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evidence · mechanism · dose
Experimental/Anabolic / Growth FactorResearch peptide

IGF-1 LR3

aka Long R3 IGF-1

Long-acting IGF-1 analog that resists IGFBP binding for sustained anabolic signaling.

Educational explainer of a research peptide. Profiles in this section deliberately omit clinical-trial citations, dosing protocols, and purchase links. Not FDA-approved as a supplement; not a recommendation to use.

Overview

IGF-1 LR3 is a recombinant IGF-1 variant with an arginine substitution and an N-terminal extension that reduces binding to IGFBP-3, dramatically extending its half-life and free-fraction activity.

Source
  • Recombinant expression in laboratory cell systems
Forms
  • Subcutaneous injection

Mechanism of action

Binds IGF-1R on muscle, bone, and other tissues, driving PI3K-Akt-mTOR signaling for protein synthesis, hyperplasia, and glucose uptake.

Pathways
  • · IGF-1R then PI3K then Akt then mTOR
  • · GLUT4 translocation
Receptors
  • · IGF-1 receptor
  • · Hybrid insulin/IGF-1 receptors
Hormones
  • · IGF-1 (exogenous)

How it acts on the body

Native IGF-1 is almost entirely sequestered by IGFBP-3, so the bioactive free fraction is small. LR3 carries modifications that prevent this binding, so essentially the full dose remains active and circulates for around 20-30 hours instead of minutes. The result is a steady, strong IGF-1R signal across tissues.

Downstream, IGF-1R activation drives PI3K-Akt-mTOR — the same anabolic axis used by insulin and by mechanical load — producing protein synthesis, satellite-cell activation, and glucose uptake. The latter is also why hypoglycemia is the most acute risk: LR3 has insulin-like effects on peripheral glucose handling.

Hormonal & endocrine impact

How this peptide is reported to shift specific hormones and signaling molecules. Directionality reflects research literature and preclinical models, not clinical prescribing data.

Projected hormonal trajectory
Illustrative curves derived from reported direction of effect. Not measured patient data.

Curves are schematic shapes (sigmoid for increases/decreases, damped oscillation for modulation/stabilization) anchored to a 100% baseline. They communicate direction and tempo of change reported in research literature — not absolute hormone concentrations.

IGF-1 activityIncreases
Free IGF-1R signaling rises substantially for the dosing window.
Growth hormoneDecreases
Exogenous IGF-1 feeds back on the pituitary, suppressing endogenous GH.
Insulin sensitivityModulates
Acute insulin-like glucose lowering, with receptor crosstalk over time.
Thyroid axisModulates
May modestly shift T4 to T3 conversion in some models.

Effects on the body

Increases
Protein synthesis and satellite-cell activation
Increases
Peripheral glucose uptake
Decreases
Endogenous GH

Organ system effects

Skeletal Muscle

Strong anabolic signaling at the muscle fiber.

Liver

Reduced GH-driven IGF-1 output via feedback.

Endocrine

Suppression of natural GH pulses.

Reported effects

Drawn from preclinical research, anecdote, and small-scale clinical observation. No evidence grades are assigned — most peptides on this page lack rigorous human trials.

  • Marked anabolic signaling
  • Potential support for tissue repair

Potential side effects

Common
  • · Hypoglycemia
  • · Injection-site soreness
  • · Lethargy
Rare
  • · Joint pain
  • · Headache
Serious
  • · Cardiac hypertrophy with long-term abuse
  • · Tumor-growth concerns

Drug interactions

Insulin
Compounded hypoglycemia risk.
severe

Pairing context

Often combined with
  • Adequate carbohydrate around dosing
    Blunts hypoglycemia risk.
Avoid combining with
  • Active malignancy
    IGF-1R activation may drive tumor growth.
Important. Research peptides described here are not FDA-approved supplements. Supplement Scholar does not endorse, recommend, or link to any source for purchase. Consult a qualified clinician before considering any peptide therapy.