IGF-1 LR3

IGF-1 LR3 at a Glance

IGF-1 LR3 is an engineered 83-residue IGF-1 analogue, extended and substituted so that it does not bind the IGF-binding proteins which normally hold IGF-1 inactive in circulation. It was created as a cell-culture reagent — a way to drive proliferation in serum-free laboratory media — and was never developed as a human drug at any point. It is sold as an injectable research chemical for muscle growth on the strength of that binding-protein evasion, which increases free ligand rather than improving on anything clinically established.

History & Development

Long R3 IGF-1 was never meant to go into a person. It was designed as a cell-culture reagent - a laboratory consumable for growing cells in a dish.


First described	Not established in the sources consulted for this section
Discovered / synthesised by	Not established in the sources consulted for this section
Institution	Not established in the sources consulted for this section
Origin	83-residue IGF-1 analogue - Arg substitution at position 3 plus a 13-residue N-terminal extension; IGFBP-resistant
Key patent	Not established in the sources consulted for this section
Assignee	Not established in the sources consulted for this section
Development status	Serum-free cell-culture reagent; never developed for human use, zero human trials of any kind

Discovery

Growing mammalian cells traditionally required serum, which is expensive, variable and ethically awkward. Serum-free media need defined growth factors instead, and IGF-1 is one - but ordinary IGF-1 is captured by binding proteins in culture, so much of it is wasted.

Long R3 IGF-1 solves that industrial problem. The Arg3 substitution destroys IGFBP affinity and the 13-residue N-terminal extension improves stability and expression yield, giving a potent, long-lasting, binding-protein-resistant growth factor that works reliably in a bioreactor.

Every design decision optimises it for a dish, not a body. Its potency and IGFBP resistance are manufacturing advantages; in a human they remove the regulation that keeps IGF-1 signalling in check.

Development & ownership

There is no clinical development history, because there was never a clinical intention. It has zero human trials of any kind - not efficacy, not safety, not pharmacokinetics. It has no approval and has never been submitted for one.

Its literature is what a reagent’s literature looks like: cell-culture performance data.

How it reached the market

Long R3 IGF-1 reached consumers because it was already commercially available - sold openly as a laboratory reagent, so no diversion from a pharmaceutical channel was needed. It is injected for muscle growth on the strength of IGF-1’s biology generally, by people using a research consumable whose entire design brief was to be more potent and less regulated than the natural hormone.

What It's Used For

The single most important fact about IGF-1 LR3 is what it was actually built for: it is a cell-culture reagent. Long R3 IGF-1 is an 83-amino-acid recombinant analogue of human IGF-1 (70 aa), made by adding a 13-residue N-terminal extension and substituting arginine for glutamate at position 3. Both changes cripple its binding to the IGF-binding proteins (IGFBPs) that normally sequester circulating IGF-1 — which is precisely what an industrial bioreactor wants, because a growth factor that cannot be mopped up by binding proteins in the medium stays active at low concentrations. It is sold commercially under the trademarked LONG®R3 IGF-I name as a serum-free media supplement for mammalian cell production, and that is what the overwhelming bulk of its literature is: methods work, protein engineering, recombinant expression, and its use as an IGFBP-insensitive comparator in other people’s cell experiments ^{6,15,16Reference 6Bryant KJ et al. · 1996In vitroDesign and characterisation of long-R3-insulin-like growth factor-I muteins which show resistance to pepsin digestion — in vitro (protein engineering)View study →Reference 15Pampusch MS et al. · 2005In vitroProduction of recombinant porcine IGF-binding protein-5 and its effect on proliferation of porcine embryonic myoblast cultures in the presence and absence of IGF-I and Long-R3-IGF-I — in vitro (cell culture; LR3 used as the IGFBP-insensitive comparator)View study →Reference 16Lu Z et al. · 2023In vitroRecombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris — in vitro (production methods)View study →}. It was never developed as a human therapeutic and has never entered human development. There is not one clinical trial of IGF-1 LR3, for any indication, in any registry.

