Peptide Health Lab

Growth hormone axis

IGF-1 LR3

FOR RESEARCH PURPOSES ONLY

Also known as: Long R3 IGF-1, LR3 IGF-1, Long-R3-IGF-I

Regulatory status
Research only
Evidence grade
Animal studies only

Last reviewed September 1, 2026 · 13 sources

What IGF-1 LR3 is and how it works

IGF-1 LR3 is a laboratory-engineered variant of insulin-like growth factor-1. Two changes separate it from the native hormone: the glutamate at position 3 is replaced by arginine, and a 13-amino-acid extension derived from methionyl porcine growth hormone is attached to the N-terminus. Both changes exist for one reason, and it is not potency at the receptor. They are there to stop the molecule binding to the IGF-binding proteins.

In circulation, native IGF-1 is almost entirely bound. It travels in a 140-kilodalton ternary complex with IGF-binding protein 3 and an acid-labile subunit, which is what gives the hormone its long half-life and what keeps its free concentration under tight control.[8] The binding proteins are the brake. An analog that evades them is not simply "more IGF-1"; it is IGF-1 with the regulatory layer removed, which is a different pharmacological object even though the receptor it activates is the same one.

That design goal is measurable in cell culture. When recombinant IGFBP-3 was added to L6 myogenic cell cultures, it inhibited native IGF-I-stimulated proliferation and differentiation, while long-R3-IGF-I was comparatively resistant to the same inhibition.[4] Purified LR3 IGF-1 produced by recombinant expression shows cell-proliferation bioactivity comparable to an IGF-1 standard, which is how the analog is characterized when it is made: as a reagent whose bioactivity is confirmed in a proliferation assay.[5]

That is the honest frame for this compound. IGF-1 LR3 was developed and is overwhelmingly used as a research reagent — a cell-culture supplement and an animal-model tool — and it has been characterized as a reagent rather than as a drug. It has never been approved for use in humans anywhere, and no development programme has taken it toward approval.[1]

One clarification decides how everything below should be read. Mecasermin — recombinant human IGF-1 — is a different molecule with its own FDA approval. It is native IGF-1, not the analog, and it is approved for severe primary IGF-1 deficiency and for growth hormone gene deletion with neutralizing antibodies to growth hormone.[8] Its trials, its label, and its outcome registry describe that molecule in that population.[9] Nothing about that approval transfers to IGF-1 LR3, and no evidence generated with mecasermin is evidence about the analog. The two are related the way a drug and a modified version of it are related, which is to say: enough to explain the mechanism, not enough to share a conclusion.

What the research actually shows

No human study exists. That sentence is the whole of the human evidence section, and it is stated first because everything else on this page is animal or in vitro work that gets misread the moment it is read out of order. No published randomized trial, controlled study, open-label series, or case report has administered IGF-1 LR3 to a person and measured muscle mass, strength, body composition, recovery from injury, or anything else. A 2026 review of performance-enhancing peptides acting on the growth-hormone/IGF-1 axis describes this gap directly — self-administration of these compounds has run far ahead of any clinical evidence base.[10]

The animal evidence reports selective tissue growth, not whole-body anabolism. Female guinea pigs infused continuously for seven days with long R3 IGF-I showed increased fractional weights of adrenals, gut, kidneys and spleen — and no significant change in body weight gain, feed intake, feed conversion efficiency, or carcass composition. Plasma IGF-I, IGF-II and binding-protein concentrations fell.[2] In rats infused for seven days, the analog increased jejunal glucose uptake by up to 69% per centimetre of intestine, an effect the authors attributed to increased mucosal mass rather than to upregulated epithelial glucose transporters; native IGF-I did not produce the same effect.[6] In neonatal calves, subcutaneous long R3 IGF-I raised its own plasma concentration, lowered native IGF-I, decreased circulating growth hormone, and increased IGFBP-2, demonstrating that the somatotropic axis responds to the analog.[7]

The consistent thread across those studies is that the tissues that grew were viscera — gut, kidney, spleen, adrenals — not skeletal muscle, and that overall growth was not stimulated in the animals where it was measured. That is a notable mismatch with the reason the compound has a reputation.

