IGF-1 LR3 Guide: Evidence & Sourcing

IGF-1 LR3 at a glance

What it is

An 83-amino-acid analogue of human IGF-1: an arginine-for-glutamate substitution at position 3 plus a 13-amino-acid N-terminal extension, both of which reduce binding to the IGF binding proteins

What it was built for

Cell culture and bioprocessing, not injection - it is manufactured and sold as a media supplement, and recombinant production methods for it are published as bioprocess papers (Appl Microbiol Biotechnol 2023, PMID 37261455)

Registered clinical trials

Zero. A ClinicalTrials.gov query for "IGF-1 LR3" and "Long R3 IGF-1" returns 0 studies (verified 2026-08-14)

Half-life

Not established in humans. The widely repeated "20-30 hours" is unsourced and points the wrong way - see the half-life section, where the FDA label and the only in vivo measurement both indicate faster clearance, not slower

Closest approved comparator

INCRELEX (mecasermin), recombinant human IGF-1, mean terminal half-life 5.8 hours after a single subcutaneous dose

Regulatory status

Not approved for human use in any jurisdiction; WADA-prohibited under S2 at all times; sold as a research chemical

Educational reference. This page does not publish dose ranges or reconstitution arithmetic.

What it is / mechanism

IGF-1 LR3 is a recombinant analogue of insulin-like growth factor-1. Native human IGF-1 is a 70-amino-acid single chain with three intramolecular disulfide bridges and a molecular weight of 7,649 Da, and its sequence is reproduced exactly in the approved product INCRELEX (mecasermin), per that product's FDA-approved labelling. LR3 differs from it in two engineered ways: glutamate at position 3 is replaced with arginine (the "R3" element), and a 13-amino-acid extension is added to the N-terminus (the "Long" element), giving an 83-amino-acid chain. Both modifications exist for one purpose, and it is the purpose that explains everything else on this page: they reduce the molecule's affinity for the IGF binding proteins. In normal physiology that binding is not an obstacle - it is the delivery system. The INCRELEX label states the arrangement directly: "In blood, IGF-1 is bound to six IGF binding proteins, with > 80% bound as a complex with IGFBP-3 and an acid-labile subunit." Circulating IGF-1 is overwhelmingly a bound molecule, and the bound fraction is protected from clearance. In a cell-culture flask, binding proteins secreted by the cells sequester added IGF-1 and blunt its effect on the culture, so an analogue that evades them is more potent per milligram and more consistent between batches. That is a genuine and well-documented advantage for bioprocessing, and it is why LR3 exists as a commercial product at all: it is a media supplement for growing cells, with published recombinant expression methods aimed at manufacturing it economically for that market (Appl Microbiol Biotechnol 2023, PMID 37261455, expressing IGF-1 and LR3 IGF-1 as xylanase fusions in Pichia pastoris). Transplanting that design rationale into a bloodstream does not carry the same implication, and the FDA label quantifies why. INCRELEX's clearance is "inversely proportional to IGF binding protein-3 (IGFBP-3) levels": apparent clearance is approximately 0.04 L/hr/kg when IGFBP-3 sits at 0.5 micrograms/mL, and approximately 0.01 L/hr/kg at 3 micrograms/mL, the median in subjects with normal IGF-1. That is a fourfold swing in clearance produced by binding-protein availability alone. A molecule engineered to escape that binding is, on the label's own logic, a molecule engineered to be cleared faster.