Everything else is livestock and rodent physiology — guinea pig, pig, calf, rat pup, beef heifer, and a fetal-sheep growth-restriction research program — plus one mouse Alzheimer’s study, plus gray-market anabolic use that rests on IGF-1 biology, not on IGF-1 LR3 outcomes. Do not let the parent molecule’s credentials transfer. Recombinant human IGF-1 (mecasermin, marketed as Increlex) is an approved drug, with real human trials, for severe primary IGF-1 deficiency; that approval belongs to native IGF-1, not to this analogue, and it does not extend one inch. The distinction also matters against the other truncated analogue on this hub: IGF-1 DES is IGF-1 with its first three residues removed, whereas LR3 has 13 residues added plus the Arg³ swap — different molecules with different literatures, routinely conflated by vendors. Route is load-bearing: like other protein hormones it has negligible systemic oral bioavailability and is injected.

Best-supported (still animal-only):fetal and organ growth physiology. Controlled infusions into late-gestation fetal sheep reproducibly increase the weight of specific organs ^{10,12Reference 10Stremming J et al. · 2021IGF-1 [LR3] infusion to fetal sheep increases organ growth but not by stimulating nutrient transfer to the fetus — animal (fetal sheep)View study →Reference 12Jonker SS et al. · 2020Coronary vascular growth matches IGF-1 [LR3]-stimulated cardiac growth in fetal sheep — animal (fetal sheep)View study →}, and IGF-1R → PI3K/Akt/mTOR signaling is textbook biology. None of it is human, and it is one research group.

A null where it mattered most:the fetal-growth-restriction thread is the only therapeutic program that ever existed, and its 2025 read-out was negative — IGF-1 LR3 did not promote growth in growth-restricted fetal sheep, the exact population it was proposed for ^{9Reference 9White A et al. · 2025IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep — animal (fetal sheep; null result)View study →}. Along the way it also lowered fetal insulin and impaired glucose-stimulated insulin secretion through an intrinsic islet defect ^{7,8Reference 7White A et al. · 2021Reduced glucose-stimulated insulin secretion following a 1-wk IGF-1 [LR3] infusion in late gestation fetal sheep is due to an intrinsic islet defect — animal (fetal sheep)View study →Reference 8White A et al. · 2023Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets — animal (fetal sheep)View study →}. The same group then engineered a species-matched native IGF-1 specifically to get away from LR3’s unphysiological IGFBP evasion ^{11Reference 11Stremming J et al. · 2022Sheep recombinant IGF-1 promotes organ-specific growth in fetal sheep — animal (fetal sheep)View study →}.

Popular but unstudied:the muscle-building use that drives all the demand. There are no human muscle, body-composition, or performance data at all, and the whole-animal record contradicts itself across species — the analogue that grows rats reduced growth, feed intake and endogenous IGF-1 in pigs ^{2Reference 2Dunaiski V et al. · 1997Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs — animal (pig)View study →}.

The honest read:a laboratory reagent diverted into human injection. Zero human trials, contradictory animal data, a real hypoglycemia mechanism, a theoretical cancer-promotion concern, and a supply chain in which one analyzed black-market vial turned out to contain a His-tagged construct built for protein purification ^{14Reference 14Kohler M et al. · 2010Case reportDetection of His-tagged Long-R³-IGF-I in a black market product — analytical case reportView study →}.

Evidence by IndicationStrength of support · Beta

Support is an experimental score I’m building — a composite weighted by study type (human > animal > in vitro > review) and study volume. It’s a beta: a fast way to rank strength of evidence at a glance, not a validated metric. Read the low scores here carefully, because they mean two different things at once. For the muscle application the score is low because the compound has simply never been tested in a person. For the fetal-growth application it is low despite a decade of controlled animal work, because the most recent and most relevant result was a null. Each application links down to its write-up.

The only coherent, controlled research program using this molecule as a candidate therapeutic is a fetal sheep program at the University of Colorado, and it is worth reading in full because it ends badly for the compound. A one-week intravenous infusion of LR3 IGF-1 into late-gestation fetal sheep raised the weights of the heart, adrenal gland and spleen and increased skeletal-muscle myoblast proliferation — but whole fetal weight was not significantly different, and umbilical amino-acid uptake and fetal plasma amino-acid concentrations were lower, so the organ growth came from redistributing available nutrients rather than from increased placental supply ^{10Reference 10Stremming J et al. · 2021IGF-1 [LR3] infusion to fetal sheep increases organ growth but not by stimulating nutrient transfer to the fetus — animal (fetal sheep)View study →}.

