IGF-1 LR3

IGF-1 LR3 (Long R3 IGF-1) is a modified form of insulin-like growth factor-1 (IGF-1), one of the body's core growth signals. It carries two engineered changes: a single amino acid swap (glutamate to arginine) and a short 13-amino-acid extension at one end of the molecule ²⁴. Together they preserve its growth-receptor signaling while nearly eliminating its binding to IGF-binding proteins (IGFBPs), the carrier molecules that normally keep most circulating IGF-1 locked up and inactive ⁴.

That design choice changes how much free, biologically active hormone is available. Native IGF-1 circulates almost entirely bound to IGFBPs, so LR3's binding-protein resistance produces a much larger unbound fraction available to activate the type-1 IGF receptor on muscle, organ, and vascular tissue ²⁰. The same receptor drive that builds tissue is also the source of the compound's main theoretical risk, potential cell overgrowth.

IGF-1 LR3 has no approved medical use in humans. The efficacy and safety evidence is almost entirely animal work (fetal sheep, pigs, guinea pigs, rats, mice) plus in vitro studies, with no human clinical trial conducted to date ¹. Despite that, it is one of the most commonly self-administered IGF-1 analogues in unregulated performance-enhancing peptide use, and blood-detection methods for it are validated in doping control ¹.

IGF-1 LR3 drives growth through one receptor while escaping the brake that normally controls it.

The receptor and the brake. LR3 binds and activates the type-1 IGF receptor (IGF-1R), a signaling protein on the surface of muscle, organ, and vascular cells, with potency comparable to native IGF-1 ³. The difference is what happens before it reaches the receptor. Native IGF-1 is mostly wrapped up by six IGF-binding proteins (IGFBPs) that buffer its activity, releasing only a small free fraction at any moment. LR3's structural changes nearly abolish IGFBP binding, so a far larger share of the dose stays free and receptor-active ²⁰. That enlarged free fraction is the basis of its long-acting anabolic signaling from infrequent dosing.

Inside the cell. Activated IGF-1R triggers a growth cascade that includes phosphorylation of the kinases ERK1 and ERK2. This step depends on proper sugar processing (N-glycosylation) of the receptor and on IQGAP1, a scaffold protein that helps assemble the signaling complex ⁸. Downstream effects documented in animal models include muscle progenitor (myoblast) proliferation and organ growth ⁹.

The feedback brake. Chronic exposure suppresses the body's own growth-hormone axis. In pigs, four days of infusion lowered growth hormone (GH), GH peak output, IGFBP-3, endogenous IGF-1, and insulin ²⁵. Calves and guinea pigs show similar axis suppression ²⁷. Repeated dosing therefore partly shuts down the very system it mimics, a counter-regulatory brake on net growth.

Glucose and the pancreas. LR3 lowers insulin. A 90-minute infusion cut glucose-stimulated insulin secretion by 66% in fetal sheep, and a one-week infusion produced a lasting beta-cell defect that persisted even in isolated islets ⁷.

Vascular and wound signals. In endothelial cells, LR3 raises HIF-1 alpha and VEGF, signals for new blood vessel growth (angiogenesis), a proposed basis for its wound-healing activity ¹⁹. It also reduced swelling and vessel-wall injury after arterial surgery in rats ¹⁵ and made atherosclerotic plaques more stable in mice ¹⁶.

What the research documents for IGF-1 LR3 is mixed, and the strongest findings are not the ones driving interest in it.

Organ growth is the most consistent effect. One-week infusions in fetal sheep increased heart, adrenal, spleen, and kidney weights ⁹. Guinea pigs gained adrenal, gut, kidney, and spleen weight ²⁸. In fetal sheep, cardiac growth was matched by proportional growth of the coronary vessels, so the enlarged heart retained normal blood supply ¹³.

Muscle hypertrophy is weakly supported. Fetal sheep showed muscle progenitor (myoblast) proliferation but no increase in hindlimb muscle mass or protein synthesis rate ¹². In a rat volumetric-muscle-loss model, LR3 delivered in a hydrogel did not improve strength, fiber size, or scarring ². In finisher pigs, a four-day infusion reduced growth rate and food intake rather than increasing them ²⁵.

