IGF-1 LR3

IGF-1 LR3 is full-length human IGF-1 with arginine substituted for glutamate at position 3 and a 13-residue extension added to the N-terminus. Those two changes cut affinity for IGF binding proteins by roughly a hundredfold, so a much larger fraction of the injected dose circulates free and can engage the type 1 IGF receptor. Receptor activation runs the canonical PI3K/Akt/mTOR axis, increasing protein synthesis, satellite cell proliferation and glucose uptake, and the MAPK arm drives proliferation. It also cross-reacts weakly with the insulin receptor, which is why hypoglycaemia is a real risk rather than a theoretical one. All of this is well established at the receptor level; what is not established is that any of it produces meaningful, durable hypertrophy in healthy trained humans.

Targets: IGF-1 receptor (IGF1R), PI3K/Akt/mTOR pathway, Insulin receptor (weak cross-reactivity), IGF binding proteins (evaded)

• · This is entirely anecdotal dosing. Most people who run into trouble did so by injecting on an empty stomach or stacking with insulin.
• · The claimed local-growth advantage over systemic dosing has never been demonstrated in humans; LR3's long half-life makes it a poor candidate for site-specific action anyway.
• · Doses above 50 mcg materially increase hypoglycaemia risk and are where most reported adverse events cluster. There is no evidence the extra dose buys extra muscle.

Work out your exact syringe units →

• commonHypoglycaemia— Shakiness, sweating, confusion and hunger within 20-60 minutes of injection. Keep fast carbohydrate on hand every single time you dose.
• commonInjection-site swelling or redness— Often reflects local fluid rather than muscle.
• commonHunger and lethargy— Frequently a low-blood-sugar signal rather than a separate effect.
• uncommonJaw or joint aches, carpal tunnel symptoms— The same fluid-retention pattern seen with growth hormone.
• rareOrgan and connective-tissue growth with chronic high dosing— Extrapolated from acromegaly and long-term GH/IGF excess, not from controlled LR3 data.
• rarePromotion of existing neoplasia— IGF-1R signalling is mitogenic; this is a mechanistic concern, not a documented LR3 outcome.

• Any active or suspected malignancy - IGF-1R signalling is directly mitogenic and anti-apoptotic.
• Active proliferative diabetic retinopathy.
• Concurrent insulin or sulfonylurea use without dedicated glucose monitoring - the hypoglycaemia risk compounds.
• Pregnancy and breastfeeding.
• Personal history of hormone-sensitive cancer.

• synergysomatropin — GH raises hepatic IGF-1 and IGF binding proteins; adding LR3 supplies free IGF-1 on top. Also the combination that most reliably produces hypoglycaemia and fluid retention.
• cautioninsulin-analogues — Additive hypoglycaemia. This pairing is behind most serious IGF-1 incidents reported anecdotally.
• synergymk-677 — Commonly stacked to raise the GH/IGF axis from both ends; also stacks the water retention and insulin resistance.
• redundantigf-1-des — Both hit the same receptor. Running them together mostly adds hypoglycaemia risk, not effect.

• · Fasting glucose and HbA1c before and during use.
• · Serum IGF-1 if you can get it - staying inside the age-adjusted reference range is the sane target.
• · Symptom watch for carpal tunnel, jaw ache and unusual joint swelling.
• · Age-appropriate cancer screening should be current before starting.

Not approved for human use anywhere. Sold as a research chemical, placed on the FDA's 503A Category 2 bulk substances list, and banned at all times in sport by WADA as a growth factor.

• Preclinical characterisation of Long-R3-IGF-I: reduced IGFBP affinity and increased in vivo potency in rodents (preclinical)
• Reviews of IGF-1 receptor signalling and the PI3K/Akt/mTOR hypertrophy pathway (review)
• WADA Prohibited List, section S2 (growth factors and growth hormone) (guideline)