Cardiac growth under LR3 was at least matched by proportional coronary vascular growth ^{12Reference 12Jonker SS et al. · 2020Coronary vascular growth matches IGF-1 [LR3]-stimulated cardiac growth in fetal sheep — animal (fetal sheep)View study →}.

Against that, the same one-week infusion lowered fetal insulin and glucose and reduced glucose-stimulated insulin secretion, and the defect persisted in islets isolated from those fetuses — an intrinsic islet lesion, not a passing systemic effect ^{7Reference 7White A et al. · 2021Reduced glucose-stimulated insulin secretion following a 1-wk IGF-1 [LR3] infusion in late gestation fetal sheep is due to an intrinsic islet defect — animal (fetal sheep)View study →}; after a shorter acute infusion the defect did not persist ex vivo ^{8Reference 8White A et al. · 2023Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets — animal (fetal sheep)View study →}.

Then the decisive result: in 2025, IGF-1 LR3 did not promote growth in late-gestation growth-restricted fetal sheep ^{9Reference 9White A et al. · 2025IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep — animal (fetal sheep; null result)View study →} — a null in the target population.

The most telling move is what the investigators did next. Noting that LR3 IGF-1’s low IGFBP affinity removes the physiological regulation of IGF-1 bioavailability, and that its sequence differs from sheep IGF-1, they built a species-matched ovine recombinant IGF-1 to test growth without that confound ^{11Reference 11Stremming J et al. · 2022Sheep recombinant IGF-1 promotes organ-specific growth in fetal sheep — animal (fetal sheep)View study →}.

That paper is not an LR3 result — it is a paper about replacing LR3, and it is cited here for exactly that reason. Older livestock work is directionally mixed. LR3 infusion increased organ growth while lowering circulating IGF-I, IGF-II and IGFBPs in guinea pigs ^{1Reference 1Conlon MA et al. · 1995Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig — animal (guinea pig)View study →}.

Dietary (luminal) long-R3-IGF-I promoted intestinal growth in artificially reared newborn rat pups ^{4Reference 4Staley MD et al. · 1998AnimalRat milk and dietary long arginine3 insulin-like growth factor I promote intestinal growth of newborn rat pups — animal (rat; dietary/luminal)View study →}.

It spared protein in feed-restricted beef heifers ^{5Reference 5Hill RA et al. · 1999Action of long(R3)-insulin-like growth factor-1 on protein metabolism in beef heifers — animal (cattle)View study →}.

Gap: No human trial, and no plan for one. The animal program is a single research group, its flagship therapeutic test returned a null, it impairs fetal insulin secretion, and the investigators themselves moved to a different molecule.

This is the reason IGF-1 LR3 is bought and the weakest-evidenced thing on the page. The rationale is genuine biology — IGF-1 is the principal mediator of growth hormone’s anabolic effects, signaling through the IGF-1 receptor and PI3K/Akt/mTOR to drive protein synthesis — and in culture, LR3 IGF-I stimulates proliferation of muscle-lineage cells, where it is typically used precisely because IGFBPs cannot buffer it ^{15Reference 15Pampusch MS et al. · 2005In vitroProduction of recombinant porcine IGF-binding protein-5 and its effect on proliferation of porcine embryonic myoblast cultures in the presence and absence of IGF-I and Long-R3-IGF-I — in vitro (cell culture; LR3 used as the IGFBP-insensitive comparator)View study →}.

But there is no human study of IGF-1 LR3 for muscle mass, body composition, strength, or performance. None. Not a trial, not a case series, not a pharmacokinetic study. The whole-animal record is worse than merely absent — it is contradictory by species: a four-day infusion in pigs decreased average daily gain and feed intake and suppressed endogenous growth hormone, IGFBP-3 and IGF-I ^{2Reference 2Dunaiski V et al. · 1997Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs — animal (pig)View study →}, the opposite of the marketed effect, while in beef heifers it spared protein under feed restriction ^{5Reference 5Hill RA et al. · 1999Action of long(R3)-insulin-like growth factor-1 on protein metabolism in beef heifers — animal (cattle)View study →}.

