IGF-1 LR3 Dosing Guide: Protocols (2026)

IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a modified analog of IGF-1 with significantly enhanced potency and a dramatically extended half-life. The modifications — an arginine substitution at position 3 and 13 additional N-terminal amino acids — reduce binding to IGF binding proteins (IGFBPs), allowing it to remain active in circulation for 20–30 hours compared to minutes for native IGF-1.

A potent anabolic agent with significant risks: IGF-1 LR3 is among the most powerful peptides used in the body composition community. It drives muscle growth through satellite cell activation and protein synthesis, but carries meaningful risks including hypoglycemia and theoretical cancer concerns. This is not medical advice.

Quick Reference: Community Dosing

Starting dose: 20 mcg daily for the first week. Experienced users: 40–50 mcg daily. Upper range: 80 mcg daily (split bilateral IM) — higher doses significantly increase side effect risk.

For GH secretagogue comparisons, see our MK-677 dosing guide and Ipamorelin dosing guide.

Loading vs Maintenance

IGF-1 LR3 requires careful dose titration due to its potency:

Week 1 (Titration): Start at 20 mcg daily. Monitor for hypoglycemia (dizziness, shakiness, sweating). Have fast-acting carbohydrates available.

Weeks 2–6 (Working dose): Increase to 40–50 mcg daily if well-tolerated. Some advanced users go to 60–80 mcg split bilaterally.

Cycling is critical: 4–6 weeks maximum, then equal time off. Extended use risks IGF-1 receptor desensitization, organ growth, and other complications.

Timing Considerations

• Post-workout injection: The most common timing — inject immediately after training to maximize nutrient partitioning and muscle uptake
• Have carbs ready: Consume carbohydrates shortly after injection to prevent hypoglycemia
• Training days preferred: Some protocols only use IGF-1 LR3 on training days (4–5x/week)
• Morning on rest days: If dosing daily, inject in the morning on rest days with a meal

Routes of Administration

Subcutaneous Injection

Provides systemic IGF-1 LR3 distribution throughout the body:

• Injection sites: Abdomen, love handles — standard SC areas
• Volume: Typically 0.1–0.2 mL
• Reconstitution: Add 1 mL bacteriostatic water to a 1 mg vial (1,000 mcg/mL). 50 mcg = 5 units on insulin syringe.
• Advantage: Consistent absorption, easier injection
• Consideration: Systemic effects may include unwanted organ/tissue growth

Intramuscular Injection

Targets IGF-1 LR3 delivery to specific muscle groups — the preferred route in bodybuilding communities:

• Injection sites: Biceps, deltoids, quads — inject into muscles trained that day
• Bilateral splitting: Divide dose between left/right of same muscle group
• Volume: Small volume, 0.1–0.2 mL with insulin syringe (29–31 gauge)
• Advantage: Theoretical local muscle growth enhancement
• Consideration: Site-specific growth enhancement is debated in the literature

Reconstitution Notes

IGF-1 LR3 requires careful handling:

• Acetic acid reconstitution: Some protocols use 0.6% acetic acid instead of bacteriostatic water for improved stability
• Gentle mixing: Swirl gently — never shake, as IGF-1 LR3 is fragile
• Refrigerate immediately: Store at 2–8°C, use within 28 days
• Do not freeze reconstituted solution

Where These Numbers Come From: Clinical Context

IGF-1 LR3 is a research tool and performance compound — it does not have human clinical trial data for the way it's used in the community.

Foundational IGF-1 Research

• Satellite cell activation — IGF-1 induces muscle hypertrophy through a combination of satellite cell activation and increased protein synthesis in differentiated myofibers (Adams & McCue, 1998)
• Organ growth in animal models — LR3 IGF-1 infusion stimulates organ growth (adrenals, gut, kidneys, spleen) while suppressing endogenous IGF-1 and IGFBP levels (Bastian et al., 1993)
• Muscle metabolism — IGF-1 plays central roles in muscle metabolism, protein synthesis, and myogenic differentiation through PI3K/Akt/mTOR signaling (Florini et al., 1996)

Why LR3 vs Native IGF-1

The LR3 modification provides:

1. 20–30 hour half-life vs minutes for native IGF-1
2. Reduced IGFBP binding — circulates mostly free/unbound
3. ~2–3x potency compared to native IGF-1 in bioassays
4. Sustained receptor activation — longer exposure to IGF-1R signaling

Community Dosing Derivation

Doses of 20–80 mcg daily are derived from:

1. Animal research scaling — Extrapolation from animal infusion studies
2. Bodybuilding community experience — Decades of underground use
3. Potency considerations — LR3's enhanced potency requires lower absolute doses than native IGF-1
4. Risk management — Balancing anabolic effects against hypoglycemia and growth concerns

Mechanism of Action

IGF-1 LR3 drives muscle growth through multiple anabolic pathways:

PI3K/Akt/mTOR signaling — IGF-1 LR3 binds the IGF-1 receptor (IGF-1R), activating IRS-1 → PI3K → Akt → mTORC1. This cascade directly stimulates ribosomal protein synthesis, the primary driver of muscle hypertrophy.

Satellite cell activation — IGF-1 is a potent activator of muscle satellite (stem) cells, promoting their proliferation, differentiation, and fusion into existing myofibers. This increases muscle fiber nuclei, enabling greater protein synthesis capacity (Adams & McCue, 1998).

