Research information only. PrecisePep is an educational library. It is not medical advice and is not intended to assist, encourage or enable self-administration. The compounds documented here are research chemicals — most are not approved for human use. Read the full disclaimer.
PrecisePep/Peptide Library/IGF-1 LR3
Growth Hormone & Anabolic Support
Long R3 IGF-1 · LR3 · insulin-like growth factor 1 analogue
An engineered IGF-1 analogue designed to escape the binding proteins that normally regulate it — which is precisely why it is potent, and precisely why it is the most consequential compound in this library.
IGF-1 LR3 was designed as a laboratory reagent, not a drug. Native IGF-1 circulates almost entirely bound to IGF binding proteins, which control its availability moment to moment. LR3 carries an arginine substitution at position 3 and a 13-residue N-terminal extension, and the point of both modifications is to reduce IGFBP binding so the molecule stays free and active. In cell culture, that makes it a more reliable and potent growth stimulus — which is what it was made for.
Administered to a person, the same property removes a physiological control system. Native IGF-1 activity is buffered by binding proteins; LR3 activity substantially is not, and its half-life is roughly twenty to thirty hours rather than ten minutes.
Two consequences follow directly. IGF-1 has meaningful insulin-receptor cross-reactivity, so unbuffered activity carries genuine hypoglycaemia risk. And IGF-1 is a growth factor — signalling proliferation and inhibiting apoptosis is what it does, everywhere, without discriminating between tissue you want to grow and tissue you do not.[2]
Two distinct hazards, both real: acute hypoglycaemia, which can be severe and rapid, and chronic mitogenic signalling, where elevated IGF-1 is one of the better-established epidemiological associations with cancer risk. Neither is speculative in the way most concerns on this site are.
IGF-1 receptor agonism. Activates the IGF-1R tyrosine kinase, driving PI3K/Akt and MAPK signalling — the canonical growth, proliferation and anti-apoptotic pathways. Downstream this means protein synthesis, satellite cell activation and hyperplastic as well as hypertrophic muscle signalling.
Binding-protein evasion. The Arg³ substitution and N-terminal extension reduce affinity for IGFBPs. In culture this prevents the reagent being sequestered; in a person it removes the buffering that normally makes IGF-1 activity local and transient.
Insulin receptor cross-reactivity. IGF-1 and insulin receptors are structurally related, and IGF-1 has appreciable affinity for the insulin receptor. Unbuffered, long-acting IGF-1 activity therefore lowers blood glucose — the mechanism behind the acute risk.
Anti-apoptotic signalling. Akt activation suppresses apoptosis. This is the same property that makes IGF-1 a growth factor and the reason its elevation is scrutinised in oncology.
Effects that have been reported. A study-tier entry means a result was published — not that the effect is established, reproducible, or transferable from a rodent to a person.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
LR3 is widely used in bioprocessing and cell culture precisely because binding-protein evasion makes it a more consistent and potent stimulus than native IGF-1. This is its actual validated use.
Well established endocrinology — GH acts largely through hepatic IGF-1, and IGF-1 drives muscle protein synthesis and satellite cell activation.
Higher circulating IGF-1 is associated with increased risk of several cancers in large observational studies. Association rather than proof of causation from exogenous administration — and among the more robust signals of its kind.
Mecasermin (recombinant human IGF-1) is approved for severe primary IGF-1 deficiency, with a label carrying a prominent hypoglycaemia warning and requiring food intake around dosing.
The analogue has never been evaluated in humans for any indication.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
The reason it is used. Satellite cell activation and hyperplastic signalling are real IGF-1 properties in models; translation to meaningful human muscle gain from exogenous LR3 has never been tested.
A persistent community belief. LR3 is specifically engineered to evade the binding proteins that make IGF-1 act locally — so site-specific action is the property this molecule most conspicuously lacks.
Follows from growth factor signalling. Unstudied.
From the insulin-receptor cross-reactivity. The same mechanism as the hypoglycaemia risk.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
The characteristic report, plausibly reflecting glycogen and fluid shifts from insulin-receptor activity rather than tissue growth.
Shakiness, sweating, confusion and intense hunger are commonly reported — a genuine and predictable pharmacological effect, not a nuisance side effect.