The bodybuilding literature consists of vendor copy and forum protocols; those are not evidence and are not scored here.

Gap: Zero human muscle, performance or body-composition data of any kind. Animal results run in opposite directions across species. The entire “anabolic” reputation is extrapolated from IGF-1 biology and from the fact that IGFBP evasion makes the molecule more potent in a dish.

Mechanisms

Target / pathway	Effect	Relevant to
IGF-1 receptor (IGF-1R)	Agonist; high receptor affinity	All applications
IGF-binding proteins (IGFBP-1 to -6)	Evades them (low BP affinity) — removes the physiological buffer on IGF-1 bioavailability	The whole design rationale; also why hypoglycemia risk is highernot lower
PI3K / Akt / mTOR	↑ protein synthesis, proliferation, cell survival	Muscleorgan growth
Insulin receptor (cross-reactivity)	Weak/partial agonism at high free-ligand concentrations	Hypoglycemia risk
Pancreatic β-cell function	↓ glucose-stimulated insulin secretion via an intrinsic islet defect (fetal sheep)	Metabolic safety
Somatotropic-axis feedback	↓ endogenous GH, IGF-I and IGFBP-3	Suppression seen across species

Pharmacokinetics

No human pharmacokinetic data exist for IGF-1 LR3 — no half-life, no bioavailability, no dose-response, no distribution study. The community figure of “~20–30 hours” has no published basis, and the “long-acting” label is a misreading of the pharmacology: what is prolonged is biological activity from unbuffered free ligand, because the molecule escapes the IGFBP/acid-labile-subunit ternary complex that normally acts as both a reservoir and a brake on native IGF-1 ^{11Reference 11Stremming J et al. · 2022Sheep recombinant IGF-1 promotes organ-specific growth in fetal sheep — animal (fetal sheep)View study →}. It is supplied as lyophilized powder and given by subcutaneous or intramuscular injection; systemic oral dosing does not work, and this has been measured directly in a relevant species — in neonatal calves, subcutaneous Long-R3-IGF-I raised plasma concentrations while an oral dose did not ^{3Reference 3Hammon H · 1997The somatotropic axis in neonatal calves can be modulated by nutrition, growth hormone, and Long-R3-IGF-I — animal (calf)View study →}. (One rat-pup study did show dietary long-R3-IGF-I promoting intestinal growth ^{4Reference 4Staley MD et al. · 1998AnimalRat milk and dietary long arginine3 insulin-like growth factor I promote intestinal growth of newborn rat pups — animal (rat; dietary/luminal)View study →}, but that is a local, luminal gut effect in a neonate, not systemic absorption, and it does not license oral use.) The analogue is intrinsically pepsin-sensitive: protein-engineering work mapped its cleavage sites and had to build mutein variants to obtain gastric stability, explicitly for possible oral applications ^{6Reference 6Bryant KJ et al. · 1996In vitroDesign and characterisation of long-R3-insulin-like growth factor-I muteins which show resistance to pepsin digestion — in vitro (protein engineering)View study →} — so the parent LR3 molecule sold on the gray market is not the stabilized one. It is produced recombinantly in expression systems such as Pichia pastoris for reagent supply ^{16Reference 16Lu Z et al. · 2023In vitroRecombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris — in vitro (production methods)View study →}. Reconstituted peptide is unstable and requires refrigeration; no independent stability data on gray-market vials were located.

Clinical & regulatory status

IGF-1 LR3 is an unapproved research chemical with no approval as a drug or dietary supplement in any jurisdiction, sold labeled “for research use only / not for human consumption.” Its only legitimate commercial identity is as a cell-culture reagent — a serum-free media supplement for biopharmaceutical production. A ClinicalTrials.gov search in July 2026 returned zero registered studies across “IGF-1 LR3”, “Long R3 IGF-1” and “LR3 IGF-I”; by contrast, the same registry holds around forty studies of mecasermin (rhIGF-1), which is a different molecule with a real approval for severe primary IGF-1 deficiency. That approval covers one indication in one population and confers nothing on the LR3 analogue. IGF-1 and its analogues are prohibited in sport at all times under the World Anti-Doping Agency’s class S2 (peptide hormones, growth factors, related substances and mimetics), and IGF-1 Long R3 is named among the GH-IGF-axis compounds encountered in unregulated self-administration in the 2026 clinical review of this class ^{17Reference 17Dominikowski A et al. · 2026ReviewThe emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration — narrative reviewView study →}.

