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IGF-1 LR3

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IGF-1 LR3

TL;DR

IGF-1 LR3 is a synthetic 83-amino-acid analog of human IGF-1 with reduced IGFBP binding affinity. It is research-only, has no human clinical trials, no FDA/EMA approval, and is WADA-prohibited. The primary acute safety risk is hypoglycemia (IGF-1 cross-activates the insulin receptor). The primary chronic risk is elevated cancer risk (confirmed in UK Biobank n≈400,000). No human PK data exists specifically for LR3. Human IGF-1 trials consistently show lean mass increases without strength or functional improvement.

What It Is

IGF-1 LR3 (Long R3 IGF-1) differs from native 70-AA human IGF-1 by:

  1. A single amino acid substitution: glutamate → arginine at position 3 (“R3”)
  2. A 13-amino-acid N-terminal extension (83 AA total)

Purpose of the modification: The Glu→Arg substitution disrupts the IGFBP-binding interface, reducing IGFBP-3 affinity ~100-fold (PMID:1713161). Less IGFBP sequestration → higher fraction of free peptide available to activate IGF1R.

Not the same as MGF. Mechano Growth Factor (MGF/IGF-1Ec) is an alternatively spliced IGF-1 transcript variant sharing the identical 70-AA mature sequence with native IGF-1 but carrying a distinct C-terminal E-domain. The truncated “Goldspink-MGF” peptide (24–25 AA E-domain fragment) sold on grey markets shows no measurable IGF1R activation in vitro (PMCID:PMC4798685).

Not approved anywhere. IGF-1 LR3 is a research reagent only. Native IGF-1 (mecasermin/Increlex) is FDA/EMA-approved, but only for severe primary IGF-1 deficiency (SPIGFD) in children — not for anabolic or performance use.

Why It Matters for Vitals

DimensionRelevance
GlucoseIGF-1 cross-activates the insulin receptor; hypoglycemia is the primary acute safety risk — CGM monitoring is non-negotiable for any off-label use
Body compositionHuman IGF-1 trials consistently show lean mass increases without strength or functional improvement; no LR3-specific human data exists
RecoveryIGF1R activation drives PI3K-Akt-mTORC1 protein synthesis + FoxO inhibition (reduced ubiquitin-proteasome degradation); mechanistic support for recovery, not demonstrated in humans for LR3
HRV / readinessNo direct human data; chronic IGF-1 excess produces acromegaly-like features including cardiovascular changes
Cancer riskUK Biobank (n≈400,000): higher IGF-1 is associated with increased breast, prostate, colorectal, thyroid, kidney cancer; Laron syndrome cohort shows near-zero cancer in congenital IGF-1 deficiency
DetectionNo validated wearable detection model for IGF-1 LR3 use
CoachingNo basis for recommending this compound; the risk-benefit profile does not support any Vitals-relevant use case

Mechanism Summary

Receptor binding

  • Binds IGF1R with approximately comparable intrinsic affinity to native IGF-1 (assay-dependent variation)
  • Reduced IGFBP binding → higher free fraction → more IGF1R engagement per unit concentration
  • IGF1R activation downstream cascade (identical to native IGF-1):
    • PI3K-Akt-mTORC1 axis: protein synthesis
    • Ras-Raf-MEK-ERK1/2 axis: mitogenic/anabolic effects in muscle cells
    • FoxO inhibition: reduces MAFbx/Atrogin-1 and MuRF1 (ubiquitin-proteasome protein degradation)
    • Myostatin cross-inhibition: partial block via Akt downregulation of ActRIIB and Smad3 sequestration

Tachyphylaxis risk

Prolonged IGF ligand exposure induces IGF1R downregulation via β-arrestin recruitment, clathrin-mediated endocytosis, and lysosomal degradation (PMID:1713161; PMCID:PMC4055838). IGF-1 LR3, by evading IGFBP buffering, may be more prone to driving its own receptor downregulation vs. native IGF-1. Time course and extent in humans is unknown.

CNS penetration

Systemic LR3 does not efficiently cross the blood-brain barrier. Intranasal administration (olfactory/trigeminal pathways) has been studied in mouse models only (PMID:39641473/PMCID:PMC12617435).

Human Evidence Summary

All human data below is for native-sequence rhIGF-1 (mecasermin/Increlex) unless otherwise noted. Zero LR3-specific human efficacy trials exist.