The single most useful thing to understand about LR3 is that the binding proteins are not an obstacle it cleverly defeats - they are the delivery system it throws away. In normal physiology more than 95% of circulating IGF-1 is locked in a ternary complex with IGFBP-3 and the acid-labile subunit. That complex is a reservoir: it is too large to leave the capillary bed, so it holds IGF-1 in plasma for hours and releases it slowly at tissue. Strip that away, as the Arg3 substitution and the N-terminal extension do, and you get a molecule that is more potent per unit time at the receptor and simultaneously cleared faster from blood. Ballard's rat work showed exactly that: des(1-3)IGF-I cleared about four times faster than IGF-1 and had a nearly threefold larger steady-state volume of distribution, because nothing was holding it in the vascular compartment. Once bound, IGF1R autophosphorylates and recruits IRS-1 and Shc. The IRS-1 arm runs PI3K to PIP3 to Akt, and Akt does three separable things: it phosphorylates TSC2 to release mTORC1 and drive S6K1 and 4E-BP1 translation initiation, it phosphorylates FoxO3a and exports it from the nucleus so the MAFbx and MuRF1 ubiquitin ligases stop being transcribed, and it phosphorylates GSK-3beta, which both derepresses eIF2B and drives glycogen synthesis. That third branch, plus GLUT4 translocation from insulin-receptor cross-talk, is the entire hypoglycaemia story. The Shc arm runs Ras-Raf-MEK-ERK and is the proliferative, satellite-cell-activating and mitogenically worrying half. Clinically the effect looks the way it does - fast glucose drop, fast fluid and pump, slow and unconvincing muscle - because the Akt metabolic branch responds within minutes at doses that never sustain the translational branch long enough to matter.

Almost every serious LR3 incident traces to one of four things. Injecting fasted or before bed, so the glucose nadir arrives with no food available and, in the pre-bed case, with nobody awake to notice. Dose creep above 50 mcg on the assumption that more is more, when the literature says these variants are already 2-3 fold more hypoglycaemically potent than native IGF-1 at equal dose. Stacking with insulin. And underdosing the carbohydrate: 20 mcg with a proper meal is a non-event, 20 mcg with a protein shake is not. The second family of problems is chemical. LR3 is genuinely fragile - it wants 0.6% acetic acid rather than bacteriostatic water for anything beyond a couple of weeks, it degrades on freeze-thaw, and a shaken vial is a partly denatured vial. A great deal of 'LR3 did nothing for me' is 'the LR3 was dead on arrival'. The third family is the slow one: months of continuous use with no off-time, in someone who has never had an IGF-1 level drawn.

1. 20 mcgWeek 1 — Hold here for a full seven days with glucose monitoring before touching the dose. Inject with or immediately before a carbohydrate-containing meal, never fasted, never pre-bed.
2. 30 mcgWeek 2 — Only if week one produced no readings under 70 mg/dL and no symptomatic episodes.
3. 40 mcgWeeks 3-4 — Where most people who report anything at all are sitting. There is no evidence that going higher buys more muscle.
4. 50 mcgWeeks 5-6 — Practical ceiling. Above 50 mcg the adverse-event reports cluster hard and the benefit curve does not visibly move.

• IGF-1 receptor (IGF1R) — LR3 retains near-native or modestly reduced IGF1R affinity; the potency gain comes from IGFBP evasion, not tighter receptor binding. Francis 1992 found Long[Arg3]-IGF-I was actually less potent than IGF-1 in chicken embryo fibroblasts, a cell line secreting no detectable IGFBPs - the cleanest proof that the advantage is binding-protein escape.

  Full agonism. PI3K/Akt/mTORC1 for protein synthesis and glucose disposal, MAPK for proliferation, FoxO suppression for anti-catabolism.

• IGF binding proteins 1-6 — Roughly 100-fold reduced versus native IGF-1

  This is the engineered defect, not a target. It raises free fraction and shortens plasma residence at the same time.

• Insulin receptor — Around 100-fold lower than insulin itself for native IGF-1; not separately characterised for LR3

  Weak agonism, but at supraphysiological free concentrations it is enough to cause real hypoglycaemia rather than theoretical hypoglycaemia.

• Insulin receptor / IGF1R hybrid receptors — Not characterised for LR3

  Abundant in skeletal muscle and adipose tissue; probably contributes more to the metabolic profile than most people assume.

Glucose effects begin within 20-30 minutes and are the only thing you will reliably feel on day one. Injection-site fullness and a pump-like sensation in the trained muscle within a few days, which is fluid and glycogen, not tissue. Any genuine change in the mirror requires 4-6 weeks of consistent dosing on top of a training and eating stimulus that would have produced most of it anyway. Fluid retention, jaw ache and carpal tunnel symptoms, when they appear, show up at weeks 2-4.

The stack that actually gets people hurt is LR3 with exogenous insulin. Both hit the same glucose-lowering machinery, the effects are additive rather than redundant, and the LR3 contribution can outlast the insulin you dosed around. If you are running both, you have chosen a risk that has already killed people in this population. Stacking with growth hormone is the reverse problem and largely pointless: GH's whole anabolic mechanism is raising hepatic IGF-1, so adding LR3 is redundant on the anabolic side while stacking the fluid retention, carpal tunnel and insulin resistance. The GH-induced insulin resistance does blunt the hypoglycaemia somewhat, which is the only defensible argument for the combination. With anabolic steroids there is a real mechanistic complement - androgens act on the androgen receptor and satellite cell number, IGF1R on translation initiation - but nobody has demonstrated additivity in humans. With GLP-1 agonists it is a bad idea: you are combining an appetite suppressant that cuts carbohydrate intake with a compound whose main acute risk is hypoglycaemia.