Completed	Ongoing	Terminated	Preclinical
0(human)	0	0	~70(livestock, rodent, in vitro)

Last checked: July 2026.

Sourcing, Route & Legal Status

Regulatory status. Not approved anywhere, by anyone, as a drug or a dietary supplement — there is no marketing authorization to withdraw, because the molecule never entered human development. It is not a scheduled/controlled substance in the US, but “not scheduled” is not “approved”: marketing it for human use is unlawful in most Western jurisdictions. Prohibited in sport under WADA class S2 at all times, in and out of competition. Regulatory standing does not transfer from mecasermin (Increlex), the approved rhIGF-1 product, nor from IGF-1 DES, the other gray-market IGF-1 analogue.

How it’s supplied & administered. Vials of lyophilized (freeze-dried) powder, self-reconstituted with bacteriostatic or sterile water and injected subcutaneously or intramuscularly. Oral products cannot deliver the intact peptide systemically (see Pharmacokinetics). Reconstituted material is unstable and requires refrigeration.

Sourcing reality — and this compound has a problem the others don’t. Every gray-market peptide carries the usual risks: unverified identity, wrong or misfolded sequence, under- and over-concentration, bacterial endotoxin, non-sterile fill. IGF-1 LR3 adds a specific one on top. The material that exists in the world is made to cell-culture reagent specification, not to any standard intended for injection into a person. A reagent supplier’s obligation is that the protein reliably grows cells in a bioreactor — not that the vial is pyrogen-free, correctly folded for human dosing, or free of process-related impurities that matter in a body but not in a tank. There is no pharmaceutical-grade IGF-1 LR3 to divert, because none was ever made. The documented case is instructive: when anti-doping chemists analyzed an injection vial obtained from the black market, it contained His-tagged Long-R³-IGF-I — a construct carrying a polyhistidine purification tag, made for biochemical work, whose behavior in humans has never been studied at all; the authors judged it a by-product of laboratory research rather than a product made for injection ^{14Reference 14Kohler M et al. · 2010Case reportDetection of His-tagged Long-R³-IGF-I in a black market product — analytical case reportView study →}. Third-party certificates of analysis are a partial mitigation and can themselves be falsified. This page does not recommend, rank, or link any vendor.

Safety

No human safety data exist for IGF-1 LR3 at any dose by any route, so everything here is mechanism and animal work. The molecule is designed to escape the binding proteins that normally buffer IGF-1 — which is precisely what makes hypoglycemia its concrete acute hazard.

Safety at a Glance

Toxicity unknownDrug interactions

Hypoglycemia is the expected dose-limiting toxicity. Escaping the binding proteins delivers far more free, unregulated ligand to the insulin receptor.
Mitogenic concern grounded in mechanism. Anyone with a current or prior malignancy, or a strong family history, sits squarely inside it.
It suppresses the body’s own somatotropic axis. Across guinea pigs, pigs and cattle it lowered endogenous GH, IGF-I and IGFBP-3 rather than adding to them.
Additive with insulin and other glucose-lowering drugs. Biologically expected; never tested.
No human study of any kind exists. Not efficacy, not safety, not pharmacokinetics — the base is livestock, rodent and in vitro.
Product is reagent-grade at best. One black-market vial analyzed in the literature contained a His-tagged protein-purification construct.

Full Safety & Interactions Detail

No human safety data exist for IGF-1 LR3 — none, at any dose, by any route. Everything below is derived from IGF-1 receptor biology, the drug class, and animal studies, and is labeled as such. “No reported adverse effects” would be a statement about the absence of study, not about the compound.

