IGF-1 LR3
A long-acting synthetic IGF-1 analog engineered to escape binding-protein control and drive sustained, supraphysiologic IGF-1 receptor signaling for muscle growth.
IGF-1 LR3 is an 83-amino-acid analog of insulin-like growth factor 1 built from the native 70-residue sequence plus a 13-amino-acid N-terminal extension and an arginine substitution at position 3. These changes sharply reduce binding to IGF-binding proteins (especially IGFBP-3), extending serum half-life from roughly 12 minutes for native IGF-1 to 20-30 hours and raising the free, bioactive fraction. It directly activates the IGF-1 receptor downstream of the pituitary GH axis. Originally a cell-culture reagent, it has no FDA-approved human indication and is sold research-use-only; its potent anabolic signal is inseparable from hypoglycemia and long-term cancer-risk concerns.
Class
Modified recombinant human IGF-1 analog (83 amino acids)
Half-life
20-30 hours
Routes
Subcutaneous, Intramuscular
Category
Growth Hormone & Performance
Researched benefits
What it's studied for
Muscle protein synthesis and hypertrophy
IGF-1 LR3 activates the IGF-1 receptor and its PI3K/Akt/mTOR cascade, driving ribosomal S6K1/4E-BP1 phosphorylation, increased muscle protein synthesis, and fiber hypertrophy. The anabolic effect is well-supported mechanistically and reported in rodent muscle models, though no human performance trials exist.
Satellite cell activation and tissue repair
Preclinical studies show robust satellite cell proliferation and tissue repair, mediated partly through the Ras/MAPK proliferative pathway. Sustained receptor signaling supports recovery and reduced workout-to-workout soreness in community use.
Extended, sustained IGF-1 signaling
By reducing IGFBP affinity (roughly 60% lower IGFBP-3 binding and near-abolished IGFBP-1 binding), a larger free fraction circulates and the half-life stretches to 20-30 hours, giving continuous receptor activation from once-daily dosing rather than the brief spikes of native IGF-1.
Enhanced glucose uptake and fat metabolism
Modest insulin-receptor cross-reactivity (~1-10% of IGF1R affinity) drives glucose disposal into muscle and adipose tissue and contributes to lipolysis, improving nutrient partitioning during training — the same property that creates hypoglycemia risk.
Amplified potency per dose
Escaping the IGFBP buffer means a small dose produces disproportionately large biological effects, with roughly 3-10x higher bioactive tissue concentration than equimolar native IGF-1.
Mechanism
How it works
IGF-1 LR3 binds the IGF-1 receptor (IGF1R), a receptor tyrosine kinase expressed on virtually every cell type. Ligand binding triggers IGF1R autophosphorylation and recruitment of IRS-1/2 adapters, activating the PI3K/Akt/mTOR pathway (the primary anabolic route that increases muscle protein synthesis, satellite cell proliferation, and fiber hypertrophy) and the Ras/Raf/MEK/ERK/MAPK pathway (driving cell-cycle progression, proliferation, and differentiation). The combination of strong mTOR activation and moderate proliferative signaling underlies both its muscle-building potency and the theoretical cancer-promotion and peripheral tissue-growth concerns.
The molecule's defining feature is escape from binding-protein control. Native IGF-1 circulates at 150-300 ng/mL but is 95-99% bound to IGFBP-3 and other IGFBPs in a biologically inactive reservoir released slowly by proteases such as PAPP-A. The 13-amino-acid N-terminal extension and the Arg3 substitution reduce IGFBP-3 affinity by roughly 60% and nearly abolish IGFBP-1 binding, raising the free fraction from ~1-2% to ~10-30% and extending serum half-life from ~12 minutes to 20-30 hours. The result is sustained, supraphysiologic free IGF-1 that bypasses the buffer system evolution built to keep IGF-1 signaling controlled.
IGF-1 LR3 acts downstream of the pituitary GH axis. Unlike GHRH analogs (which act at the pituitary GHRH receptor) or GHRPs (which act at the ghrelin receptor GHS-R1a), it directly activates peripheral IGF-1 receptors without requiring pituitary function and is not subject to pulsatile feedback regulation. Peak serum concentrations occur 2-6 hours after subcutaneous injection with elevation sustained beyond 24 hours, permitting once-daily dosing.
Because IGF1R is ubiquitous, sustained high-dose exposure grows any receptor-bearing tissue — including intestinal epithelium (the characteristic 'IGF gut' from gut hypertrophy), liver, spleen, kidneys, cardiac muscle, and connective tissue. Modest insulin-receptor cross-reactivity additionally drives glucose uptake, making post-injection hypoglycemia the primary acute safety concern.
Dosing protocols
Dosing & administration
Dosing reflects protocols reported in research and community literature for educational purposes. It is not medical advice or a recommendation. Most peptides here are not approved for human use.