Community practice universally pairs dosing with food. That instinct is correct and mirrors the mecasermin label.
Frequently reported and attributed to IGF-1 receptor expression in intestinal tissue.
Even in a community not known for caution, LR3 is commonly described as one to approach carefully. That consensus is worth noting.
Adverse effects, contraindications and unknowns. The grey-market tier is where under-reporting is worst: uncontrolled use produces no systematic safety surveillance at all, so absence of a reported harm is not evidence of safety.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
The dominant acute risk. The approved IGF-1 product carries a prominent hypoglycaemia warning and requires food intake shortly before or after dosing — and that product is native, binding-protein-buffered IGF-1.
Elevated IGF-1 is associated with increased risk of several cancers in large cohort studies, and IGF-1R signalling is an active oncology drug target — in the inhibition direction.
Include hypoglycaemia, tonsillar hypertrophy, injection-site lipohypertrophy and intracranial hypertension.
The compound with reduced binding-protein buffering and a much longer half-life is the one with no human characterisation at all.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
A twenty-to-thirty-hour half-life means the hypoglycaemia risk window is not a couple of hours. Eating once at injection does not cover it.
Stacking anything glucose-lowering with an unbuffered IGF-1 analogue is the most dangerous combination documented anywhere on this site.
Anti-apoptotic, pro-proliferative signalling systemically, without buffering, over months.
IGF-1 receptors are widely expressed. Growth signalling does not confine itself to skeletal muscle.
Secretagogues raise endogenous IGF-1; adding an exogenous unbuffered analogue stacks the same signal from two directions.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
Commonly reported, occasionally severe. This is the effect to plan around.
Near-universal, and a direct consequence of the glucose effect.
Frequently reported.
Reported, plausibly glycaemic.
Figures below are documented, not recommended. Study ranges come from published protocols in the stated model; grey-market ranges are what the research community reports using and carry no safety validation of any kind.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
Titrated by body weight with mandatory food intake around each dose, in a narrowly defined deficiency population. Note this is native IGF-1, not LR3.
Every figure in circulation is community-derived for a molecule engineered as a culture reagent.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Mirrors the approved product requirement, and the long half-life means one meal is not sufficient coverage.
A glucose meter is inexpensive and directly measures the acute risk. This is the clearest case in the library for measuring rather than guessing.
Both risks scale with cumulative exposure.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
The common community range, typically post-training with food.
Higher range, with correspondingly more reported hypoglycaemia.
Shorter courses than most compounds here, reflecting the risk profile.
| Approach | Dose | Frequency | Timing |
|---|---|---|---|
| Conservative | 20 mcg | Daily | With carbohydrate |
| Standard | 40 – 50 mcg | Daily | Post-training, with food |
| Higher-end | 80 – 100 mcg | Daily | More hypoglycaemia reported |
Combination effects. Almost no peptide combination has been studied as a combination in humans; stack logic is overwhelmingly mechanistic inference and community practice. Each linked compound has its own page.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
None.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
The bone-density argument for IGF-1 runs through turnover markers. Teriparatide runs through randomised fracture data — it is a 34-residue parathyroid hormone fragment, approved since 2002, and it is the anabolic bone peptide that actually exists. It also carries the opposite risk profile: its rat osteosarcoma signal was investigated in large human cohorts and not reproduced, which is more than can be said for the proliferative concerns around an unregulated IGF-1 analogue.
Insulin, sulfonylureas, incretin agonists. This combination is the most acutely dangerous documented on this site.
Secretagogues raise endogenous IGF-1; LR3 adds unbuffered exogenous IGF-1. The mitogenic exposure adds.
Stacking with pro-angiogenic repair peptides and a telomerase inducer combines several independent proliferative pressures in one protocol.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
Common in performance stacks, and the combination that maximises total IGF-1 exposure.
Whole schedules — dosing, titration, cycle length, and off-time — as documented in trials, as proposed from mechanism, and as circulated in the research community. Reproduced for study and comparison only.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
Weight-based twice-daily dosing with mandatory food, in severe primary IGF-1 deficiency, with glucose monitoring.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
The three things that directly address the acute risk.
The mitogenic association is one of the better-established in this whole library.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
The general community pattern.
Neither the Gold Standard Protocol nor the 15-Compound Matrix includes it.
