IGF-1 LR3

IGF-1 LR3 (Long Arginine 3-IGF-1) is a synthetic peptide and a modified analogue of human insulin-like growth factor-1 (IGF-1). It is engineered to be more stable and potent than natural IGF-1, consisting of 83 amino acids compared to the 70 amino acids in native IGF-1. IGF-1 LR3 is often typed as IGF1LR3 which is an easier version of the same.

Key Benefits

• IGF-1 LR3 May support lean muscle growth and muscle cell recovery
• Commonly researched for improving tissue repair and exercise recovery
• May help enhance nutrient utilization and cellular growth processes
• Research suggests potential benefits for performance support, recovery, and muscle preservation

FDA-Approved Uses

IGF1LR3 has NO FDA-approved use. It is a synthetic modified research analogue of human IGF-1, designed primarily as a laboratory tool for studying IGF-1 receptor signaling.

Regulatory Status

• Not on the FDA 503A Bulks List — cannot be legally compounded by licensed 503A pharmacies
• Not a controlled substance — possession for research use is technically legal
• Sale or marketing for human consumption is illegal under FDA regulations (FDA-stated position)
• No NDA or IND application filed for IGF-1 LR3
• No clinical trial program underway for IGF-1 LR3 specifically

Related FDA-approved product (NOT IGF-1 LR3)

Mecasermin (INCRELEX) — native recombinant human IGF-1 (rhIGF-1)
FDA-approved for severe primary IGF-1 deficiency in children (growth failure)
AND for growth hormone gene deletion with neutralizing antibodies to GH
[IGF-1 LR3 is a MODIFIED ANALOGUE — distinct from mecasermin; they are NOT interchangeable]

WADA 2026: Prohibited at all times under S2 — ‘IGF-1 and its analogues’ (explicitly includes LR3 variant)

Conditions under research investigation (animal/in vitro — no human RCTs for IGF1LR3):

• Muscle hypertrophy and anabolic effects (bodybuilding/performance enhancement research)
• Tissue repair and wound healing
• Neuroprotection
• Muscle wasting / sarcopenia (mechanistic research)
• Metabolic regulation

Trade Names in the USA and Manufacturers

No FDA-approved trade name or manufacturer in the USA.

Molecular identity

83-amino acid modified analogue of human IGF-1 (native IGF-1 has 70 amino acids)
Two key modifications vs. native IGF-1:
1. Substitution: Glutamic acid (Glu) → Arginine (Arg) at position 3 (‘R3’ designation)
2. Extension: Additional 13 amino acids added at N-terminus (MFPAMPLLSLFVN — ‘Long’ designation)

These modifications dramatically reduce binding to IGF-binding proteins (IGFBPs)

• Result: Higher free (active) fraction in circulation; extended half-life (~20–30 hours vs. ~15 minutes for native IGF-1)
• MW: ~9,117 Daltons
• Molecular formula: C₄₀₀H₆₂₅N₁₁₁O₁₁₅S₉ (approximate)

US availability:
– Research chemical vendors (‘research use only’): Widely available as lyophilized powder
– NOT available through licensed US compounding pharmacies (not on 503A Bulks List)
– Some international online pharmacies ship to US (legal grey area)

Original development: Genentech research tool; licensed to research suppliers

Dosage

Subcutaneous injection (most common):
Typical dose range: 20–100 mcg per injection
Most reported doses: 40–80 mcg per injection
Frequency: Once daily
Timing: Post-workout (most common in bodybuilding protocols; muscle IGF-1 uptake may be enhanced)
Alternative: Multiple site injections (site-specific theory — see note below)
Cycle length: 4–6 weeks maximum (then equal time off — receptor desensitization risk)

Intramuscular injection (some protocols):
Injected directly into trained muscle group
Dose: 20–50 mcg IM per site

Note on ‘site-specific growth’ claim:
Some protocols advocate for injecting into the specific muscle for localized growth effects.
Evidence basis: Animal and in vitro data only.
Reality: IGF-1 LR3 distributes systemically after SC or IM injection — localized effect is not confirmed in humans.

Critical timing note:
ALWAYS inject post-meal or with food — NEVER in a fasted state.
IGF-1 LR3 has weak insulin receptor activity + high free fraction = significant hypoglycemia risk when fasted.

Reconstitution: Lyophilized powder; reconstitute with Bacteriostatic Water (1 mL); store at -20°C lyophilized; stable 4 weeks refrigerated after reconstitution.

Pricing

No FDA-approved commercial pricing.