Metabolic effects are consistent. LR3 suppresses glucose-stimulated insulin secretion ⁷, lowers GH, endogenous IGF-1, and IGFBP-3 ²⁵, and depletes circulating amino acids, especially branched-chain amino acids ⁴.

Tissue repair and vascular findings show promise in animals. In atherosclerotic mice, LR3 reduced narrowing and necrotic core size and produced a more stable plaque cap ¹⁶. In rats, it reduced edema and vessel-wall injury after arterial surgery, with no change in vessel patency ¹⁵. Released from a plant-stem conduit, it improved sciatic nerve regeneration in rats to a level comparable with autograft ³.

Negative studies matter too. LR3 produced no growth benefit in growth-restricted fetal sheep ⁴. Seven months of intranasal dosing remodeled amyloid plaques in Alzheimer's-model mice but did not preserve cognition ⁵.

In cancer models the effect runs both ways. LR3 limited muscle wasting in cachectic mice but accelerated tumor growth in the same animals ¹⁴.

Research protocols for IGF-1 LR3 fall into two groups: controlled laboratory infusions in animals and a community human pattern. They are not comparable in scale.

Laboratory protocols. Controlled studies used continuous intravenous infusions: 1.17 mcg/kg/hour in growth-restricted fetal sheep and 6.6 mcg/kg/hour in normal fetuses for one week ⁴; 180 mcg/kg/day for four days in pigs ²⁵; and 120 mcg/day for seven days in guinea pigs ²⁸. A local depot in a rat muscle-defect model used single doses of 28 or 280 mcg ². Per kilogram of body weight, these run far above the human community range.

Community human pattern. In unregulated human use documented in the clinical literature, protocols cluster at 20-100 mcg once daily, most commonly around 40-60 mcg, given subcutaneously or intramuscularly in 4-6-week cycles followed by a comparable off period ¹. Converted to body weight, that spans roughly 0.2-1.8 mcg/kg/day. No human dose has been validated by any clinical trial ¹.

Route. Subcutaneous injection produces measurable plasma levels in calves, while oral dosing does not ²⁷. Intranasal delivery reached brain tissue in mice but has no human dose ⁵. Continuous IV infusion generated most of the animal efficacy data and is not a self-administration route ⁴.

Timing. Insulin and glucose effects begin within 90 minutes of infusion in sheep ⁷, which is why early community practice pairs dosing with food until individual response is known. Morning dosing is favored in practitioner consensus to limit interference with overnight GH secretion, though no circadian data exist. The timeline below shows the typical community cycle structure.

IGF-1 LR3 is supplied as a lyophilized (freeze-dried) powder that must be dissolved before research use.

Diluent. Bacteriostatic water is the standard diluent, but IGF-family peptides are prone to clumping at neutral pH; recombinant LR3 concentrates in insoluble aggregates called inclusion bodies during production ³². Community practice therefore commonly uses 0.6% acetic acid as the diluent, which keeps the peptide in solution and extends refrigerated shelf life. Saline is avoided as a primary diluent.

Mixing. Community guidance is to add diluent gently and let the powder dissolve without shaking, foaming, or vigorous handling. The peptide's active shape depends on three correctly paired disulfide bonds, and misfolded intermediates accumulate under poor conditions ²⁴. Because LR3 has little binding-protein protection, minimizing surface contact during mixing also matters.

Storage. Unreconstituted vials are stored frozen at -20°C, protected from light, where they remain stable for years; refrigeration is acceptable for shorter periods. Reconstituted solution is kept refrigerated at 2-8°C. Community guidance discards bacteriostatic-water preparations after about 30 days, while acetic acid preparations may remain usable for roughly 6-12 months. Repeated freeze-thaw cycles are avoided.

Product integrity. Supply chains are unregulated, and a His-tagged Long-R3-IGF-I variant has been identified in a black-market product ¹⁷. Turbidity in a reconstituted solution is treated as a discard signal. Use the calculator below to work out dilution volumes and dose measurements.

