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IGF-1 LR3

IGF-1 LR3 (Long Arginine 3 Insulin-like Growth Factor 1) is a synthetic, modified version of the naturally occurring hormone IGF-1. It is an 83-amino acid peptide that has been engineered to be more potent and longer lasting than the native hormone. The modifications are twofold. First, an arginine amino acid replaces a glutamic acid at position 3 (hence “Arginine 3”). Second, 13 additional amino acids are added at the N-terminus (hence “Long”). These structural changes dramatically alter its behavior in the body by reducing its affinity for insulin-like growth factor binding proteins (IGFBPs), allowing it to circulate in a much more active, unbound state. Natural IGF-1 is produced primarily in the liver in response to growth hormone stimulation. It circulates through the body bound to IGFBPs, which regulate its activity and limit its half-life to approximately 12 to 15 hours. IGF-1 LR3’s modifications give it very low affinity for these binding proteins, resulting in approximately 3 times greater potency than native IGF-1 and a significantly extended half-life of 20 to 30 hours. IGF-1 LR3 is used primarily in research settings to study growth and metabolism. It activates the same IGF-1 receptor (IGF-1R) as native IGF-1 and engages downstream signaling cascades including the PI3K/Akt and MAPK/ERK pathways, which regulate cellular proliferation, differentiation, survival, and metabolic signaling. The peptide also demonstrates limited cross- interaction with the insulin receptor. Recombinant production of IGF-1 LR3 is typically carried out using engineered protein expression systems in Escherichia coli. Following expression, chromatographic purification and refolding techniques are employed to obtain a correctly folded polypeptide suitable for experimental use.

Molecular Formula: C₄₀₀H₆₂₅N₁₁₁O₁₁₅S₉

Molecular Weight: 9,117.5 g/mol

Sequence: MFPAMPLSSL FVNGPRTLCG AELVDALQFV CGDRGFYFNK PTGYGSSSRR

APQTGIVDEC CFRSCDLRRL EMYCAPLKPA KSA

CAS Number: 946870-92-4

Synonyms: Long R3-IGF-1, LR3-IGF-1, Long Arg3 IGF-1

IGF-1 LR3 is not FDA-approved for any medical use. It has gained significant attention in performance and research circles for its powerful effects on muscle growth, recovery, and body composition.

How It Works

The IGF-1 Receptor Pathway

IGF-1 LR3 works by binding to and activating the IGF-1 receptor (IGF-1R), a transmembrane tyrosine kinase receptor found on cells throughout the body. When IGF-1 LR3 binds, the receptor undergoes autophosphorylation, which activates two major signaling pathways:

metabolic regulation.

differentiation. These pathways work together to produce IGF-1 LR3’s anabolic effects. Due to its reduced affinity for IGFBPs, IGF-1 LR3 demonstrates prolonged receptor availability in experimental systems, enabling extended pathway activation compared to native IGF-1.

Muscle Growth Mechanisms

IGF-1 LR3 promotes muscle growth through two distinct processes:

synthesis, positive nitrogen balance, and improved amino acid uptake.

form new muscle fibers. This is sometimes called “true hypertrophy” because it involves creating new cells rather than just enlarging existing ones. The hyperplasia effect sets IGF-1 apart from most anabolic compounds, which work only through hypertrophy. Satellite cell activation enables both the repair of damaged muscle and the formation of entirely new muscle fibers.

Myostatin Counteraction

Myostatin (growth differentiation factor 8) is a muscle protein that inhibits muscle growth and differentiation. In mouse models of Duchenne muscular dystrophy, IGF-1 LR3 and other IGF-1 derivatives have been shown to counteract the negative effects of myostatin, protecting muscle cells and preventing apoptosis. IGF-1 LR3 appears to work by activating MyoD, the protein normally activated by exercise or tissue damage that is responsible for muscle hypertrophy.