Researched effects

There is no human efficacy literature for IGF-1 LR3 to summarise. Nothing has been measured in a controlled human trial, because no such trial has been registered or published - the ClinicalTrials.gov registry returns zero studies for the compound under either of its common names, verified 2026-08-14. Everything circulating about what it does in people is either extrapolated from native IGF-1, extrapolated from animal and cell work, or reported anecdotally. What the preclinical literature does establish is that LR3 is biologically active in the systems it was designed for. It is used as a standard potent IGF-1 receptor agonist across cell and animal research - driving proliferation and differentiation responses in myogenic cell cultures, and producing measurable systemic effects in animals, such as the enhanced lactation performance in mice reported in J Endocrinol 2008 (PMID 18577570). A 2025 study administered long R3 IGF-1 intranasally in an Alzheimer's model and found it remodelled amyloid plaques in the cerebral cortex but failed to preserve cognitive function (J Alzheimers Dis, PMID 39610283) - a result worth stating in full because the headline finding and the outcome that mattered pointed in opposite directions. For the human context, the honest comparator is the approved recombinant IGF-1 product. INCRELEX is indicated for growth failure in pediatric patients with severe primary IGF-1 deficiency or GH gene deletion with neutralising antibodies to GH - that is, for replacing IGF-1 in people who cannot make it. It is not approved for, and its label explicitly positions it as not a substitute for, growth hormone in GH-responsive indications. There is no approved indication anywhere for administering IGF-1 or an IGF-1 analogue to a person with a normal IGF-1 axis, and no trial establishing what that does over any period. A 2026 review in Frontiers in Endocrinology (PMID 42395176) surveyed the whole class of performance-enhancing peptides marketed as "research compounds" that modulate the GH-IGF-1 axis, naming IGF-1 LR3 among them alongside PEG-MGF, the GHRH analogues and the GH secretagogues. Its summary of reported adverse effects across the class - endocrine and metabolic disturbance including dysglycaemia, fluid retention, myalgia and arthralgia, and injection-site reactions - is currently the most recent peer-reviewed characterisation of what self-administration of these compounds actually produces, and it is a description of harms rather than benefits, because the benefit side has not been studied.

Research timeline

Dated milestones taken from the primary records: the molecule's discovery, its first registered human study, the trials that shaped the evidence and the regulatory decisions. Each entry links to the record it comes from.

1. Feb 15, 1992In rats made catabolic with dexamethasone, LR3IGF-I, a variant with an N-terminal extension and arginine at position 3, is about 2.5 times as potently anabolic as IGF-I itself, even though it binds the IGF-1 receptor less well; the gain is put down to its poor binding to IGF-binding proteins. PMID 1371669
2. Jun 1992The design paper describes the Long IGF-I analogues, IGF-I fused to the first 11 amino acids of porcine growth hormone, including Long [Arg3]-IGF-I, made in E. coli; all are more potent than IGF-I in rat muscle cells. PMID 1378742
3. Dec 1997In finisher pigs, a four-day infusion of LR3IGF-I lowers daily weight gain, food intake and growth hormone, the opposite of the growth seen in rats. PMID 9488001
4. Apr 2001In food-restricted rats, a week of LR3IGF-I keeps body weight higher but does not conserve muscle protein, and in adult rats it speeds muscle protein breakdown. PMID 11472075
5. Oct 2010An anti-doping laboratory finds Long-R3-IGF-I carrying a His-tag, a purification label used for laboratory protein, in a black-market injection vial, and notes that the effects of this tagged form in humans have never been described. PMID 20675162
6. Jul 2021A French anti-doping study validates a test for LongR3-IGF-I and related analogues, which it notes were never approved for human use and are prohibited in sport; black-market products show abundant oxidized, lower-quality forms. PMID 33587816
7. Jan 2025Seven months of intranasal LR3-IGF-1 in male Alzheimer's-model mice remodels amyloid plaques in the cortex but does not preserve memory or behaviour. PMID 39610283
8. Jan 1, 2025A one-week infusion of IGF-1 LR3 into growth-restricted fetal sheep late in gestation does not improve fetal growth, although the same group had seen weight gain in normal fetal sheep. PMID 39679943

Records checked Oct 4, 2026

Claims at a glance

The claims most often made about this compound, each with the strongest kind of evidence we found for it. The grade says what was studied, not whether the claim is true; the line beside it says what that study showed.