Anti-catabolic effects — Akt activation by IGF-1 inhibits FoxO transcription factors, suppressing the ubiquitin-proteasome system (MuRF-1, MAFbx/Atrogin-1) responsible for muscle protein degradation.

Nutrient partitioning — IGF-1 LR3 promotes glucose uptake into muscle cells (similar to insulin), directing nutrients toward muscle tissue rather than fat storage. This also explains the hypoglycemia risk.

Reduced IGFBP sequestration — The LR3 modification means most of the peptide circulates in free/active form rather than being bound and inactivated by IGF binding proteins (Bastian et al., 1993).

Hyperplasia potential — Unlike most anabolic agents that only cause hypertrophy (existing fiber enlargement), IGF-1 may promote hyperplasia (new muscle fiber formation) through satellite cell activation, though this remains debated.

Side Effects & Safety

⚠️ IGF-1 LR3 carries more significant risks than most peptides. This is not a beginner compound.

Acute Risks

Hypoglycemia (most immediate risk):

• IGF-1 LR3 promotes glucose uptake similar to insulin
• Symptoms: shaking, dizziness, sweating, confusion, fainting
• Prevention: Have fast-acting carbs available, inject with/before meals
• This can be dangerous — start at low doses

Short-Term Side Effects

• Jaw and hand growth — Chronic use can cause subtle acromegaly-like changes
• Gut distension — Organ growth with prolonged, high-dose use
• Joint pain — Connective tissue changes, water retention
• Fatigue/lethargy — Common, especially initially
• Injection site pain — Particularly with IM injections

Long-Term Concerns

• Cancer risk — Chronically elevated IGF-1 is associated with increased cancer risk in epidemiological studies. This is the most serious theoretical concern.
• Organ enlargement — Heart, intestines, and other organs express IGF-1 receptors
• Cardiomegaly — Potential heart enlargement with chronic supraphysiological IGF-1 levels
• IGF-1 receptor desensitization — Extended use may reduce receptor sensitivity

Critical Safety Rules

1. Always have fast-acting glucose available during and after injection
2. Never inject before sleep — hypoglycemia during sleep is dangerous
3. Cycle strictly — 4–6 weeks maximum
4. Monitor blood glucose — Regular testing recommended
5. Get blood work — IGF-1 levels, fasting glucose, insulin, HbA1c

Stacking IGF-1 LR3

IGF-1 LR3 is typically used in advanced stacking protocols:

IGF-1 LR3 + MK-677 (Growth Stack)

Combines exogenous IGF-1 with GH secretion:

• IGF-1 LR3 → direct IGF-1R activation, satellite cell stimulation
• MK-677 → GH secretion, appetite increase, sleep quality

IGF-1 LR3 + BPC-157 (Growth + Recovery)

For muscle growth with joint and tissue support:

• IGF-1 LR3 → anabolic drive, protein synthesis
• BPC-157 → tendon/ligament healing, anti-inflammatory

IGF-1 LR3 + CJC-1295/Ipamorelin

For comprehensive GH/IGF-1 axis stimulation:

• IGF-1 LR3 → direct IGF-1R activation
• CJC-1295/Ipamorelin → pulsatile GH release

Stacking Considerations

• Start IGF-1 LR3 alone first — Assess tolerance before adding compounds
• Watch blood sugar closely — Multiple compounds may compound hypoglycemia risk
• Lower IGF-1 LR3 doses when stacking — 20–30 mcg rather than 50+ mcg
• Blood work is essential — Monitor IGF-1, glucose, insulin regularly

Frequently Asked Questions

What is the standard IGF-1 LR3 dose?

20–50 mcg subcutaneously or intramuscularly once daily. Beginners start at 20 mcg; experienced users go up to 50–80 mcg. Higher doses significantly increase side effect risk.

What is the difference between IGF-1 and IGF-1 LR3?

IGF-1 LR3 has an arginine substitution at position 3 and 13 extra N-terminal amino acids, reducing IGFBP binding. This extends half-life from minutes to 20–30 hours and increases in vivo potency.

Should IGF-1 LR3 be injected subcutaneously or intramuscularly?

Both work. SC provides systemic distribution; IM (into trained muscles post-workout) is theorized to enhance local growth, though site-specific enhancement is debated.

How long should an IGF-1 LR3 cycle last?

4–6 weeks on, 4–6 weeks off. Cycling prevents receptor desensitization and manages risks from prolonged growth factor elevation.

What are the risks of IGF-1 LR3?

Hypoglycemia (most immediate), potential organ growth with chronic use, theoretical cancer risk from prolonged IGF-1 elevation, and connective tissue changes. This is a higher-risk peptide.

Can IGF-1 LR3 be stacked with growth hormone?

Yes, but this is advanced and risky. GH raises endogenous IGF-1, so adding exogenous LR3 creates supraphysiological levels. Use lower LR3 doses (20 mcg) if combining. Blood work is mandatory.

Related Guides

• MK-677 Dosing Guide — Oral GH secretagogue for stacking
• Ipamorelin Dosing Guide — GH secretagogue with clean release profile
• BPC-157 Dosing Guide — Recovery peptide to complement anabolic protocols
• Peptide Stacking Guide — Principles for combining growth peptides

References

For educational and research purposes only. This is not medical advice. IGF-1 LR3 is a research compound with no FDA approval. It carries significant risks including hypoglycemia and theoretical cancer concerns. All protocols described are for informational purposes.