell-culture origin; not FDA-approved)
Receptors / target: IGF-1 receptor agonist; a Glu3->Arg3 substitution plus a 13-amino-acid N-terminal extension sharply lowers IGF-binding-protein binding, raising free bioactivity and potency
FDA-approved?: NO
Prescription available?: NO
Studied for: IGF-1 receptor signalingmuscle hypertrophy / anabolic researchcell-culture & bioprocessinggrowth & metabolism

Overview

IGF-1 LR3 (Long [Arg3]-IGF-1) is a recombinant analog of insulin-like growth factor 1, engineered with a glutamate-to-arginine substitution at position 3 and a 13-amino-acid N-terminal extension that sharply reduce its binding to IGF-binding proteins (Francis et al., 1992). It is sold and used primarily as a cell-culture reagent and taken off-label in bodybuilding. Critically, IGF-1 LR3 is not mecasermin (recombinant human IGF-1, brand Increlex), the FDA-approved drug for severe primary IGF-1 deficiency — none of mecasermin's approval or trials apply to LR3. There are no human therapeutic trials of IGF-1 LR3 itself; the evidence base is animal and in-vitro.

Mechanism

LR3-IGF-1 acts as an agonist at the IGF-1 receptor, triggering PI3K/Akt and Ras/MAPK signaling that promotes cell growth, survival and protein synthesis. Because roughly 98% of native circulating IGF-1 is sequestered by IGF-binding proteins, the analog's two modifications greatly lower IGFBP affinity, leaving more peptide free to engage the receptor — yielding higher potency and a longer half-life. Paradoxically, animal infusion studies show systemic feedback in which LR3-IGF-1 suppresses growth hormone, endogenous IGF-1 and IGFBP levels (Conlon 1995; Dunaiski 1997).

Clinical evidence

There are no human therapeutic clinical trials of IGF-1 LR3. The available evidence is preclinical: the original biochemical characterization in cell systems (Francis et al., 1992) and infusion studies in guinea pigs (Conlon et al., 1995) and pigs (Dunaiski et al., 1997), where effects on organ growth and circulating hormones were variable and sometimes growth-suppressing. Human use is off-label/non-medical, and efficacy or safety in people has not been established; mecasermin trials are a separate drug and must not be cited as evidence for LR3.

Safety profile

IGF-1 LR3 has no human safety data, so its risk profile is inferred from IGF-1 pharmacology. As a potent IGF-1R agonist it can cause hypoglycemia, and chronic IGF-1 signaling carries a theoretical risk of promoting proliferation of existing or latent neoplasia. Animal studies show unpredictable systemic endocrine effects, including suppression of growth hormone and the endogenous IGF axis. It is not FDA-evaluated and is prohibited in sport at all times as a growth factor on the WADA Prohibited List. Research use only; nothing here is medical or dosing guidance.

Timelinecommonly reported

Per dose (acute)
Insulin-like activity can lower blood glucose acutely; the LR3 modification extends activity versus native IGF-1.
Weeks 1–6
No human trials of IGF-1 LR3 exist. Anecdotal bodybuilding use claims muscle effects over weeks, but this is unstudied, and the long-term proliferative/oncologic risk is unknown.

Reported side effectsreported in literature

Reported in published literature and user reports. Not a complete list, and not medical advice.

Hypoglycemia (insulin-like activity)
Localized tissue/organ growth
Headache, dizziness
Theoretical proliferative / tumor-growth risk

If severe or unexpected symptoms occur, contact a qualified medical professional. PEPTIDES·INDEX does not provide medical advice.

Cautionsdiscuss with a clinician

Use caution or avoid if

No human safety or contraindication data exist for IGF-1 LR3; the items below are grounded theoretical cautions inferred from IGF-1 pharmacology, not established contraindications.
Active or latent neoplasia is a theoretical concern because chronic IGF-1R signaling can promote cell proliferation.
Conditions involving hypoglycemia risk, since IGF-1 LR3 has insulin-like activity that can lower blood glucose.

Interactions

Insulin or other glucose-lowering agentsAdditive hypoglycemia risk is plausible given IGF-1 LR3's insulin-like activity; not characterized in humans (research use only)
Other agentsNo documented human drug interactions; the compound is uncharacterized in humans (research use only)

Compare

vs MOTS-c
Another research-only metabolic peptide with no interventional human trials; both lack human safety data.

FAQ

Is there any human trial of IGF-1 LR3?

No. There are no human therapeutic clinical trials of IGF-1 LR3 itself; the evidence base is animal and in-vitro. It is sold primarily as a cell-culture reagent and used off-label in bodybuilding.

Is IGF-1 LR3 the same as mecasermin (Increlex)?

No. Mecasermin is recombinant human IGF-1, an FDA-approved drug for severe primary IGF-1 deficiency. IGF-1 LR3 is a different, modified analog with no FDA evaluation, and none of mecasermin's approval or trial data apply to it.

Is IGF-1 LR3 banned in sport?

Yes. As a growth factor it is prohibited at all times on the WADA Prohibited List.

What do the two modifications in Long R3 IGF-1 do?

IGF-1 LR3 has a glutamate-to-arginine substitution at position 3 plus a 13-amino-acid N-terminal extension. Together these sharply lower its affinity for IGF-binding proteins, so more of the peptide stays free to engage the IGF-1 receptor, which raises its potency and lengthens its half-life relative to native IGF-1.

Why is hypoglycemia a concern with IGF-1 LR3?

IGF-1 LR3 is a potent IGF-1 receptor agonist and IGF-1 has insulin-like activity, so it can lower blood glucose. That effect is plausibly additive with insulin or other glucose-lowering agents, but it has not been characterized in humans and the compound is research-use-only.

Does IGF-1 LR3 behave the same way in the body as native IGF-1?

Not entirely. Beyond its higher free bioactivity, animal infusion studies show paradoxical systemic feedback in which Long R3 IGF-1 suppressed growth hormone, endogenous IGF-1 and IGF-binding-protein levels (Conlon 1995; Dunaiski 1997), so its whole-body effects can differ from simply adding more IGF-1.

Similar compounds

MOTS-cLongevityMitochondrial peptide studied for metabolism and endurance.IpamorelinGrowth HormoneSelective GH secretagogue, often paired with CJC-1295.CJC-1295 (No-DAC)Growth HormoneShort-acting GHRH analog (Mod GRF 1-29) studied for growth-hormone release; often paired with Ipamorelin.

Sources

Starting references for the library summary. These are not dosing instructions or medical advice.

Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potencyJournal of Molecular Endocrinologypubmed.ncbi.nlm.nih.gov/1378742/…Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pigJournal of Endocrinologypubmed.ncbi.nlm.nih.gov/7561636/…Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigsJournal of Endocrinologypubmed.ncbi.nlm.nih.gov/9488001/…Insulin-Like Growth Factor-1 (IGF-1) and Its Monitoring in Medical Diagnostic and in SportsBiomoleculespubmed.ncbi.nlm.nih.gov/33557137/…IGF-1 and the World Anti-Doping Agency Prohibited ListU.S. Anti-Doping Agencywww.usada.org/spirit-of-sport/igf-1-and-the-world-an…

For research-use educational context only. Not medical advice and not a recommendation to use any compound. Consult a qualified healthcare professional before any health decision.