Hypoglycemia is the concrete pharmacological risk, and the design of this molecule makes it worse rather than better. IGF-1 cross-reacts at the insulin receptor, and normally that activity is heavily buffered: most circulating IGF-1 is held inert in IGFBP complexes. LR3 exists specifically to escape that buffer ^{11Reference 11Stremming J et al. · 2022Sheep recombinant IGF-1 promotes organ-specific growth in fetal sheep — animal (fetal sheep)View study →}, so a given amount delivers far more free, unregulated ligand to both receptors. Insulin-like effects on glucose disposal are therefore the expected dose-limiting toxicity, and severe hypoglycemia is the plausible acute harm — particularly with the self-reconstituted, unverified concentrations described above, where the actual delivered dose is unknown. Animal infusions consistently lowered plasma glucose, insulin and amino acids ^{5,7,10Reference 5Hill RA et al. · 1999Action of long(R3)-insulin-like growth factor-1 on protein metabolism in beef heifers — animal (cattle)View study →Reference 7White A et al. · 2021Reduced glucose-stimulated insulin secretion following a 1-wk IGF-1 [LR3] infusion in late gestation fetal sheep is due to an intrinsic islet defect — animal (fetal sheep)View study →Reference 10Stremming J et al. · 2021IGF-1 [LR3] infusion to fetal sheep increases organ growth but not by stimulating nutrient transfer to the fetus — animal (fetal sheep)View study →}. Combining it with insulin, sulfonylureas or other glucose-lowering agents would be expected to be additive; this is mechanistic reasoning, not an assessed interaction.

Mitogenic / neoplasia concern. IGF-1R signaling drives cell proliferation and survival broadly, which is the reason this concern is taken seriously rather than dismissed even for regulated drugs in the class: tesamorelin, an approved medicine that raises IGF-1 only indirectly and modestly, carries a labeled contraindication in active malignancy and a requirement to monitor IGF-1 and stop if it stays elevated. IGF-1 LR3 raises IGF-1R signaling directly, with no buffer, no monitoring, and no dose control. The honest framing is a theoretical concern grounded in mechanism, not a measured incidence — but anyone with a current or prior malignancy, or a strong family history, sits squarely inside it.

Endocrine feedback suppression. Across guinea pigs, pigs and cattle, Long-R3-IGF-I lowered endogenous growth hormone, IGF-I and IGFBP-3 ^{1,2,3Reference 1Conlon MA et al. · 1995Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig — animal (guinea pig)View study →Reference 2Dunaiski V et al. · 1997Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs — animal (pig)View study →Reference 3Hammon H · 1997The somatotropic axis in neonatal calves can be modulated by nutrition, growth hormone, and Long-R3-IGF-I — animal (calf)View study →} — it suppresses the body’s own somatotropic axis rather than adding to it. In pigs this coincided with reduced growth and feed intake ^{2Reference 2Dunaiski V et al. · 1997Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs — animal (pig)View study →}.

β-cell effects. In fetal sheep, a week of infusion produced a persistent, intrinsic defect in glucose-stimulated insulin secretion that survived islet isolation ^{7Reference 7White A et al. · 2021Reduced glucose-stimulated insulin secretion following a 1-wk IGF-1 [LR3] infusion in late gestation fetal sheep is due to an intrinsic islet defect — animal (fetal sheep)View study →}. Whether anything analogous occurs with intermittent adult dosing is unstudied — but it is a signal that the metabolic effects are not limited to acute glucose lowering.

Class-level adverse effects reported for GH-IGF-axis “research peptides” in a 2026 clinical review — attributed to the class, not to IGF-1 LR3 trials, which do not exist — include endocrine and metabolic disturbance (prolactin and cortisol elevations, appetite change, dysglycemia), fluid-retention syndromes, myalgia/arthralgia, and injection-site reactions ^{17Reference 17Dominikowski A et al. · 2026ReviewThe emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration — narrative reviewView study →}.

Injection and product risks. Non-sterile technique or contaminated reagent-grade material carries infection, abscess and endotoxin risk, compounded by the sourcing problem above.

Species divergence means animal reassurance does not transfer either way. The analogue that grows organs in fetal sheep suppressed growth in pigs ^{2,10Reference 2Dunaiski V et al. · 1997Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs — animal (pig)View study →Reference 10Stremming J et al. · 2021IGF-1 [LR3] infusion to fetal sheep increases organ growth but not by stimulating nutrient transfer to the fetus — animal (fetal sheep)View study →}. Extrapolating any effect — benefit or harm — from these data to an adult human is unsound.