IGF-1 LR3 is the compound in this library with the widest gap between how casually it is used and how seriously its two principal risks are taken. Both risks are direct consequences of the molecule working as designed, and both have an approved-drug precedent that shows what handling them properly looks like.
An approved recombinant IGF-1 exists. Mecasermin is licensed for severe primary IGF-1 deficiency, and it is dosed with food, titrated against blood glucose, and carries hypoglycaemia as its defining hazard. IGF-1 LR3 is a modified analogue designed to evade the binding proteins that normally restrain IGF-1 in circulation — which extends its half-life and removes the brake at the same time. It is not approved anywhere, for anything.
Pathophysiology
IGF-1 has structural homology with insulin and cross-reacts with the insulin receptor. At sufficient concentration it lowers blood glucose directly, and it does so without the counter-regulatory signalling that normally limits an insulin excursion.
Mechanistic rationale
The binding proteins IGF-1 LR3 was designed to escape are the system that keeps free IGF-1 low. Removing that restraint is the entire point of the modification and it is also the mechanism of the hypoglycaemia risk. Mecasermin, the approved IGF-1, is given with a meal for exactly this reason and its label is built around glucose monitoring. Nobody using LR3 is doing either.
Community reports
Shakiness, sweating, confusion and hunger after dosing are described in community spaces and usually attributed to "the peptide kicking in". Those are hypoglycaemia symptoms. A glucose meter costs very little and is the single most useful piece of equipment anyone using this compound could own.
Components carrying the argument: Insulin receptor cross-reactivity — unbuffered
Pathophysiology
IGF-1 receptor signalling drives proliferation and suppresses apoptosis. It is one of the most studied growth-signalling axes in oncology, and IGF-1R inhibitors were developed as anticancer agents precisely because of it.
Mechanistic rationale
Epidemiological work associates higher circulating IGF-1 with the incidence of several common cancers. The counterpoint that usually gets raised — Laron syndrome, where IGF-1 deficiency is associated with near-absence of cancer — actually reinforces the direction rather than undermining it. This compound raises free, unbuffered IGF-1 systemically and is designed to keep it there. No human study has shown it causes cancer, because none has looked.
Community reports
Raised occasionally in community discussion and generally dismissed. It is the one place in this library where the mechanistic concern and the compound’s stated purpose are the same thing described twice.
Components carrying the argument: Free IGF-1, systemic and sustained
Pathophysiology
IGF-1 signalling activates the PI3K/Akt/mTOR pathway, drives satellite cell activation and protein synthesis, and is a genuine mediator of hypertrophy.
Mechanistic rationale
The mechanism is real. What is missing is any controlled human evidence that exogenous IGF-1 analogue produces functional benefit, and the pattern across this whole axis — clearest in the ROMANA cachexia trials, where lean mass rose and handgrip strength did not — is that mass and function separate. Local hypertrophy at injection sites is also frequently described, which is a cosmetic outcome rather than a strength one.
Community reports
Site-specific fullness is the most commonly reported effect and is consistent with local action. Systemic strength claims are much less consistent.
Components carrying the argument: PI3K/Akt/mTOR, satellite cell activation
Pathophysiology
IGF-1 is involved in collagen synthesis and fibroblast proliferation, so a repair rationale exists on paper.
Mechanistic rationale
The problem is the exchange rate. For soft-tissue repair there are compounds with the same tier of evidence — rodent data — and none of the hypoglycaemia or growth-signalling liability. Choosing the compound with the worst risk profile for an application where cheaper alternatives share the same weak evidence is a poor trade, and it is worth naming as such.
Community reports
Used in injury protocols, usually alongside BPC-157 and TB-500, which makes attribution impossible.
Components carrying the argument: Collagen synthesis, fibroblast proliferation
Pathophysiology
IGF-1 is genuinely involved in bone formation and is one of the mediators through which GH acts on the skeleton.
Mechanistic rationale
Turnover markers are not fracture reduction. Teriparatide has randomised fracture data, has been approved since 2002, and had its own rat carcinogenicity signal investigated in large human cohorts and not reproduced — which is more scrutiny than anything on this page has received.
Community reports
Rarely the stated reason for use; appears as supporting argument in longevity framing.