Research peptide vendors (unregulated):
100 mcg vial: ~$15–$35
1 mg vial: ~$40–$80
Monthly cost (50 mcg/day, 30 days): ~$100–$250/month depending on vendor and vial size

Note: IGF-1 LR3 is typically more expensive per microgram than most GHRH/GHRP peptides due to its more complex synthesis (83 amino acids).

Tips

• IGF-1 LR3 has the HIGHEST HYPOGLYCEMIA RISK of any peptide in this document class; higher than native IGF-1 (mecasermin) due to reduced IGFBP binding and a larger free fraction. NEVER inject fasted.
• WADA S2 prohibited (‘IGF-1 and its analogues’): Do NOT use if subject to anti-doping testing. Prohibited at all times, in and out of competition.
• Zero published human RCTs for IGF-1 LR3 for body composition exist. All efficacy claims rest on rodent data and native IGF-1 (mecasermin) trials a different molecule.
• Cycle length MUST be limited to 4–6 weeks maximum. Extended IGF-1 LR3 use causes IGF-1 receptor desensitization; reducing effectiveness and may cause unwanted organ/tissue growth (particularly intestinal hypertrophy).
• Cancer risk is the most serious long-term concern. IGF-1 promotes cellular proliferation via the same pathways implicated in tumor growth. IGF-1 LR3 stays active 40–120x longer than native IGF-1 in circulation.
• Do NOT combine with insulin — the combined risk of severe hypoglycemia is significant and potentially fatal. This combination is documented in performance-enhancing drug fatalities.
• IGF-1 LR3 is NOT mecasermin (INCRELEX) — do not confuse the FDA-approved pediatric drug with this unapproved research analogue.

Side Effects

Most significant risk:
– HYPOGLYCEMIA (most serious and acute risk):
IGF-1 LR3 has weak but real insulin receptor (IR) binding activity + very high free fraction (low IGFBP binding) = significant glucose-lowering effect, especially in fasted state.
Mecasermin (native IGF-1) already causes hypoglycemia in ~50% of pediatric patients. IGF-1 LR3 is theoretically higher risk due to 40–120x longer active exposure time.
Fetal sheep model: High-dose IGF-1 LR3 infusion induced severe hypoglycemia and hypoxemia.

Commonly reported in off-label use:
– Hypoglycemia symptoms: Sweating, trembling, dizziness, confusion, hunger, weakness — typically 15–60 min post-injection
– Muscle/joint pain and stiffness
– Headache
– Nausea
– Fatigue
– Water retention / mild edema

Less common:
– Jaw pain or facial bone changes (with prolonged high-dose use — acromegaly-like effects)
– Intestinal/abdominal discomfort: IGF-1 promotes intestinal cell growth; prolonged use may cause gut hypertrophy
– Paresthesia (tingling/numbness)

Serious/long-term:
– Cancer promotion: IGF-1 activates PI3K/Akt/mTOR — same pathways driving tumor growth. Elevated IGF-1 is epidemiologically linked to breast, prostate, and colorectal cancers.
– Organ growth: Prolonged high-dose use may cause abnormal growth of internal organs (intestines, colon, jaw) — acromegaly-like syndrome
– Receptor desensitization: Prolonged use decreases receptor responsiveness

Contraindications

No formal FDA contraindications (no approved label).

Based on pharmacology, animal data, and class effects:

Absolute avoid:
– Active malignancy or strong family/personal cancer history: IGF-1 receptor activation is a key proliferative signal in many cancers — most serious contraindication
– Athletes subject to WADA/USADA: Prohibited S2 — absolute contraindication
– Concurrent insulin use: Risk of life-threatening synergistic hypoglycemia
– Fasted state injection: Acute hypoglycemia risk — do not inject without food

Strong caution:
– Diabetes mellitus or insulin resistance: Already impaired glucose regulation; hypoglycemia and paradoxical hyperglycemia risk
– History of hypoglycemia episodes
– Pregnancy and breastfeeding: No safety data; IGF-1 promotes fetal growth — unpredictable effects
– Children with open epiphyses: Abnormal bone/tissue growth risk
– Cardiovascular disease: IGF-1 has cardiac remodeling effects — uncharacterized in context of supraphysiological levels
– Hypersensitivity to IGF-1 LR3 or excipients

Pharmacology

IGF-1 LR3 (Insulin-Like Growth Factor-1 Long R3) is a synthetic 83-amino acid modified analogue of human IGF-1. Compared to native IGF-1 (70 amino acids):