The one long-duration animal study reports a negative primary result. Male 5XFAD mice were given intranasal long R3 IGF-1 for seven months. Body composition improved and some measures of amyloid plaque morphology in the cerebral cortex shifted favorably, but across multiple assays the treatment did not significantly alter cognitive symptoms, and the authors concluded the data do not support the analog as a monotherapy.[3] Seven months of exposure in a transgenic disease model is the longest published administration of this molecule in any species, and its headline endpoint failed.

The clearest human-relevant data is analytical, not clinical. An anti-doping laboratory validated a mass-spectrometry method for long R3 IGF-I and related analogs and evaluated their detectability after intramuscular administration in rats. Unchanged long R3 IGF-I disappeared rapidly, within about four hours, while N-terminal degradation products including Des(1)-LongR3-IGF-I were detectable considerably longer. The same degradation products appeared after in vitro incubation in human whole blood, which the authors took as reason to expect the rat observations to extrapolate. The study also reports abundant signs of lower-quality, oxidized peptide forms in the circulating preparations it examined.[1]

Where the evidence is weak

There is no human evidence at all, and that is a different situation from weak human evidence. Most compounds on this site have some human data that is small, uncontrolled, or badly designed. This one has none. There is no trial, no registry, no case series, no dose-finding study, and no adverse-event record. Every claim made for IGF-1 LR3 in the context of training or recovery is an extrapolation from cell culture and rodents, made across a species gap, a dose gap, an endpoint gap, and a population gap simultaneously.

The animal findings do not point where the compound's reputation points. Where hypertrophy has been the endpoint, it has generally not been the finding. Guinea pigs grew viscera and not carcass.[2] Rats grew intestinal mucosa.[6] Calves showed an endocrine response with suppression of their own axis.[7] Mice given the longest exposure on record improved body composition but failed the cognitive endpoint the study was built around.[3] None of that adds up to a demonstrated muscle-building effect in any species.

Evidence about the parent molecule is routinely misattributed to the analog, and that is the single most common error made about this compound. Mecasermin has an approval, a label, trials, and an outcome registry in a defined pediatric deficiency population.[8][9] The analog has none of those things. The modifications that define IGF-1 LR3 were introduced specifically to change how the molecule behaves in circulation, so pharmacology established for the native hormone is the least transferable part of the picture, not the most.

The pharmacokinetics that are published are short and awkward. Unchanged analog cleared from rat plasma within about four hours after intramuscular administration, with degradation products outlasting the parent compound.[1] Nobody has characterized what those degradation products do biologically. A molecule whose measurable presence is brief and whose fragments persist is not a well-understood exposure.

Identity and purity are unresolved for anything carrying this name. With no approved manufacturer there is no assay standard, no release specification, and no lot testing, and the published analytical work found real, documented degradation in the preparations it examined.[1] Nothing guarantees that material labeled with this name is this molecule, at the stated concentration, in undegraded form.

Nothing is known about long-term exposure in humans. The nearest relevant signal is epidemiological and it is not about this compound: higher circulating IGF-1 is associated with the risk of several cancers in large prospective cohorts, most consistently prostate cancer.[12][13] That describes naturally varying IGF-1 in people taking nothing and cannot be read as a measured risk of the analog. It is the reason the malignancy question belongs in a clinical conversation rather than a training forum.

Legal and regulatory status

IGF-1 LR3 is not approved by the FDA for any indication, and it has never been approved for human use by any regulator. A search of approved drug products returns no application for this analog; the only approved product in the IGF-1 family is mecasermin, which is native recombinant human IGF-1 and a different molecule.[8] The analog is distributed for laboratory research use, which is why every mention of it on this site carries research-only framing. Anti-doping researchers state the position plainly: IGF-1 analogs of this class were never approved for use in humans yet remain readily available for bodybuilding use.[1]

In tested sport the status is unambiguous. IGF-1 and its analogs, with long R3 IGF-I named among them, are prohibited substances, and validated immunopurification and high-resolution mass-spectrometry methods now detect the analog and its N-terminal degradation products at antidoping-relevant sensitivity.[1] Detection is no longer theoretical, and a 2026 review places these compounds squarely in the category where self-administration has outrun both the evidence and the regulation.[10]

What the regulatory status means for a reader is narrower and more useful than any argument about enforcement: there is no label, no approved manufacturer, no assigned indication, and no regulated quality standard behind anything carrying this name. PHL does not sell peptides and takes no position on how unapproved material reaches anyone.