IndicationCompoundResultCitation
ALSrhIGF-1Phase III, N=330: NULL — no benefit on any endpointPMID:19029516
DMDrhIGF-1Lean mass ↑; 6-min walk distance nullPMID:32108355
Myotonic Dystrophy Type 1rhIGF-1/IGFBP-3Lean mass ↑; grip strength and function nullPMID:20837825
Healthy Postmenopausal WomenrhIGF-11-year RCT: NULL — no body composition, strength, bone density, or cognitive benefitPMID:14960008
GHD AdultsGH meta-analysisLean mass ↑; strength nullPMID:19769614
Laron Syndrome / SPIGFDrhIGF-1Growth velocity significantly improvedPMID:8521188
5XFAD Alzheimer’s mouseLR3 (intranasal)Plaques ↓; cognition nullPMID:39641473

Consistent pattern: In every human IGF-1 trial in populations without confirmed IGF-1 deficiency, lean mass or protein synthesis increases fail to translate into strength or functional improvements.

Safety and Risks

Hypoglycemia — Primary Acute Risk

  • 25–42% of mecasermin patients experience hypoglycemia
  • IGF-1 cross-activates the insulin receptor; suppresses hepatic glucose output; increases peripheral glucose utilization
  • Severe hypoglycemia and seizures are documented
  • Life-threatening in combination with insulin, sulfonylureas, or other glucose-lowering agents
  • CGM monitoring is non-negotiable for any off-label use context

Cancer Risk — Confirmed Epidemiological

  • UK Biobank (n≈400,000): higher circulating IGF-1 associated with breast, prostate, colorectal, thyroid, kidney cancer (PMCID:PMC10505533)
  • IGF-1 induces hypoglycemia and skin/mammary tumors in rodent carcinogenicity studies
  • Laron syndrome cohort: near-zero cancer and diabetes mortality
  • Active malignancy is an absolute contraindication

Organ Hypertrophy

  • Fetal sheep IUGR: LR3 did not increase organ masses (PMID:39679943)
  • Normal fetal sheep: 35% heart weight increase with LR3 (distinct from IUGR study — must not be conflated)
  • Adult guinea pig: selective increases in adrenal, gut, kidney, and spleen weights without BW gain (PMID:7561636)
  • Chronic human IGF-1 excess produces acromegaly-like features: coarsened facies, organomegaly, insulin resistance, cardiovascular disease

Other Risks

  • Tonsillar/adenoidal hypertrophy: ~15% of pediatric mecasermin patients
  • Intracranial hypertension: documented class effect
  • Injection site lipohypertrophy: ~12%
  • Grey-market product quality: purity ranges ~1–100%; endotoxin contamination documented; CoAs unreliable

WADA Status

Explicitly prohibited under WADA 2026 Prohibited List, S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), at all times (in- and out-of-competition).

Pharmacokinetics

  • No human LR3-specific PK data exists
  • Native IGF-1 SC half-life in humans: ~20 hours
  • Animal data (rat, pig): LR3 analogs with reduced IGFBP binding show faster plasma clearance and larger volume of distribution vs. native IGF-1
  • The widely cited “20–30 hour half-life” claim for LR3 is unsupported; it conflates native IGF-1 half-life with LR3 and has no traceable primary citation
  • Intranasal LR3 studied only in mouse models

Dosing Myth

The common grey-market dosing range of 20–100 mcg/day has no clinical basis. No dose-response data exists for LR3 in any human population.

What Stays Inside This Hub

  • IGFBP evasion structural details (single-compound specific)
  • Satellite cell biology (too specific for a separate mechanism note)
  • IGF1R tachyphylaxis kinetics (inside hub — no reuse case)
  • MGF vs. LR3 distinction (hub only)
  • Formulation and reconstitution logistics
  • Grey-market quality issues
  • Animal PK specifics

Linked MOCs and Maps

Safety

Mechanism / Shared Biology

Biometrics (aspirational — no separate note)

  • HRV — aspirational link; no specific IGF-1 HRV data
  • Glycemic Variability — aspirational link; hypoglycemia risk connects

Comparisons

Source: igf-1-lr3-canonical.md · BATCH118 · Evidence synthesis: 10-worker lane protocol · Status: Research-Only Compound

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