Modification 1 — Arginine substitution (R3):
Glu → Arg at position 3. This single amino acid change dramatically reduces binding to IGF-binding proteins (IGFBPs), particularly IGFBP-3.
Result: ~500–1,000-fold lower IGFBP affinity vs. native IGF-1
Consequence: Much larger free (unbound, biologically active) fraction circulating

Modification 2 — N-terminal Extension (Long):
13 additional amino acids (MFPAMPLLSLFVN) added at N-terminus
Further reduces IGFBP binding; improves metabolic stability

Net pharmacokinetic effect:
Native IGF-1: ~95% protein-bound in circulation; half-life ~15 minutes
IGF-1 LR3: Very low protein binding; half-life ~20–30 hours (40–120x longer active exposure)

This extended half-life and high free fraction are intentional design features for laboratory receptor signaling research — but they also substantially increase clinical risks for human use (especially hypoglycemia and prolonged IGF-1R stimulation).

MW: ~9,117 Daltons. Lyophilized powder; reconstituted with Bacteriostatic Water; stable 4 weeks refrigerated.

Mechanism of action

IGF-1 LR3 acts as a full agonist at the IGF-1 receptor (IGF-1R) with minimal IGFBP binding:

1. IGF-1 Receptor (IGF-1R) Activation (primary mechanism):
IGF-1R is a transmembrane tyrosine kinase receptor expressed on virtually all cell types.
Binding → receptor autophosphorylation → activation of two major downstream pathways:

a) PI3K/Akt/mTOR pathway:
→ Protein synthesis and muscle hypertrophy (activates ribosomal S6K1, 4E-BP1)
→ Anti-apoptotic signaling (promotes cell survival)
→ Glucose uptake (GLUT4 translocation) — basis for hypoglycemia risk
→ This is the same pathway driving tumor growth in many cancers

b) MAPK/ERK pathway:
→ Cell proliferation and differentiation
→ Muscle satellite cell activation and fusion

2. Insulin Receptor (IR) — weak cross-reactivity:
IGF1LR3 has weak but measurable binding to the insulin receptor
→ Acute glucose-lowering effect (similar to insulin but weaker)
→ Particularly significant in fasted state when combined with reduced IGFBP buffering

3. Reduced IGFBP buffering (key distinguishing factor):
In normal physiology, IGFBPs act as a reservoir and buffer — releasing IGF-1 slowly and preventing excessive receptor activation.
IGF-1 LR3 bypasses this buffer entirely → all circulating molecules are immediately bioavailable for receptor binding → more potent and prolonged effect than equivalent dose of native IGF-1.

4. Skeletal muscle specific effects:
– Increases muscle cell sensitivity to insulin (GLUT4 upregulation)
– Promotes satellite cell proliferation and myotube fusion (hypertrophy)
– Reduces fat storage within muscle cells

Result Claims from Different Companies

No major pharmaceutical company commercial claims (no approved drug).

Research and in vitro/animal data:

Human cell/tissue studies (not human RCTs):
– Human myotube studies: IGF-1 (including LR3 variant) increases fusion index, myonuclei number, and myosin heavy chain content — hallmarks of muscle hypertrophy at cellular level (Vita Bella Health, citing published cell studies)
– Human tendon-cell studies: Elevated collagen I and III expression following IGF-1 exposure — suggesting faster connective tissue healing potential

Animal and preclinical data:
– Rodent muscle hypertrophy models: IGF1LR3 produced significantly greater lean mass gains vs. native IGF-1 at equivalent doses due to extended half-life
– Wound healing models: Improved tissue repair and angiogenesis
– Neuroprotection: Neuronal survival support in TBI models

CRITICAL LIMITATIONS (stated by Peptide Catalog, 2026):
‘There are zero published human RCTs of IGF1LR3 for body composition. All claims rest on rodent data and on mecasermin (native IGF-1) trials, which used a different molecule.’

Safety data from fetal animal model:
– Sheep fetal infusion: High-dose IGF-1 LR3 induced severe hypoglycemia and hypoxemia — confirming potency and the risk of misuse in humans.

WADA prohibition status: IGF1LR3 is prohibited under S2 at all times in sport, reflecting its recognized potential for performance enhancement. The prohibition itself confirms the belief in efficacy — but this is not a substitute for clinical evidence of safety and efficacy in humans.

Disclaimer

This content about “IGF-1 LR3” is for informational and educational purposes only, is not medical advice, does not replace consultation with a licensed healthcare professional, and affiliate links may result in compensation at no additional cost to you.

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