Who should avoid it. There is no established safe-use population, so the honest answer is everyone; the specific flags are anyone with diabetes or on any glucose-lowering drug (hypoglycemia), anyone with a current or prior cancer diagnosis or strong family history (mitogenic mechanism), anyone pregnant, breastfeeding or trying to conceive, children and adolescents, anyone subject to anti-doping testing, and anyone unwilling to inject a reagent-grade product of unverified identity and sterility.

Scope disclosure (honesty, not a claim):

Human data? None. Not one human study of any kind — efficacy, safety, or pharmacokinetic. The evidence base is livestock, rodent and in vitro.
Interactions assessed? No. Only a mechanistic caution: additive hypoglycemia with insulin and other glucose-lowering agents is biologically expected but has never been tested.
Pregnancy/lactation assessed? No. Not established; fetal-animal data are a reason for concern, not reassurance.
Long-term safety established? No. No chronic data in any species relevant to adult human use. Do not infer safety from the absence of reports.

Never imply safety from silence. Where IGF-1 LR3 has not been studied — which is everywhere a human is involved — the correct statement is “not assessed,” not “safe.”

Pregnancy & Lactation

Not established in pregnancy Not established in lactation

Not assessed / not established. There are no human pregnancy or lactation data and no reproductive-toxicity study of IGF-1 LR3. What does exist points the wrong way: the fetal-sheep literature shows this molecule alters fetal organ growth, redistributes fetal nutrient use, and impairs fetal insulin secretion ^{7,9,10Reference 7White A et al. · 2021Reduced glucose-stimulated insulin secretion following a 1-wk IGF-1 [LR3] infusion in late gestation fetal sheep is due to an intrinsic islet defect — animal (fetal sheep)View study →Reference 9White A et al. · 2025IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep — animal (fetal sheep; null result)View study →Reference 10Stremming J et al. · 2021IGF-1 [LR3] infusion to fetal sheep increases organ growth but not by stimulating nutrient transfer to the fetus — animal (fetal sheep)View study →}. Treat as contraindicated by default in pregnancy and breastfeeding.

Dosage

There is no established human dose for IGF-1 LR3, and none is recommended here. No human study has ever been conducted, so there is no dose-finding data, no bioavailability figure, no maintenance schedule, and nothing from which a dose could honestly be derived. Microgram-per-day “protocols” circulate in vendor copy and forum posts; those are not dose data, they have no experimental basis, and reproducing them here would launder marketing as evidence — so they are not given.

The doses that exist in this literature are animal infusion rates in research protocols — continuous intravenous infusions into fetal sheep, subcutaneous dosing in calves, feed-restriction studies in cattle ^{3,5,10Reference 3Hammon H · 1997The somatotropic axis in neonatal calves can be modulated by nutrition, growth hormone, and Long-R3-IGF-I — animal (calf)View study →Reference 5Hill RA et al. · 1999Action of long(R3)-insulin-like growth factor-1 on protein metabolism in beef heifers — animal (cattle)View study →Reference 10Stremming J et al. · 2021IGF-1 [LR3] infusion to fetal sheep increases organ growth but not by stimulating nutrient transfer to the fetus — animal (fetal sheep)View study →} — expressed per kilogram in species with different IGF-1 physiology, delivered by routes and schedules nobody self-administering uses. They are not translatable and are not reproduced as guidance. Two further points bear on dose specifically: because LR3 evades IGFBPs, the free-ligand exposure from a given nominal dose is much higher than the same number of micrograms of native IGF-1 would suggest, and because gray-market vials are self-reconstituted reagent-grade material of unverified content, the delivered dose is unknown even to the person injecting it. This entry is informational only and is not an endorsement of use.