Questions to bring to a provider

The useful conversation is not "how would I run IGF-1 LR3." Given that no person has ever been given this molecule in a published study, the honest question is prior to that: what problem is actually being solved, and is the IGF-1 axis involved in it at all? Questions worth raising:

  • Is there any reason to think the growth-hormone/IGF-1 axis is abnormal here, and what testing would establish that rather than assume it?[8]
  • Given that no human has been administered this analog in any published study, what would count as evidence that it did anything at all — and what would count as evidence that it was safe?[10]
  • If the underlying question is genuinely about IGF-1 deficiency, is there an approved product and a defined indication that applies, and does the clinical picture actually meet it?[9]
  • Does a personal or family history of malignancy change the calculus, given the cohort associations between circulating IGF-1 and cancer risk?[13]
  • Given that hypoglycemia is the adverse event most consistently reported with the approved parent molecule, and that this analog was engineered to evade the binding proteins that buffer free IGF-1, what monitoring would detect a problem early?[8]
  • If competing in a tested sport, what does the current prohibited list say, and what are the consequences of a positive finding?[1]

A clinician who answers "there is no human literature on this molecule at all" is describing the evidence base accurately, not being dismissive.

Evidence by claim

Grades describe how strong the evidence is; the line under each grade describes what kind of studies it is. How we grade evidence.

Muscle growth, strength, or recovery benefit in humans
Anecdotal reports only review

No human evidence exists. No published randomized trial, controlled study, open-label series, or case report has administered IGF-1 LR3 to a person and measured muscle mass, strength, body composition, injury recovery, or any other outcome. This is not a case of weak or contested evidence; it is an empty literature. A 2026 review of performance-enhancing peptides acting on the growth-hormone/IGF-1 axis describes exactly this pattern — self-administration running well ahead of clinical evidence — and a 2026 review of peptides marketed for musculoskeletal injury and athletic performance characterizes the human safety and efficacy data for unapproved compounds in this class as scarce.

[10] [11]

Greater potency than native IGF-1 in cell culture
Animal studies only in vitro

This is the analog's best-established property, and it is an in vitro one. Long R3 IGF-I carries an arginine substitution at position 3 and a 13-amino-acid N-terminal extension, which together sharply reduce its affinity for the IGF-binding proteins that sequester native IGF-1. In L6 myogenic cell cultures, recombinant IGFBP-3 inhibited IGF-I-stimulated proliferation and differentiation while long-R3-IGF-I was comparatively resistant to that inhibition. Recombinantly expressed and purified LR3 IGF-1 shows cell-proliferation bioactivity comparable to an IGF-1 standard. Both results are about cells in dishes.

[4] [5]

Tissue and organ growth in animals
Animal studies only animal

Animal work reports selective, tissue-level effects rather than the whole-body anabolism the compound's reputation implies. Seven-day infusion in guinea pigs raised the fractional weight of adrenals, gut, kidneys and spleen without stimulating overall growth, and reduced plasma IGF-I, IGF-II and binding-protein concentrations. In rats, seven-day infusion increased jejunal glucose uptake by up to 69% per centimetre of intestine, which the authors attributed to increased mucosal mass rather than to upregulated transporters, and the functional gain was smaller than the growth response. In neonatal calves, subcutaneous administration modulated the somatotropic axis and lowered native IGF-I and growth hormone. Gut, kidney and adrenal growth in a rodent is not a muscle-hypertrophy finding.