No formal human drug-interaction studies exist for IGF-1 LR3. This section draws on animal infusion data, in vitro work, and a clinical review of GH-IGF-1-axis peptide use ¹.

Insulins and insulin secretagogues. LR3 suppresses the pancreas's own insulin release and lowers glucose ⁷, and insulin suppression replicates across pigs and sheep ²⁵. Combined with insulin or sulfonylureas, the expected result is reduced endogenous insulin with unpredictable glucose swings, so glucose monitoring is the central precaution.

Growth hormone. In pigs, LR3 lowered GH and IGFBP-3, and co-infusing growth hormone did not restore these markers or add growth ²⁵. The signals cancel rather than stack.

GHRH analogues and GH secretagogues. Secretagogues such as sermorelin, tesamorelin, CJC-1295, and the GHRPs push the pituitary to release GH, while LR3 feeds back to suppress GH output ²⁵. Combinations may blunt the secretagogue response and deepen endocrine disruption; they are common in unregulated practice but lack human evidence ¹.

Corticosteroids. Glucocorticoids are catabolic in muscle, while LR3 stimulates myoblast proliferation in animal models ¹². The mechanisms oppose; no coadministration data exist.

Anti-angiogenic agents. LR3 raises VEGF and HIF-1 alpha in endothelial cells ¹⁹, so it is mechanistically opposed to VEGF-pathway inhibitors such as bevacizumab.

Fluid-retaining drugs. Fluid retention and edema are documented class effects of GH-IGF-1-axis peptides ¹. NSAIDs, thiazolidinediones, and mineralocorticoids could add to that risk.

Supplements. Protein and amino acids are the one supportive pairing: LR3 lowers circulating amino acids, particularly BCAAs, consistent with increased tissue uptake ⁴, so adequate protein intake is standard practice. Glucose-lowering botanicals such as berberine theoretically add hypoglycemia risk. Creatine and fluid-loading supplements theoretically add to fluid retention.

Kidney disease. Chronic kidney failure alters LR3 clearance in animals ³¹, so dose behavior in renal impairment is uncertain.

Tolerance in the classic receptor-desensitization sense has not been studied for IGF-1 LR3. What accumulates with exposure is endocrine suppression, and that is what drives cycles.

Axis suppression accumulates. GH, endogenous IGF-1, IGFBP-3, and insulin all fall during LR3 treatment across species ²⁵. A week of continuous infusion in fetal sheep was enough to produce a beta-cell defect that persisted in isolated islets ¹¹. The longer the exposure, the deeper the suppression.

Recovery is presumed, not documented. No study has measured how the GH-IGF-1 axis recovers after stopping in humans. Short exposures look reversible in animals: after a 90-minute infusion, isolated islets recovered their insulin response, while a one-week infusion left a lasting defect ⁷. The standard community structure of 4-6 weeks on followed by 4-6 or more weeks off is therefore empirical, not evidence-based ¹.

Animal exposure data. Controlled studies ran 4-7-day continuous infusions in most growth work ⁴. One seven-month daily intranasal study in mice was tolerated without reported toxicity ⁵. No data define a safe maximum for intermittent human dosing.

Signals for a break. The animal and human records point to several: hypoglycemic symptoms after dosing ⁷; mid-cycle labs showing suppressed IGF-1 or IGFBP-3 ²⁵; community reports describe plateauing effects after roughly 4-5 weeks; and any unexplained new lesion, given accelerated tumor growth in a mouse cachexia model ¹⁴.

The signature finding across the peptide-peptide data is that IGF-1 LR3 works against GH-axis stacking rather than with it.

Plus GH secretagogues (GHRP-2, GHRP-6, ipamorelin, hexarelin, CJC-1295, sermorelin, tesamorelin). Secretagogues raise GH output; LR3 suppresses GH through feedback ²⁵. The combination likely blunts the secretagogue's response while compounding endocrine disruption and dysglycemia risk ¹. Stacking GH-axis peptides also makes adverse-event attribution difficult in reported human use ¹.