Extended Activity

Because IGF-1 LR3 has very low affinity for binding proteins, it remains active in circulation for 20 to 30 hours rather than being quickly sequestered and cleared. This extended activity window means each dose produces sustained effects on target tissues. In contrast, native IGF-1 circulates for only 12 to 15 hours, much of which is spent bound to IGFBPs in an inactive state.

Direct vs. Indirect Action

Unlike HGH, which works indirectly by stimulating the liver to produce IGF-1, IGF-1 LR3 acts directly on target tissues. It does not require conversion or processing by the liver. This direct action produces more consistent and predictable effects on growth factor signaling.

Somatostatin Feedback and Secretagogue Interference

IGF-1 LR3 raises circulating IGF-1 directly, which triggers somatostatin release from the hypothalamus. Somatostatin blocks the pituitary from responding to GH secretagogue signals. Research showed GHRH pathway compounds were inhibited by 86% and ghrelin pathway compounds were blunted by approximately 32% after exogenous GH injection. This means IGF- 1 LR3 should not be stacked with GH secretagogues (CJC-1295, Ipamorelin, Tesamorelin, MK- 677), as somatostatin prevents them from producing meaningful GH pulses. These are different tools for different goals: secretagogues work within the body’s natural feedback system, while IGF-1 LR3 bypasses it entirely.

Benefits

Muscle Cell Proliferation (Hyperplasia) IGF-1 LR3 activates satellite cells and promotes the formation of new muscle cells, not just the enlargement of existing ones. This unique mechanism can produce muscle growth beyond what is achievable through hypertrophy alone. Studies have shown this effect can occur at doses far lower than would be needed with native IGF-1.

Enhanced Muscle Growth (Hypertrophy) IGF-1 LR3 increases protein synthesis and creates a positive nitrogen balance. It enhances the uptake of amino acids into muscle cells and promotes the utilization of nutrients for muscle building. Users typically report fuller, denser muscles over time.

Accelerated Recovery

IGF-1 promotes tissue repair and regeneration. This translates to faster recovery between training sessions, reduced muscle soreness, and improved healing from minor injuries. The satellite cell activation also supports repair of damaged muscle tissue.

Fat Loss and Body Composition

IGF-1 LR3 improves nutrient partitioning, directing calories toward muscle tissue rather than fat storage. The peptide boosts fat metabolism indirectly by binding to both the IGF-1R receptor and the insulin receptor, increasing glucose uptake from the blood by muscle, nerve, and liver cells. This overall decrease in blood sugar levels triggers adipose tissue and the liver to break down glycogen and triglycerides.

Improved Insulin Sensitivity

IGF-1 has insulin-like effects and can improve glucose transport into muscle cells. Research shows IGF-1 can reduce insulin requirements by up to 10% in diabetic models. This supports better nutrient utilization and glycogen storage, particularly when combined with post-workout nutrition.

Connective Tissue Repair

Research suggests IGF-1 LR3 may accelerate healing of tendons, ligaments, and other connective tissues. This makes it of interest for injury recovery applications and musculoskeletal rehabilitation.

Anti-Aging Effects

IGF-1 levels decline with age, contributing to sarcopenia (age-related muscle loss). IGF-1 LR3 promotes tissue repair and maintenance throughout the body, making it a protective molecule against cell damage and the effects of aging. Research in animal models indicates IGF-1 LR3 administration may help offset the effects of cellular aging.

What the Science Shows

Research on IGF-1 LR3 specifically is limited to preclinical models, but extensive research exists on IGF-1 and its mechanisms that directly inform understanding of the LR3 analog.

Structural Modifications and Potency

The modifications that distinguish IGF-1 LR3 from native IGF-1 (arginine at position 3 and 13 additional N-terminal amino acids) result in:

Satellite Cell Activation (Adams, 2002) Research published in the Journal of Applied Physiology demonstrated that IGF-1 induces proliferation and differentiation of muscle satellite cells, enabling hypertrophic adaptations in response to mechanical overload. This autocrine/paracrine signaling mechanism supports the foundation for IGF-1 LR3’s effects on muscle growth through both hypertrophy and hyperplasia.

