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IGF-1 LR3

Last reviewed: April 18, 2026 by The Peptide Catalog Team

A powerful anabolic peptide for lean muscle growth and enhanced recovery. IGF-1 LR3 is a modified version of insulin-like growth factor 1 with an extended half-life (~20-30 hours vs minutes). The modifications make it more potent for muscle protein synthesis and less affected by IGF binding proteins. Used in research for muscle growth and recovery.

CategoryGrowth & Repair Peptides
ClassGH secretagogue
GoalMuscle Growth
Overview

Core Benefits

Key Advantages
Lean tissue growth
Direct muscle protein synthesis without going through GH.
Long-acting IGF analog
20–30 hour half-life vs. minutes for native IGF-1.
Local muscle effects
Used responsibly for site-specific muscle work.
Faster recovery
Speeds recovery from training and minor injuries.
Nutrient partitioning
Pushes nutrients toward muscle over fat.
Reduced binding
Less affected by IGF binding proteins — higher bioavailability.

These are educational summaries of commonly discussed effects in wellness/regenerative contexts, not guarantees.

IGF-1 LR3 Results Timeline

Progression
1
Day 1–3
Physical Changes
Enhanced muscle pump, initial fullness
Performance & Recovery
Improved recovery between sessions
Other Benefits
Possible hypoglycemia if not eating properly
2
Day 4–6
Physical Changes
Visible muscle growth, increased vascularity
Performance & Recovery
Enhanced strength and endurance
Other Benefits
Faster healing of minor injuries
3
Day 7–10
Physical Changes
Peak anabolic effects, significant lean mass gains
Performance & Recovery
Peak strength and recovery
Other Benefits
Enhanced nutrient partitioning
4
Post-Cycle
Physical Changes
Gains maintained with proper training/nutrition
Performance & Recovery
Sustained benefits during 4-week off period
Other Benefits
10 days on, 4 weeks off cycling recommended

Timeline is illustrative and non-guaranteed. Outcomes vary and are commonly discussed alongside training, nutrition, sleep, and cycling practices.

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Evidence at a glance

Two parallel grades per outcome — clinical RCT depth and real-world community adoption. See the Research Overview below for citations and detail.

OutcomeClinical EvidenceCommunity Evidence
Anabolic effects in animal modelsModerateModerate
Muscle protein synthesis / lean massPreliminaryModerate
Glucose / hypoglycemia riskStrongModerate
Body composition in healthy adultsPreliminaryModerate
How It WorksGrowth Factor — Long-Acting IGF-1 Analog

Receptor → Growth Cascade → Anabolic Signaling → Outcomes

1
Target

IGF-1 Receptor (IGF-1R) — Direct Activation

Unlike GH peptides that indirectly raise IGF-1 by stimulating GH release, IGF-1 LR3 directly activates IGF-1 receptors. The LR3 modification (Arg→Glu at position 3 + 13-AA extension) reduces binding to IGF binding proteins, keeping it active ~3x longer than native IGF-1.

2
Cellular Signal

PI3K/Akt + MAPK → Protein Synthesis + Cell Proliferation

Direct IGF-1R activation triggers two major cascades: PI3K/Akt (protein synthesis, anti-apoptosis) and MAPK/ERK (cell proliferation, differentiation). This is the terminal growth signal that GH peptides ultimately produce, but IGF-1 LR3 bypasses the GH intermediate entirely.

3
Systemic Effect

Direct Anabolic Signaling → Muscle Hypertrophy

Potent anabolic effects: increased protein synthesis, muscle cell proliferation (hyperplasia — new fibers, not just bigger ones), nutrient partitioning toward muscle. Also lowers blood sugar by driving glucose into muscle cells — monitor blood sugar carefully.

4
What You Notice

Muscle Fullness → Rapid Recovery → Hypoglycemia Risk

Noticeable muscle fullness and pump within days. Accelerated recovery between sessions. Risk of hypoglycemia (low blood sugar) is real and requires careful monitoring. This is a potent compound — not for beginners.

What Makes This Peptide Different

IGF-1 LR3 is unique in bypassing GH entirelyto directly activate growth signaling. While CJC-1295 and Ipamorelin stimulate GH → IGF-1 naturally, IGF-1 LR3 delivers the end-product directly. This makes it more potent but also more risky — it affects blood sugar, doesn't have the natural feedback loops of GH peptides, and requires careful dosing and monitoring.

Research overview

Outcome-by-outcome look at what the evidence actually supports for IGF-1 LR3, including human vs. animal study counts and our editorial take on each.

Anabolic effects in animal models

Clinical:ModerateCommunity:Moderate

Tomas and colleagues published a series of CSIRO studies in the early 1990s showing LR3-IGF-I is approximately 2.5-fold more potent than native IGF-I in rat anabolism — increased body weight, organ growth, and feed efficiency under both freely-fed and food-restricted conditions. The potency advantage comes from poor IGFBP binding, leading to higher free IGF-I activity.