Reconstitution
IGF-1 LR3 typically ships as 1 mg lyophilized powder and is unusual in often requiring dilute acetic acid rather than plain bacteriostatic water for stability — follow supplier instructions precisely. Most-stable approach: 0.6% acetic acid (or 0.05M) at 1 mg + 1 mL = 1 mg/mL, refrigerated immediately (stable ~30 days). Alternative: 1 mg + 1 mL BAC water = 1 mg/mL, less stable (use within 14-21 days). At 1 mg/mL, 20 mcg = 0.02 mL = 2 units on a U-100 insulin syringe; many users dilute to 1 mg + 2 mL = 500 mcg/mL so 20 mcg = 4 units for easier measurement. Do not shake (gently swirl); never freeze; protect from light. Store lyophilized at 2-8C (stable 1-2 years).
Beginner
- Dose
- 20 mcg
- Frequency
- Once daily
- Timing
- Morning with a high-carb breakfast, or post-workout, always with 30-40g fast-digesting carbohydrate within 30 minutes of injection
- Duration
- 4 weeks on / 4 weeks off
- Route
- Subcutaneous
Never inject fasted. Have fast carbs (juice, glucose tabs) on hand and test blood glucose at 30/60/90 min for the first 3-5 doses. Run baseline IGF-1, fasting insulin/glucose/HbA1c, CMP and CBC before starting.
Intermediate
- Dose
- 30-50 mcg
- Frequency
- Once daily
- Timing
- Post-workout on training days, morning with breakfast on rest days
- Duration
- 4-6 weeks on / 2-4 weeks off
- Route
- Subcutaneous
Cycle to limit cumulative peripheral tissue growth and cancer-mechanism exposure and to re-establish hypoglycemia tolerance. Monitor weekly fasting glucose/insulin; check IGF-1, CBC, CMP at weeks 4 and 8. Do not combine with exogenous insulin.
Advanced
- Dose
- 50-80 mcg
- Frequency
- Once daily
- Timing
- Post-workout with periworkout carbohydrate, in a caloric surplus
- Duration
- 4-6 weeks on / 4 weeks off; never exceed 8 consecutive weeks
- Route
- Subcutaneous
Reserved for experienced users with full risk awareness, often stacked with other anabolics and GH-axis support. Requires annual comprehensive physical with abdominal imaging, semi-annual IGF-1 trend monitoring, and colonoscopy after age 40 (or earlier with family history).
Site-targeted (advanced only)
- Dose
- 10-20 mcg per side
- Frequency
- Per workout
- Timing
- Bilateral injection into the trained muscle belly immediately post-training
- Duration
- Per workout session
- Route
- Intramuscular
Aims for high local tissue concentration and targeted hypertrophy (anecdotal, not validated in trials). Increases total IGF-1 exposure per session and raises hypoglycemia and injection-site soreness risk versus a single SC dose.
- Typical range is 20-100 mcg/day; weight-based guidance is 0.5-1 mcg/kg/day, not to exceed 100 mcg/day.
- The single most important rule: always dose with 30-40g fast-digesting carbohydrate within 30 minutes of injection. Never dose fasted, in a caloric deficit, or on aggressive carbohydrate restriction.
- Never combine with exogenous insulin, sulfonylureas, or meglitinides — compounded hypoglycemia can be life-threatening. Do not combine with mecasermin (redundant IGF1R activation).
- Cycle strictly (4-6 weeks on, 2-4 week washout minimum) and never exceed 8 consecutive weeks.
- Monitor cancer-risk signals: baseline and periodic labs, PSA in men over 40, abdominal palpation/imaging for longer-term use, and age-appropriate cancer screening.
- Discontinue immediately for any new or growing skin lesion, mass or lymphadenopathy, unexplained weight loss, symptomatic abdominal distension, persistent fasting glucose >110 mg/dL despite carb management, new cardiovascular symptoms, or acromegalic facial/extremity changes.
Evidence
Research & clinical studies (2)
Insulin-like growth factor (IGF)-I, IGF binding protein-3, and cancer risk: systematic review and meta-regression analysis
Renehan and colleagues found that high circulating IGF-1 concentrations are associated with increased risk of prostate, premenopausal breast, and colorectal cancers, establishing elevated IGF-1 as a well-characterized cancer risk signal.
Plasma insulin-like growth factor-I and prostate cancer risk: a prospective study
Chan and colleagues reported that men with higher plasma IGF-1 levels had a substantially increased risk of prostate cancer, linking the IGF-1 axis to malignancy in a prospective human cohort.
Combinations
Stacking & blends
Classical anabolic stack
Maximum muscle hypertrophy
Testosterone drives protein synthesis through androgen-receptor signaling while IGF-1 LR3 works through IGF1R/PI3K/mTOR, giving additive hypertrophic effect — but combined cancer, cardiac, and metabolic risks stack and warrant specialist supervision.
Anabolic intensification with GH-axis support
Combine direct IGF1R activation with endogenous, pulsatile GH/IGF-1 production
GHRH + GHS peptides drive native IGF-1 at physiologic, IGFBP-regulated levels alongside LR3's supraphysiologic free IGF-1; the counterargument is that stacking mechanisms compounds the theoretical cancer-risk signal.