Protein Metabolism (Fryburg, 1994) Published in the American Journal of Physiology, this study showed that IGF-1 exerts growth hormone-like and insulin-like actions on human muscle protein metabolism, directly increasing protein synthesis and reducing protein breakdown in skeletal muscle tissue.

Myogenesis and Growth Factor Signaling (Florini et al., 1996) A comprehensive review in Endocrine Reviews documented the role of growth hormone and the insulin-like growth factor system in myogenesis, establishing the molecular mechanisms by which IGF-1 promotes muscle cell development, differentiation, and repair.

Myostatin Counteraction in Muscular Dystrophy Models

In mouse models of Duchenne muscular dystrophy, IGF-1 LR3 was found to counteract the negative effects of myostatin, protecting muscle cells from apoptosis and promoting regeneration through activation of the MyoD transcription factor.

Somatostatin Negative Feedback (Arvat et al., 1997) Published in Metabolism, this study demonstrated the mechanisms underlying negative GH autofeedback. After exogenous GH injection, GHRH pathway compounds were inhibited by 86% and ghrelin pathway compounds were blunted by approximately 32%. This established why IGF-1 LR3 should not be combined with GH secretagogues.

Metabolic Effects

Research has shown that IGF-1 can improve insulin sensitivity and reduce insulin requirements in diabetic patients by up to 10%. IGF-1 LR3’s extended activity and greater potency could enhance these metabolic benefits in experimental settings.

Bone Formation

Clinical data shows that IGF-1 stimulates bone formation through direct effects on osteoblasts. The anabolic activity and bone-protective effects of IGF-1 signaling have been documented across multiple research models.

Dosing Protocol

IGF-1 LR3 is typically dosed daily via subcutaneous injection. Due to its potency and the risk of hypoglycemia, careful dosing is essential. IGF-1 LR3 is not FDA-approved, and no standardized human dosing protocol exists.

Standard Protocol

Protocol Dose Frequency Duration Starting 20 to 30 mcg Daily Week 1 (assess tolerance) Standard 40 to 80 mcg Daily 4 to 6 weeks Maximum 100 mcg Daily Not for beginners

Cycle length: 4 to 6 weeks on, followed by 4 to 6 weeks off. Continuous use beyond 8 weeks increases the risk of receptor desensitization and insulin resistance.

Beginner Protocol

Training Day Protocol

Some users dose only on training days to maximize the anabolic window around exercise:

Timing Considerations

nutrient uptake.

Critical Dosing Notes

consume carbohydrates 15 to 30 minutes after injection to prevent blood sugar drops.

677 will be rendered ineffective due to somatostatin-mediated feedback suppression.

Draw Volumes by Vial Size

1 mg (1,000 mcg) Vial (1 mL reconstitution = 1,000 mcg/mL) Dose Volume Units on Syringe 20 mcg 0.02 mL 2 units 40 mcg 0.04 mL 4 units 50 mcg 0.05 mL 5 units 60 mcg 0.06 mL 6 units 80 mcg 0.08 mL 8 units 100 mcg 0.10 mL 10 units

Vial duration at 50 mcg/day: 20 days. 1 mg (1,000 mcg) Vial (0.5 mL reconstitution = 2,000 mcg/mL) Dose Volume Units on Syringe 20 mcg 0.01 mL 1 unit 40 mcg 0.02 mL 2 units 60 mcg 0.03 mL 3 units 80 mcg 0.04 mL 4 units 100 mcg 0.05 mL 5 units

Note: Very small volumes require precise syringes. Consider 1 mL reconstitution for easier measurement.

Reconstitution Instructions

Important: IGF-1 LR3 should be reconstituted with 0.6% acetic acid solution, not bacteriostatic water. IGF-1 LR3 is more stable at a lower pH. Bacteriostatic water can cause degradation and reduce potency. 1. Wipe the vial stopper and acetic acid vial with alcohol swabs. 2. Draw 0.5 to 1 mL of 0.6% acetic acid solution (based on desired concentration). 3. Insert the needle through the rubber stopper at an angle. 4. Let the acetic acid trickle down the inside wall of the vial slowly. Do not inject directly onto the powder. 5. Swirl gently until fully dissolved. Do not shake. 6. The solution should be clear. If cloudy or contains particles, do not use. 7. Label the vial with the date and concentration.