0 human studies · 12 animal studies

Key findings & citations
  • LR3-IGF-I is ~2.5-fold more potent than native IGF-I in rat anabolism (Tomas 1992).
  • Half-life extended to 20-30 hours via reduced IGFBP affinity.
  • Anabolic in dexamethasone-catabolic rats (preserves muscle mass under steroid stress).
  • Reduces plasma IGF-1 in continuous infusion via negative feedback.

Our take

The animal data is consistent and well-powered. Translation to humans rests on the recombinant IGF-1 (mecasermin) literature, which is a different molecule.

Body composition / hypertrophy in healthy adults

Clinical:PreliminaryCommunity:Moderate

There is no published human RCT of IGF-1 LR3 for muscle hypertrophy or body composition. All community use rests on rodent data and on the mecasermin (recombinant IGF-1) clinical literature in pediatric short stature and ALS — which used native IGF-1, not LR3.

0 human studies · 6 animal studies

Key findings & citations
  • Zero published human composition RCTs of IGF-1 LR3.
  • Mecasermin (native IGF-1, FDA-approved) demonstrates GH-axis-independent growth in pediatric patients.
  • Hypoglycemia risk is real and dose-dependent in mecasermin trials.

Our take

The animal anabolism is real. The human composition data isn't there. Anyone selling LR3 as a muscle-building peptide is selling extrapolation.

Hypoglycemia and metabolic risk

Clinical:StrongCommunity:Moderate

IGF-1 LR3 binds the insulin receptor with weak but real affinity, and mecasermin clinical trials documented hypoglycemia as a dose-limiting side effect. The LR3 variant escapes IGFBP binding, raising free-IGF activity even further — a known liability for users not eating before injection.

0 human studies · 4 animal studies

Key findings & citations
  • Mecasermin (native IGF-1) hypoglycemia rates ~50% in pediatric populations.
  • LR3 variant has higher free fraction, theoretically higher hypoglycemia risk.
  • Inappropriate timing (fasted state, alcohol, alongside insulin) compounds risk.

Our take

If hypoglycemia is the side effect, eat before you inject. The pharmacology is unforgiving on this point.

What IGF-1 LR3 doesn't do

Claims that current evidence does not support. Worth knowing before you set expectations.

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Dosing ProtocolMuscle Building

Educational reference only. Individual responses vary. Consult healthcare provider before use.

Vial Size
1 mg
Reconstitution
1 ml BAC water
Dose
50 mcg (5 units on 1ml syringe)
Timing
AM
Frequency
10 days in a row
Duration
10 days on, 4 weeks off
Protocol Notes
Very potent. Monitor blood sugar. Receptor desensitization can occur with prolonged use — keep cycles short.

Why This Dosing Protocol

Why post-workout? Muscle tissue is most receptive to IGF-1 signaling after training. Post-workout intramuscular injection targets growth to trained muscles.

Why 10 days on, 4 weeks off? IGF-1R can desensitize with continuous exposure. Short cycles preserve receptor sensitivity. The 4-week off period allows full receptor recovery.

Why monitor blood sugar? IGF-1 LR3 drives glucose into cells, which can cause hypoglycemia. Have fast-acting carbs available, especially during initial use.
Full Dosing GuideReconstitution CalculatorCycle Cost Calculator

Reconstitution Calculator

Dilution math and unit conversions. Prefilled using a common vial size for this peptide.

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Storage & Handling

Storage at a glance

Proper storage temperatures, shelf life, reconstitution best practices, and travel tips for lyophilized and reconstituted peptides.

Powder: Freezer
1+ year at -20°C
Reconstituted: Fridge
4 weeks max at 2-8°C
View Complete Storage Guide

Handling specifics

Educational overview on storage, labeling, and traceability considerations for lab environments. Consult primary literature and vendor documentation for specifics.

Powder storage (very stable)
  • Freezer (-20°C): 1+ year
  • Refrigerator (2-8°C): 1-3 months
  • Room temperature: 2-3 weeks (emergency only)
Reconstituted storage (fragile)
  • MUST refrigerate at 2-8°C
  • 4-week maximum shelf life
  • NEVER freeze after reconstitution
  • Use bacteriostatic water for multi-dose
Molecular Structure

IGF-1 LR3 sequence

Click any residue to see its properties.