• Builds muscle and lean massAnimal studies only. Rats given it by continuous pump infusion gained weight and retained more nitrogen; no study has given it to people. PMID 7683526
• Preserves muscle while dietingAnimal studies only. In food-restricted rats, a study built to test this found it reduced the loss of body weight but not the loss of skeletal muscle. PMID 11472075
• Creates new muscle cells (hyperplasia)No study found. The only muscle stem-cell experiment used turkey cells and a chicken version of the analogue, which was less active than chicken IGF-1; the compound itself was not tested. PMID 11469659
• Lasts long enough for once-daily useAnimal studies only. In rats it disappeared from the blood within about four hours of an intramuscular injection, while two related analogues were still detectable at 24 hours. PMID 33587816
• Improves insulin sensitivityAnimal studies only. Infused into fetal sheep, it reduced the insulin released in response to glucose; no study measured insulin sensitivity in people given it. PMID 37114757
• Protects the brain and memoryAnimal studies only. In an Alzheimer's mouse model given it in the nose for seven months, amyloid plaques changed but cognitive function was not preserved. PMID 39610283
• Speeds recovery and wound healingAnimal studies only. A rat study measured only how much of it moved from the blood into wound fluid, a very small share; no study measured healing. PMID 10607940

The reasoning behind each grade, study by study, is in this guide's Benefit & Outcome Review.

Grades checked Oct 7, 2026

Half-life & pharmacokinetics

This section retracts a figure this page previously published. Until this rebuild, this page stated a plasma half-life of "~20-30 hours (vs. ~10-16 minutes for native IGF-1)." That figure appears on a large number of vendor and community pages. Traced against the primary literature, it has no measurement behind it, and the reasoning usually attached to it runs backwards. The argument normally given is that because LR3 evades the IGF binding proteins, it stays around longer. The FDA-approved IGF-1 label says the opposite, and quantifies it. INCRELEX's clearance is "inversely proportional to IGF binding protein-3 (IGFBP-3) levels" - apparent clearance is roughly 0.04 L/hr/kg at an IGFBP-3 level of 0.5 micrograms/mL versus roughly 0.01 L/hr/kg at 3 micrograms/mL. More binding protein means slower clearance; less means faster. The label makes the same point clinically when it notes that IGFBP-3 "is greatly reduced in subjects with severe Primary IGFD, resulting in increased clearance of IGF-1 in these subjects relative to healthy subjects." Binding is what keeps IGF-1 in circulation, and LR3 was designed to bind less. The only in vivo persistence data located for LongR3 agrees with the label's logic. In the AFLD antidoping study (Drug Test Anal 2021, PMID 33587816), rats received a single 100 microgram/kg intramuscular dose of each analogue and were sampled for 36 hours. Unchanged Des(1-3)-IGF-I and R3-IGF-I were detectable until 24 hours after administration, while LongR3-IGF-I "disappeared rapidly after 4 h." Its degradation products persisted longer than the parent molecule - a new N-terminal degradation product, Des(1)-LongR3-IGF-I, was identified alongside Des(1-10)- and Des(1-11)-LongR3-IGF-I, the last detectable to 16 hours - and the same degradation pattern appeared when the analogues were incubated in human whole blood, which the authors take as grounds for extrapolating the rat observations to humans. Two caveats belong with that, and they cut against overclaiming in the other direction. A detection window in rats after intramuscular dosing is not a human subcutaneous half-life, and "disappeared after 4 h" describes the limit of an assay rather than an elimination constant. So the accurate statement is not "the half-life is 4 hours." It is that no human half-life has been measured, that the one in vivo dataset that exists shows LongR3 clearing faster than its less-modified cousins rather than slower, and that the approved label's pharmacology predicts exactly that. For scale, the measured human figure for unmodified recombinant IGF-1 is a mean terminal half-life of 5.8 hours after a single 0.12 mg/kg subcutaneous dose, with subcutaneous bioavailability estimated close to 100%. That is the only human IGF-1 half-life on this page that comes from a controlled measurement, and it belongs to a different molecule.