Components carrying the argument: IGF-1 in bone formation
Pathophysiology
The tissue changes of acromegaly — soft tissue thickening, arthropathy, cardiomyopathy, visceromegaly — are largely IGF-1 mediated. IGF-1 is the effector, GH is the signal.
Mechanistic rationale
A secretagogue raises IGF-1 through the pituitary, which retains feedback. This compound delivers the effector directly and bypasses every feedback mechanism that limits it. That is a meaningful difference in kind, not just in degree, and it is the reason this compound sits at the far end of this cluster.
Community reports
Fluid retention, joint aching and jaw or hand changes are reported at higher doses and longer durations.
Components carrying the argument: Downstream effector, no feedback
| Question | Position |
|---|---|
| Approved anywhere? | No. Mecasermin is the approved IGF-1 — a different molecule |
| Why "LR3"? | Modified to evade IGF binding proteins — longer half-life, no brake |
| Most immediate risk | Hypoglycaemia — insulin receptor cross-reactivity |
| What the approved drug does about it | Dosed with food, titrated against blood glucose |
| Oncological concern | IGF-1R drives proliferation — an anticancer drug target |
| Muscle | Mechanism real; function unproven; mass separates from strength |
| Bone | Teriparatide has fracture data; this has markers |
| Versus a secretagogue | Bypasses pituitary feedback entirely |
For muscle and function: progressive resistance training with adequate protein — roughly 1.2–1.6 g/kg/day in older adults, distributed across meals — has the best evidence of any intervention, and improves function rather than only mass. Nothing on this page substitutes for it, and the ROMANA result is the reason to say so.
For tendinopathy: progressive mechanical loading over months outperforms every injectable it has been compared against.
For bone: teriparatide or abaloparatide for anabolic effect, bisphosphonates or denosumab to consolidate, vitamin D and calcium, progressive loading.
For severe primary IGF-1 deficiency — the condition an IGF-1 drug actually treats — mecasermin (Increlex) is the approved therapy, licensed from two years of age and given under endocrinology supervision with meals and glucose monitoring. It changed hands in December 2024 and is distributed in the United States through a single specialty pharmacy, which is what access to a genuine IGF-1 product looks like: a rare-disease pathway with a prescriber, not a vial.
Physical-chemistry reference for laboratory handling of the lyophilised material. Reproduced so that stability and concentration mathematics can be studied — see the calculator for the arithmetic and the reconstitution guide for sterile technique.
Supplied lyophilised, commonly 1 mg per vial. LR3 is often supplied with acetic acid or a low-pH diluent rather than plain bacteriostatic water, because solubility and stability differ — follow the supplier specification rather than assuming.
Lyophilised: −20 °C. Reconstituted: 2–8 °C, and stability is shorter than for simple peptides.
Commonly 1 mg lyophilised vials.
A 83-residue protein rather than a short peptide, and correspondingly more fragile. Agitation, temperature cycling and inappropriate diluent all degrade it.
Regulatory status changes and differs by country. This is a summary for orientation, not legal advice — check your own jurisdiction.
Not approved for human use. IGF-1 LR3 is sold as a laboratory reagent for cell culture and bioprocessing — that is its legitimate market, and the labelling reflects it.
Mecasermin (native recombinant IGF-1) is approved for severe primary IGF-1 deficiency with a hypoglycaemia warning and defined monitoring. That approval does not extend to an engineered analogue designed to evade the regulatory system that makes native IGF-1 manageable.
Regulatory and trial claims re-checked against primary sources on 16 August 2026. Checked: mecasermin (Increlex) approval, ownership and distribution status. Approvals, trial readouts and compounding decisions move faster than anything else on this page — a date here means someone looked, not that nothing has changed since.
IGF-1 and its analogues are explicitly named on the WADA Prohibited List under S2 (growth factors). Prohibited at all times.
Links resolve to PubMed records, trial registries, publisher pages or primary documents. Where a body of work rather than a single paper is cited, the link opens a PubMed query so the full result set — including newer papers than this page — can be reviewed. Verify every claim against the primary source before relying on it.
For educational and research reference only. Nothing on this site is medical advice, a recommendation, or an instruction to administer any substance to a human being. Every figure on this page is a record of what has been reported, not a recommendation. Full disclaimer.