Side Effects and Cautions

Hypoglycemia (Most Important) IGF-1 LR3 has insulin-like effects and can drop blood sugar significantly. This is the most common and most dangerous acute side effect. Symptoms include:

Always have fast-acting carbohydrates available (glucose tablets, juice, candy). Many users consume carbohydrates 15 to 30 minutes after injection.

Other Common Side Effects

Long-Term Concerns

Signs to Stop or Reduce Dose

Contraindications and Precautions

Do Not Use If You Have

tumor growth)

Use Extreme Caution With

Drug Interactions

677. IGF-1 LR3 triggers somatostatin release, which blocks pituitary response to these compounds.

Combining with insulin is very dangerous and not recommended outside of highly supervised medical settings.

Important Monitoring

Comparison to Similar Compounds

Compound Type Half-Life Primary Use Action IGFBP

Binding

IGF-1 LR3 Synthetic IGF- 20 to 30 hours Systemic Direct Very low 1 analog growth Native IGF-1 Endogenous 12 to 15 hours Growth Direct High hormone regulation

IGF-1 DES Truncated 20 to 30 Localized Direct None IGF-1 analog minutes growth MGF Mechano 5 to 7 minutes Satellite cell Direct Low growth factor activation HGH Growth 3 to 5 hours Broad anabolic Indirect (via N/A hormone IGF-1)

IGF-1 LR3 is preferred for systemic, sustained anabolic effects. IGF-1 DES is used for localized, short-duration effects at specific muscle sites. MGF is used specifically for post-workout satellite cell activation. HGH works indirectly by stimulating the liver to produce IGF-1 and allows more natural feedback regulation.

Success Tips

Manage Hypoglycemia Risk

This is non-negotiable. Always have fast-acting carbohydrates available (glucose tablets, juice, candy). Many users intentionally consume carbohydrates 15 to 30 minutes after injection to prevent blood sugar drops. Never inject in a fasted state unless experienced.

Time Around Training

Post-workout is the most popular timing because muscle tissue is primed for growth and nutrient uptake. The anabolic signaling from training combines with IGF-1 LR3’s effects for maximum benefit.

Ensure Adequate Protein

IGF-1 LR3 enhances protein synthesis, but raw materials are required. Consume high-quality protein (0.8 to 1.0 grams per pound of body weight) throughout the day, with particular attention to post-workout nutrition.

Cycle Properly

Do not run IGF-1 LR3 continuously. The standard pattern is 4 to 6 weeks on followed by 4 to 6 weeks off. This prevents receptor desensitization and reduces the risk of insulin resistance.

Do Not Stack with Secretagogues

Do not run IGF-1 LR3 alongside GH secretagogues (CJC-1295, Ipamorelin, Tesamorelin, MK- 677). Elevated IGF-1 triggers somatostatin release, which blocks pituitary GH secretion. These are different tools for different goals. Choose one approach.

Start Low

Begin with 20 to 30 mcg daily to assess response and tolerance before increasing. IGF-1 LR3 is potent and individual responses vary significantly.

Foundation First

Peptides support growth and recovery. They do not replace the fundamentals: adequate sleep, stress management, whole food nutrition, progressive training, and consistent effort. An optimized foundation allows peptides to work more effectively.

Storage and Handling

Before Reconstitution

After Reconstitution

Legal Status

United States: IGF-1 LR3 is not FDA-approved for human use. It is classified as a research chemical. Distribution or marketing for bodybuilding or athletic use is illegal. WADA Status: IGF-1 and all analogs, including LR3, are prohibited substances under the S2 category (Peptide Hormones, Growth Factors, and Related Substances). Competitive Athletes: Do not use if subject to drug testing. International: Not approved for clinical use. Available for research purposes in most countries.