Against DES(1-3)IGF-1: DES is more potent per microgram and much shorter-lived, so it is the one people use for a post-workout local pulse, while LR3 gives longer systemic exposure with a proportionally longer hypoglycaemia window. Against mecasermin, which is the same molecular class with actual regulatory approval and actual pharmacokinetics: mecasermin has a measured 5.8 hour terminal half-life, a known volume of distribution and a 42% hypoglycaemia rate in its trial population. LR3 has none of those numbers and no reason to be safer. Against growth hormone: GH raises IGF-1 by roughly 100-150 ng/mL through the liver with a slower, more physiological profile and a far better characterised safety record; LR3 skips the liver and skips the evidence base with it. Against the myostatin-pathway drugs in this same class, the honest comparison is embarrassing - bimagrumab has 507-subject randomised phase 2 data, and LR3 has forum posts.

$60–$180/month. Grey-market 1 mg vials typically run 40-90 USD, and 40 mcg daily consumes roughly 1.2 mg a month. The real cost is the monitoring you should be doing alongside it: a month of CGM sensors is 60-130 USD and is the single most useful thing you can buy with this compound.

• ?No human pharmacokinetic study of IGF-1 LR3 exists at all. Every half-life number circulating for it, including the widely repeated 20-30 hours, is inference or marketing rather than measurement.
• ?The animal data point the other way: binding-protein-evading IGF-1 analogues clear faster from plasma than native IGF-1, because the binding proteins are what create the long plasma residence. Whether the extended N-terminus of LR3 partly offsets this in humans is unknown.
• ?The one-letter sequence here is assembled from the published construct description ([Met1]-pGH(1-11)-Val-Asn fused to [Arg3]-IGF-I) plus the UniProt P05019 mature IGF-1 chain. It was not read directly off a database entry for LR3, because no such entry exists.
• ?Whether standard clinical IGF-1 immunoassays detect LR3 is antibody-dependent and undocumented, so an on-cycle IGF-1 result is hard to interpret.
• ?Nobody knows whether IGF-1 receptor downregulation actually occurs on the 4-6 week timescale the cycling protocols assume. The theory is plausible; the human data do not exist.
• ?The site-specific growth claim for intramuscular injection has never been tested in humans for LR3, and the long systemic exposure makes it mechanistically implausible.
• ?Published molecular weights for LongR3IGF-I cluster around 9.1-9.2 kDa but vary between suppliers, which suggests some products are not the same molecule.

• Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency Francis GL, Ross M, Ballard FJ, Milner SJ, Senn C, McNeil KA, Wallace JC, King R, Wells JR, Journal of Molecular Endocrinology, 1992 · PMID 1378742

  The paper that built Long[Arg3]-IGF-I. It defines the construct as [Met1]-porcine GH(1-11)-Val-Asn fused to [Arg3]-IGF-I, and shows the potency advantage disappears in cells secreting no binding proteins.

• Plasma clearance and tissue distribution of labelled insulin-like growth factor-I (IGF-I), IGF-II and des(1-3)IGF-I in rats Ballard FJ, Knowles SE, Walton PE, Edson K, Owens PC, Mohler MA, Ferraiolo BL, Journal of Endocrinology, 1991 · PMID 2005410

  The direct contradiction of the forum claim that binding-protein evasion lengthens half-life. Clearance 4.59 versus 1.20 ml/min/kg, volume of distribution 461 versus 167 ml/kg.

• IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in pigs and marmoset monkeys Tomas FM, Walton PE, Dunshea FR, Ballard FJ, Journal of Endocrinology, 1997 · PMID 9415072

  Ranks hypoglycaemic potency directly: IGF-I < long-IGF-I < R3IGF-I approximately LR3IGF-I < des(1-3)IGF-I, with 4- to 8-fold greater cumulative glucose suppression for the variants. The closest thing to a dose-response safety document that exists for LR3.

• Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats Tomas FM, Knowles SE, Owens PC, Chandler CS, Francis GL, Read LC, Ballard FJ, Biochemical Journal, 1992 · PMID 1371669

  One of the few studies showing a genuine anabolic effect of the LR3-class variants in vivo. Note the model: glucocorticoid-induced catabolism, not healthy trained animals.