Plus growth hormone. In pigs, co-infusion of growth hormone with LR3 produced no additive growth and failed to restore the suppressed IGF-1, IGFBP-3, or insulin ²⁵. The animal record suggests low yield.

Plus other IGF-1 analogues (MGF, PEG-MGF, Des(1-3)-IGF-1). All act through the same IGF-1R pathway, and LR3 already suppresses endogenous IGFs ²⁸. Combinations are redundant by mechanism and add hypoglycemia and fluid-retention overlap rather than demonstrated hypertrophy ¹.

Plus ALK4/5 inhibitors (investigational). In a mouse cancer-cachexia model, LR3 combined with an ALK4/5 inhibitor spared muscle but accelerated tumor growth ¹⁴. Investigational only.

What pairing looks more grounded: because LR3 lowers circulating amino acids, especially BCAAs ⁴, protocols that pair it with adequate protein and amino acid intake align with the animal data, while GH-axis peptides oppose its feedback direction ²⁵.

United States. IGF-1 LR3 has no FDA approval for any indication. The clinical literature identifies it as an unregulated research compound sold in supply chains where composition, dose, and stacking are unverifiable ¹. It is not scheduled as a controlled substance, but products marketed with therapeutic or performance claims are unapproved new drugs under federal law. Supply integrity is a documented problem: a His-tagged Long-R3-IGF-I variant has been identified in a black-market product ¹⁷.

International. No country is documented in the peer-reviewed literature as having approved LR3 for any human indication ¹. UK and Australian frameworks treat IGF-1 as a prescription-only biologic, and LR3 has no marketing authorization in either jurisdiction. European clinical reports describe self-administration sourced from online channels rather than regulated pharmacies ¹.

Sport and anti-doping. WADA prohibits IGF-1 and its analogues at all times, in and out of competition, under category S2, and has explicitly named long-R3-IGF-I, R3-IGF-I, and Des1-3-IGF-I ¹⁰. Detection is operationally mature: blood-based LC-HRMS methods extract and quantify the intact peptide and its metabolites under WADA-compliant criteria ¹⁰. Because LR3 has no approved medical indication, a therapeutic-use exemption is effectively unavailable.

Blood sugar is the most immediate risk. LR3 is intrinsically glucose-lowering. In fetal sheep, it suppressed plasma insulin and glucose, cut glucose-stimulated insulin secretion by 66% within 90 minutes ⁷, and a one-week infusion left a beta-cell defect that persisted in isolated islets ¹¹. Dysglycemia is documented among human users of GH-IGF-1-axis peptides ¹. Community reports describe hypoglycemic symptoms (lightheadedness, sweating, shakiness, hunger) 30-90 minutes after dosing, worst when fasted.

Endocrine suppression. GH, endogenous IGF-1, IGFBP-3, and insulin fall across species ²⁵. Users describe post-cycle lethargy; recovery timing has not been studied.

Fluid retention and musculoskeletal symptoms. Class-reported effects in human use include fluid retention, arthralgia and myalgia, injection-site reactions, appetite changes, and prolactin/cortisol elevations ¹.

Amino acid depletion. Infusions lower circulating amino acids, especially branched-chain amino acids ⁴.

Cancer is the main theoretical long-term risk. LR3 accelerated tumor growth in a mouse cachexia model ¹⁴, and the IGF-1 receptor is overexpressed on many cancers ¹⁸. Human mitogenic risk is considered biologically plausible but unproven ¹; active or recent malignancy is treated as an absolute exclusion.

Higher-caution populations. Pregnancy and breastfeeding (fetal sheep data show altered insulin and glucose handling and no benefit in growth restriction ⁴); diabetes on insulin or secretagogues (additive hypoglycemia risk ⁷); chronic kidney disease (altered clearance in animals ³¹); proliferative eye disease (mechanistic extrapolation from VEGF induction ¹⁹); and children and adolescents (organ-growth effects in immature animals ⁹).

Oral dosing is ineffective. Calves given LR3 by mouth showed no detectable plasma levels, so oral products act only in the gut ²⁷.