Recovery and connective-tissue support
Support connective tissue healing and recovery during an anabolic cycle
BPC-157 and TB-500 target tissue repair and are listed as compatible additions to reduce injury risk while running LR3 for hypertrophy.
Oral GH-axis alternative comparison
Elevate IGF-1 via different pathways
MK-677 raises IGF-1 through native pituitary GH release with intact IGFBP regulation (better long-term safety, oral), whereas LR3 delivers more potent but supraphysiologic free IGF-1 that bypasses the buffer; they are considered synergistic but are more often weighed as alternatives.
Safety
Side effects & considerations
Commonly reported effects
Contraindications & cautions
- Active malignancy of any type
- Strong family history of breast, prostate, colon, or other hormonally-responsive cancers
- Diabetes mellitus and insulin resistance (elevated hypoglycemia risk)
- Hypoglycemia unawareness or history of severe hypoglycemic episodes
- Active proliferative retinopathy (IGF-1 drives retinal neovascularization)
- Pregnancy and lactation
- Pediatric or adolescent use without specialist supervision
- Concurrent exogenous insulin, sulfonylureas, or meglitinides (dangerous compounded hypoglycemia)
- Organomegaly, active intestinal disease (Crohn's, ulcerative colitis), severe cardiovascular disease, or untreated sleep apnea
Hypoglycemia from insulin-receptor cross-reactivity is the main acute risk and is preventable with 30-40g fast carbohydrate at every dose. The load-bearing long-term concern is cancer: sustained supraphysiologic IGF-1 is one of the best-characterized cancer-risk signals in clinical epidemiology (prostate, breast, colorectal), and LR3 is engineered specifically to defeat the body's IGF-1 regulatory control. Chronic high-dose use also produces acromegaly-like peripheral tissue growth. No long-term human safety data exist for IGF-1 LR3 specifically; its profile is inferred from IGF-1 axis biology and mecasermin data.
FAQ
IGF-1 LR3 — common questions
Is IGF-1 LR3 the same as native IGF-1?
No. IGF-1 LR3 adds a 13-amino-acid N-terminal extension and substitutes arginine at position 3, which reduce IGFBP binding and extend half-life from minutes to 20-30 hours. Native IGF-1 is FDA-approved as mecasermin (Increlex) for severe primary IGF-1 deficiency; IGF-1 LR3 has no approval.
How does IGF-1 LR3 differ from HGH?
HGH is an upstream signal that stimulates the liver to produce IGF-1, which then mediates most of its anabolic effects. IGF-1 LR3 bypasses that pathway and directly provides the downstream effector in a long-acting form. HGH has broader effects and, at physiologic doses, retains the IGFBP safety buffer; LR3 delivers raw, supraphysiologic free IGF1R activation regardless of pituitary function.
What is the typical IGF-1 LR3 dosage?
Beginners use 20 mcg SC once daily for 4 weeks; intermediate users 30-50 mcg for 4-6 weeks; advanced users 50-80 mcg. Always dose with 30-40g fast-digesting carbohydrate within 30 minutes, cycle 4-6 weeks on with 2-4 week washouts, never exceed 8 consecutive weeks, and never combine with exogenous insulin.
Does IGF-1 LR3 cause hypoglycemia?
Yes — it is the primary acute safety concern. LR3 cross-reacts with the insulin receptor and drives glucose uptake, so episodes can occur 30-90 minutes after injection even at 20 mcg. Prevention is dosing with fast carbohydrate, never dosing fasted, keeping glucose tabs available, and never combining with insulin.
What is 'IGF gut' or peripheral tissue growth?
Because the IGF-1 receptor is expressed on nearly every tissue, chronic high-dose LR3 grows more than muscle. Intestinal epithelial hypertrophy produces the characteristic abdominal distension ('IGF gut'), and liver, spleen, kidneys, and occasionally cardiac muscle can enlarge. These effects are generally reversible over weeks to months after stopping but illustrate that LR3 is a systemic, not muscle-specific, anabolic agent.
Does IGF-1 LR3 cause cancer?
IGF-1 LR3-specific long-term human data are absent, but sustained IGF-1 elevation is a well-documented epidemiologic risk factor for prostate, breast, and colorectal cancers, and virtually every malignancy overexpresses the IGF-1 receptor. The mechanistic concern is promotion of pre-existing occult malignant cells. Anyone with cancer risk factors should avoid it, and users should screen appropriately for age and family history.
Is IGF-1 LR3 legal and does it show on a drug test?
It is not FDA-approved for any human use and is sold under research-use-only classification; native IGF-1 (mecasermin) is the approved, distinct medical product. IGF-1 and its analogs are on the WADA Prohibited List (Section S2), and detection methods have improved, so it will show up in sport drug testing.
Why does vendor verification matter for IGF-1 LR3?
At 83 amino acids it is substantially larger than most GH-axis peptides, making synthesis quality control more variable; misfolded or truncated product can have altered activity. Independent HPLC purity, mass-spectrometry identity confirmation (expected MW ~9,111 Da), and endotoxin testing are essential.