References

Conlon MA, Tomas FM, Owens PC, et al. (1995). Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig — animal (guinea pig). Journal of Endocrinology. https://pubmed.ncbi.nlm.nih.gov/7561636/
Dunaiski V, Dunshea FR, Walton PE, et al. (1997). Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs — animal (pig). Journal of Endocrinology. https://pubmed.ncbi.nlm.nih.gov/9488001/
Hammon H, Blum JW (1997). The somatotropic axis in neonatal calves can be modulated by nutrition, growth hormone, and Long-R3-IGF-I — animal (calf). American Journal of Physiology. https://pubmed.ncbi.nlm.nih.gov/9252489/
Staley MD, Gibson CA, Herbein JF, et al. (1998). Rat milk and dietary long arginine3 insulin-like growth factor I promote intestinal growth of newborn rat pups — animal (rat; dietary/luminal). Pediatric Research. https://pubmed.ncbi.nlm.nih.gov/9773839/
Hill RA, Hunter RA, Lindsay DB, et al. (1999). Action of long(R3)-insulin-like growth factor-1 on protein metabolism in beef heifers — animal (cattle). Domestic Animal Endocrinology. https://pubmed.ncbi.nlm.nih.gov/10370861/
Bryant KJ, Read LC, Forsberg G, et al. (1996). Design and characterisation of long-R3-insulin-like growth factor-I muteins which show resistance to pepsin digestion — in vitro (protein engineering). Growth Factors. https://pubmed.ncbi.nlm.nih.gov/8919033/
White A, Stremming J, Boehmer BH, et al. (2021). Reduced glucose-stimulated insulin secretion following a 1-wk IGF-1 [LR3] infusion in late gestation fetal sheep is due to an intrinsic islet defect — animal (fetal sheep). American Journal of Physiology — Endocrinology and Metabolism. https://pubmed.ncbi.nlm.nih.gov/33938236/
White A, Stremming J, Brown LD, et al. (2023). Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets — animal (fetal sheep). Journal of Developmental Origins of Health and Disease. https://pubmed.ncbi.nlm.nih.gov/37114757/
White A, Stremming J, Wesolowski SR, et al. (2025). IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep — animal (fetal sheep; null result). American Journal of Physiology — Endocrinology and Metabolism. https://pubmed.ncbi.nlm.nih.gov/39679943/
Stremming J, Heard S, White A, et al. (2021). IGF-1 [LR3] infusion to fetal sheep increases organ growth but not by stimulating nutrient transfer to the fetus — animal (fetal sheep). American Journal of Physiology — Endocrinology and Metabolism. https://pubmed.ncbi.nlm.nih.gov/33427051/
Stremming J, White A, Donthi A, et al. (2022). Sheep recombinant IGF-1 promotes organ-specific growth in fetal sheep — animal (fetal sheep). This study tested a species-matched ovine IGF-1, not LR3; it is cited here because the authors state their reason for building it — LR3 IGF-1’s low IGFBP affinity removes the physiological regulation of IGF-1 bioavailability. Frontiers in Physiology. https://pubmed.ncbi.nlm.nih.gov/36091374/
Jonker SS, Giraud GD, Chang EI, et al. (2020). Coronary vascular growth matches IGF-1 [LR3]-stimulated cardiac growth in fetal sheep — animal (fetal sheep). The FASEB Journal. https://pubmed.ncbi.nlm.nih.gov/32573852/
Engel MG, Narayan S, Cui MH, et al. (2025). Intranasal long R3 insulin-like growth factor-1 treatment promotes amyloid plaque remodeling in cerebral cortex but fails to preserve cognitive function in male 5XFAD mice — animal (mouse; cognitive null). Journal of Alzheimer’s Disease. https://pubmed.ncbi.nlm.nih.gov/39610283/
Kohler M, Thomas A, Walpurgis K, et al. (2010). Detection of His-tagged Long-R³-IGF-I in a black market product — analytical case report. Growth Hormone & IGF Research. https://pubmed.ncbi.nlm.nih.gov/20675162/
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Lu Z, Liu N, Huang H, et al. (2023). Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris — in vitro (production methods). Applied Microbiology and Biotechnology. https://pubmed.ncbi.nlm.nih.gov/37261455/
Dominikowski A, Rękoś Z, Olejarz M, et al. (2026). The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration — narrative review. Frontiers in Endocrinology. https://pubmed.ncbi.nlm.nih.gov/42395176/