HydrophobicPolarAcidic (−)Basic (+)Special

Sequence-derived properties

Length
83 residues
Molecular weight
9117.6 Da
backbone only
Avg hydrophobicity
-0.07
Kyte–Doolittle scale

Residue classes

Hydrophobic: 29 (35%)Polar: 17 (20%)Acidic (−): 7 (8%)Basic (+): 10 (12%)Special: 20 (24%)

Net charge distribution

Positive10 (12%)
Neutral66 (80%)
Negative7 (8%)

Amino acid frequency

L×8A×7G×7P×7R×7S×7C×6F×6D×4V×4

Modifications

  • Long R3 variant — Arg at position 3 + 13-residue N-terminal extension for reduced IGFBP binding

Sequence and properties provided for educational reference. Not for clinical dosing decisions.

  • Length: 83 amino acids
    (Native IGF-1 (70 AA) + 13 AA extension.)
  • Half-life: 20-30 hours
    (vs. minutes for native IGF-1.)
  • Binding: Reduced IGFBP
    (Less affected by binding proteins.)
  • Primary Use: Muscle growth
    (Direct anabolic effects.)
Key modifications
Arg³ substitution + 13 AA N-terminal extension
The modifications prevent IGF-1 LR3 from binding to IGF binding proteins (IGFBPs), leaving more free IGF-1 available for receptor activation and anabolic effects.
Key takeaway: IGF-1 LR3 provides direct anabolic signaling, bypassing the GH → IGF-1 pathway. More potent than native IGF-1 due to extended half-life and reduced binding protein interaction. Requires careful attention to blood sugar management.

FAQ

What makes IGF-1 LR3 different from regular IGF-1?

IGF-1 LR3 has an arginine substitution and a 13-amino acid extension that makes it less affected by IGF binding proteins. This extends its half-life from minutes to 20-30 hours and increases its potency for muscle protein synthesis compared to native IGF-1.

How does IGF-1 LR3 relate to growth hormone?

IGF-1 is the downstream mediator of many GH effects. When GH stimulates the liver, it produces IGF-1. IGF-1 LR3 bypasses this pathway, directly providing IGF-1 activity. It's more targeted for muscle growth but lacks the broader metabolic effects of GH itself.

What does IGF-1 LR3 do for muscle growth?

IGF-1 LR3 promotes muscle growth through multiple mechanisms: increasing protein synthesis, enhancing nitrogen retention, promoting satellite cell activation (muscle cell precursors), and potentially causing muscle hyperplasia (new muscle cell formation). It's one of the most potent peptides for anabolic effects.

What is the typical IGF-1 LR3 dosage?

A common research dosage is 50 mcg per day (5 units on 1ml syringe), administered in the AM. Protocol: 10 days in a row, then 4 weeks off. Keep cycles short due to receptor desensitization concerns. Monitor blood sugar.

What are the side effects of IGF-1 LR3?

Potential side effects include hypoglycemia (low blood sugar), joint pain, water retention, and gut growth with prolonged high-dose use. Some report headaches and lethargy. Because IGF-1 promotes cell growth broadly, there are theoretical concerns about tumor promotion, though evidence is limited.

Does IGF-1 LR3 cause hypoglycemia?

Yes, IGF-1 LR3 can cause hypoglycemia because IGF-1 has insulin-like effects on glucose uptake. This is why it's often taken with food or post-workout when glucose is being utilized. Users should monitor for symptoms like shakiness, sweating, and confusion.

Can IGF-1 LR3 be combined with GH peptides?

Yes, some combine IGF-1 LR3 with GH-releasing peptides, though this is considered an advanced approach. The theory is that GH peptides provide broader benefits while IGF-1 LR3 adds targeted anabolic effects. However, this increases complexity and potential side effects.

Why are IGF-1 LR3 cycles kept short?

Extended IGF-1 LR3 use can cause receptor desensitization, reducing effectiveness. It may also cause unwanted growth of organs (particularly intestines) and other tissues with prolonged high-dose use. Most protocols limit cycles to 4-6 weeks with equal time off between cycles.

How long does reconstituted peptide last?

Once mixed with bacteriostatic water, peptides remain stable for up to 4 weeks when refrigerated at 2-8°C (36-46°F). Unopened powder can last 1+ year in the freezer. Get our complete Storage & Travel Guide.

Is this peptide legal to purchase?

Peptides sold "for research purposes only" are legal to purchase in the US, but are not FDA-approved for human use outside of specific medical applications. Always consult a healthcare provider before use.

New to peptides?

Take our Peptide Match tool to find the best peptide for your goals. You can also read our Complete Guide to Peptides to learn the basics.

Scientific Sources

The following peer-reviewed studies and official resources provide additional scientific context for this peptide:

IGF-1 LR3 Research Articles

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Buy IGF-1 LR3: Compare 3 Vendors, From $59.96

Compare 3 IGF-1 LR3 vendors side by side: from $59.96 a vial, best value $59.96/mg. Codes save up to 25%. Vial sizes, COA status, real cost per week.

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Disclosure: we may earn affiliate commission from qualifying purchases. Educational information only — not medical advice.