[2] [6] [7]

Neurological or cognitive benefit
Animal studies only animal

One long-duration animal study is directly informative and its headline result is negative. Male 5XFAD mice given intranasal long R3 IGF-1 for seven months showed improved body composition and some favorable changes in amyloid plaque morphology in the cerebral cortex, but no significant improvement across multiple assays of behavior and memory. The authors concluded the data do not support the analog as a monotherapy. It is a transgenic mouse model of Alzheimer's disease, not a study of cognition in healthy adults.

[3]

Evidence transferred from mecasermin, the approved IGF-1 product
Anecdotal reports only review · human observational

Recombinant human IGF-1 (mecasermin) is FDA-approved for severe primary IGF-1 deficiency and for growth hormone gene deletion with neutralizing antibodies, and registry data report near-adult height outcomes in treated patients. None of that is evidence about IGF-1 LR3. Mecasermin is native human IGF-1; the analog carries a substitution and an N-terminal extension that were introduced specifically to change how it interacts with binding proteins, which changes its distribution, clearance and potency. The approved product's trials, label, and outcome registry describe a different molecule given to a specific pediatric deficiency population for a growth endpoint. Reading across from one to the other is not a conservative inference; it is a different compound.

[8] [9]

Long-term safety in humans
Anecdotal reports only review · human observational

Nothing is known. No human has been followed on this analog in any published study for any length of time, so there is no basis for a statement about long-term safety in either direction. The nearest relevant literature is the adverse-event record of the approved parent molecule, which is a different compound in a different population, and prospective cohort associations between endogenous IGF-1 and cancer risk, which describe people taking nothing at all.

[8] [13]

FOR RESEARCH PURPOSES ONLY

Typical protocol range in the research

  • Seven-day continuous subcutaneous infusion in female guinea pigs, with organ and carcass weights as the endpoints

    120 micrograms per animal per day of long R3 IGF-I; fractional weights of adrenals, gut, kidneys and spleen rose while overall body growth did not [2]

  • Single intramuscular administration in rats, in an anti-doping study whose purpose was to measure how long the analog and its degradation products stay detectable

    100 micrograms per kilogram of body weight; unchanged long R3 IGF-I disappeared from the sampled matrix within about four hours, while N-terminal degradation products persisted for up to sixteen [1]

  • Seven-day continuous subcutaneous infusion by mini-pump in rats, with intestinal absorption and mucosal mass as the endpoints

    The published rat infusion range for the analog, reported as a comparator against native IGF-I rather than as an established dose for anything [6]

Every figure above comes from an animal experiment whose endpoint was an organ weight, an absorption measurement, or an analytical detection window. No published human study has ever administered IGF-1 LR3 at any dose, for any purpose, so no human dose is established and none is reported here. The milligram and microgram figures that circulate in community discussion have no published study behind them.

Ranges are what published research reports, not a recommendation. PHL does not prescribe, and nothing here is personalized to you.

Side effects & safety signals

  • No human safety data of any kind

    Not established · There is no published clinical trial, case series, or registry of IGF-1 LR3 in humans, so there is no adverse-event profile to describe. An anti-doping review notes that IGF-1 analogs of this class were never approved for use in humans while remaining readily available for bodybuilding use, which is precisely the combination that produces no safety literature. Absence of reported harm here is absence of observation, not evidence of safety.

    [1] [11]

  • Hypoglycemia, documented for the parent molecule

    Reported as a common adverse event with mecasermin, a different molecule · This entry is about the parent molecule, not the analog. Recombinant human IGF-1 (mecasermin) is an approved treatment for severe primary IGF-1 deficiency, and hypoglycemia has been the adverse event most consistently reported with it. IGF-1 LR3 was engineered specifically to evade the binding proteins that buffer circulating IGF-1, so the biological reason to expect this effect is if anything stronger for the analog than for the parent. No study has measured it for the analog. A history of diabetes, prediabetes, or use of any glucose-lowering medication is a provider-discussion flag.