Frequently Asked Questions

Is IGF-1 LR3 more dangerous than HGH? IGF-1 LR3 carries different risks than HGH. The most immediate concern is hypoglycemia, which can be severe. Long-term concerns include potential for abnormal cell growth and insulin resistance. HGH works indirectly and allows more natural feedback regulation. IGF-1 LR3 is generally considered higher risk due to its direct, potent action.

Can IGF-1 LR3 cause cancer?

IGF-1 promotes cell growth and proliferation. In people with existing cancer, it may accelerate tumor growth. Large-scale studies have shown associations between elevated IGF-1 levels and certain cancers. This is why it is contraindicated in anyone with active cancer or a history of cancer. What is the difference between IGF-1 LR3 and IGF-1 DES? IGF-1 LR3 has a long half-life (20 to 30 hours) and produces systemic effects throughout the body. IGF-1 DES has a very short half-life (20 to 30 minutes) and is used for localized effects at specific muscle sites. LR3 is more commonly used for general muscle-building goals. How quickly will I see results? Enhanced recovery may be noticeable within the first week. Muscle fullness and growth typically become apparent at 2 to 4 weeks. Significant body composition changes develop over the full 4- to 6-week cycle. Should I inject into the muscle I am training? Unlike IGF-1 DES, which may have localized effects, IGF-1 LR3’s systemic activity means the injection site does not significantly affect which muscles benefit. Standard subcutaneous injection is appropriate. Can I use IGF-1 LR3 with HGH or secretagogues? No. IGF-1 LR3 raises circulating IGF-1 directly, triggering somatostatin release from the hypothalamus. Somatostatin blocks the pituitary from responding to GH secretagogue signals. Research showed GHRH pathway compounds were inhibited by 86% and ghrelin pathway compounds were blunted by approximately 32%. Running secretagogues alongside IGF-1 LR3 wastes their potential because somatostatin prevents them from producing meaningful GH pulses. Why does IGF-1 LR3 use acetic acid instead of bacteriostatic water? IGF-1 LR3 is more stable at a lower pH. Bacteriostatic water can cause degradation and reduce potency over time. The 0.6% acetic acid solution provides the pH environment the peptide needs to remain intact and effective throughout its shelf life after reconstitution.

References

1. Adams GR. Invited review: autocrine/paracrine IGF-I and skeletal muscle adaptation. Journal of Applied Physiology. 2002;93(3):1159–1167. 2. Fryburg DA. Insulin-like growth factor I exerts growth hormone- and insulin-like actions on human muscle protein metabolism. American Journal of Physiology. 1994;267(2):E331–E336. 3. Florini JR, Ewton DZ, Coolican SA. Growth hormone and the insulin-like growth factor system in myogenesis. Endocrine Reviews. 1996;17(5):481–517. 4. Arvat E, di Vito L, Broglio F, et al. Mechanisms underlying the negative growth hormone (GH) autofeedback on the GH-releasing effect of hexarelin in man. Metabolism. 1997;46(1):83– 88. 5. Yakar S, Rosen CJ, Beamer WG, et al. Circulating levels of IGF-1 directly regulate bone growth and density. Endocrine Reviews. 2001;22(6):803–817. 6. Bach LA, Headey SJ, Norton RS. IGF-binding proteins—the pieces are falling into place. Molecular and Cellular Endocrinology. 2018;473:1–9. 7. Tomas FM, Knowles SE, Owens PC, et al. Anabolic effects of insulin-like growth factor-I (IGF-I) and an IGF-I variant in normal female rats. Journal of Endocrinology. 1993;137(3):413– 421. 8. Mohan S, Baylink DJ. IGF-binding proteins are multifunctional and act via IGF-dependent and -independent mechanisms. Journal of Endocrinology. 2002;175(1):19–31. 9. Humbel RE. Insulin-like growth factors I and II. European Journal of Biochemistry. 1990;190(3):445–462.

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