Storage & handling

• Lyophilised vials are typically stored refrigerated at 2-8 C and protected from light before reconstitution. The approved IGF-1 product's label specifies the same range for its unopened vials, adds "avoid freezing" and "protect from direct light," and that guidance is the closest thing to a validated storage standard for a solution of this molecule.
• The approved product's in-use limit is 30 days after first vial entry, refrigerated at 2-8 C, with unused material discarded after that. It is a preserved multiple-dose formulation, which is what makes repeated entry acceptable at all.
• That preservative is directly relevant to reconstitution choice: each mL of INCRELEX contains 10 mg of mecasermin and 9 mg of benzyl alcohol. Benzyl alcohol at 9 mg/mL is 0.9% - the same preservative at the same concentration used in Bacteriostatic Water for Injection, USP. The FDA-approved recombinant IGF-1 product is, in preservative terms, formulated the way a peptide reconstituted with bacteriostatic water is.
• Bacteriostatic water is conventionally treated as good for 28 days after first puncture when refrigerated; the approved IGF-1 product's own in-use dating is 30 days. Sterile water, which contains no preservative, does not support repeated entry into a multiple-dose vial on any timeline. Our comparison of the two is at the bacteriostatic water vs sterile water guide.
• Reconstituted peptide solutions are generally kept refrigerated, not frozen, and not shaken - diluent is directed down the vial wall and the vial swirled rather than agitated. Given that oxidised peptide forms were found in black-market products of this class before any user handling, protecting a solution from light, heat and agitation is the part of preservation actually within anyone's control.

Evidence File

The IGF-1 LR3 Evidence File: Eight Registry Queries and Five Traced Numbers

This compound has no clinical trial record, which makes the evidence question a different one: what is the nearest human evidence that exists, and where did the numbers in circulation actually come from? This module re-runs the registry under eight separate names rather than one, then reads the posted result tables of the registered trials of the unmodified parent molecule - the doses, the endpoints, the adverse-event counts and the reasons trials were stopped. It then traces the numbers that circulate about this analogue back to the papers they came from, and reports what those papers actually measured.

• 8 registry queries, 0 studies dosing a human
• 200 mcg/kg/day: the dose that stopped a registered trial
• 330 patients, 24 months, p=0.529
• 3-fold weaker at the type 1 IGF receptor

Sourcing File

The IGF-1 LR3 Sourcing File: Nine Kilodaltons, Four Ways to Get It Wrong

Most certificate guidance is generic because most of it is written without the molecule's numbers in hand. This module starts from the registered substance record - the registry identifiers, the deposited 83-residue sequence - and computes what a correct intact-mass result has to say, then works out the specific mass gaps that separate this analogue from the things most likely to be in the vial instead of it. It also does the salt-form arithmetic that sits underneath every reconstitution figure, and identifies one number in wide circulation that is a registry estimate rather than a measurement.

• 9105.3 Da: what an intact-mass result should report
• 27.06 Da separates this from its nearest analogue
• +1064.5 Da: the tag found in a real vial
• 879 mcg peptide in a 1.000 mg weighed sample

Benefit & Outcome Review

The IGF-1 LR3 Outcome Review: Twelve Claims, Three Tested Directly

Twelve claims that circulate about this compound are taken one at a time, with human, animal and cell-culture evidence kept physically separate so that no result from one tier is used to prop up a claim in another - including two effects the animal literature reports clearly and that nobody sells the compound on. Three of the twelve were tested by researchers who set out to test them, in the system the claim invokes, and those three studies are the centre of this module. It also reports what an independent peer-reviewed review concluded after a date-bounded search, and where the analogue's growth result stops travelling between species.

• 12 claims reviewed, 0 with human evidence
• 3 claims tested directly and not supported
• 0.08% of a dose per mL of wound fluid at 4 hours
• 7 months: the longest published exposure, in mice

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