    [8]

  • Sustained IGF-1 receptor signaling and the malignancy question

    Not measured for this analog · Large prospective cohort work links higher circulating IGF-1 concentration to the risk of several cancers, most consistently prostate cancer. That work describes naturally varying IGF-1 in people taking nothing and is not a measured risk of this or any analog. It is, however, the reason a personal or family history of malignancy belongs in a clinician conversation about anything that raises IGF-1 receptor signaling.

    [12] [13]

  • Suppression of the endogenous somatotropic axis in animals

    Observed in treated calves · In neonatal calves, subcutaneous long R3 IGF-I lowered native IGF-I and decreased circulating growth hormone while raising IGFBP-2. In infused guinea pigs, the analog was associated with reduced plasma IGF-I, IGF-II and binding-protein concentrations. Both are animal observations of the axis responding to an exogenous agonist. What the same exposure would do to a hormonally normal adult human has not been studied.

    [7] [2]

  • Unverified identity and documented degradation of circulating material

    Not quantified · When an anti-doping laboratory characterized preparations circulating for bodybuilding use, it reported abundant signs of lower-quality, oxidized peptide forms, and had to monitor both the native and the mono-oxidized analog to detect the substance reliably. With no approved manufacturer there is no assay standard and no release specification, so nothing guarantees that a vial carrying this name holds the molecule the name denotes, in the form the name denotes.

    [1]

  • Prohibited in tested sport

    Standing status · IGF-1 and its analogs, long R3 IGF-I named among them, are prohibited substances in sport, and validated mass-spectrometry methods now detect the analog and its N-terminal degradation products. This is an enforceable status rather than a theoretical one. Any athlete in a tested sport should confirm the current year's prohibited list rather than rely on this page.

    [1] [10]

Published lists are never exhaustive, so report anything unexpected to a licensed provider.

Storage, handling & reconstitution

Lyophilized storage
Lyophilized IGF-1 LR3 is conventionally kept refrigerated at 2–8 °C and protected from light, with freezing used for long-term holding. That convention comes from general lyophilized-protein practice and from the way the analog is handled as a laboratory reagent, not from a published stability study of this molecule. No such study exists.
Reconstituted storage
Once in solution, recombinant proteins of this class are conventionally refrigerated at 2–8 °C, protected from light, and treated as short-dated rather than indefinitely stable. Repeated freeze-thaw cycling is conventionally avoided. No published study establishes a solution shelf life for IGF-1 LR3.
Reconstitution diluent
The conventional diluent for lyophilized research proteins in this class is bacteriostatic water: sterile water preserved with 0.9% benzyl alcohol. Dilute acetic acid is used in some laboratory reagent protocols because the analog dissolves more readily at low pH, which is a laboratory handling convention rather than a clinical one.
Reconstitution & handling
Conventional handling: sanitize the stopper before piercing it, add the diluent slowly down the inside wall of the vial rather than directly onto the powder, and let it dissolve on its own. Swirl gently if needed; never shake, because proteins of this size are shear-sensitive. A properly reconstituted solution is clear; anything cloudy, discolored, or carrying visible particulate is discarded. PHL does not publish volume or unit calculations, because those are dosing decisions and dosing decisions belong with a licensed clinician.
Handling notes
IGF-1 LR3 has no approved manufacturer, so there is no label, no assigned beyond-use date, and no lot-level stability data standing behind any storage claim. An anti-doping laboratory that characterized preparations circulating for bodybuilding use reported abundant signs of lower-quality, oxidized peptide forms in them, which is a reminder that degradation of this analog is a real and documented phenomenon rather than a theoretical one. Treat everything above as convention, not specification.

The how-to guides cover the conventions behind these fields, and what the published stability data does and does not establish: Storage, Reconstitution, Handling.

Questions for your provider

Bring this page to a licensed provider. A provider can order labs, review your medications and history, and tell you whether anything here is relevant to your situation. This page can't. Peptide Health Lab does not prescribe and does not sell peptides.

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Citations

13 sources · every identifier checked against PubMed

Before you act on any of this

This page is educational only and is not medical advice. It does not diagnose, treat, or prescribe. Review it with a licensed provider before making any health decision. Peptide Health Lab does not sell peptides.

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