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IGF-1 LR3

Also known as Long R3 IGF-I · LR3-IGF-I · Long [Arg3]-IGF-I · LR3IGF-I

Not approved — research use onlyCPreclinical researchWhat this means

IGF-1 LR3 (Long R3 IGF-I) is a recombinant analogue of human insulin-like growth factor I with an arginine substitution at position 3 and a 13-amino-acid N-terminal extension, designed as a laboratory reagent that binds poorly to IGF-binding proteins. It has been studied in cell culture and animals, but no published human administration study was identified. It is not approved for human use, is distinct from the FDA-approved drug mecasermin, and is prohibited in sport; this entry is for research reference only.

US status
Not approved — research use only
Evidence
Grade C
Class
Recombinant insulin-like growth factor I analogue (N-terminally extended, Arg3-substituted fusion protein); research reagent
Studied in: Metabolic & insulin research · Muscle & body composition · Cognition & neuroprotection
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Unbranded reference vial illustrating IGF-1 LR3; not an actual product
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Key takeaways

  • IGF-1 LR3 is an engineered IGF-I analogue with an Arg3 substitution and an N-terminal extension, created as a laboratory reagent 1.
  • In rat myoblasts and other cells, the Long IGF-I analogues were more potent than native IGF-I, attributed mainly to reduced binding to IGF-binding proteins 1.
  • In pigs, LR3IGF-I lowered plasma glucose more potently and for longer than native IGF-I 2.
  • No published human administration study and no registered clinical trial were identified 6; the effects of a His-tagged form found in a black-market vial have not been described in humans 3.
  • WADA's 2026 List prohibits IGF-1 and its analogues at all times under S2.3 9.

Development stage

Where IGF-1 LR3 sits between laboratory work and regulatory approval.

  1. Preclinical (current)
  2. Phase 1
  3. Phase 2
  4. Phase 3
  5. Approved

Stage comes from the regulatory record and ClinicalTrials.gov studies naming the compound (for compounds approved nowhere, only completed trials or trials with posted results count) (checked 2026-10-24). A registered trial is not a result.

Mechanism of action

IGF-1 LR3 is an analogue of insulin-like growth factor I. Its design combines an Arg-for-Glu substitution at position 3 with a hydrophobic N-terminal extension 1.

Binding properties

The original characterisation reported that N-terminal IGF-I analogues show increased biological potency because of changes in their interaction with IGF-binding proteins (IGFBPs), rather than higher receptor affinity; in a cell line that does not secrete IGFBPs, Long [Arg3]-IGF-I was less potent than IGF-I 1.

Metabolic effects in animals

In pigs, variants with low IGFBP affinity, including LR3IGF-I, produced deeper and more prolonged reductions in plasma glucose than IGF-I, and LR3IGF-I alone was more potent than IGF-I in lowering plasma amino acids 2.

Research overview

Human research

No published study administering IGF-1 LR3 to humans was identified, and a ClinicalTrials.gov search returned no registered studies 6. A 2010 anti-doping analysis identified His-tagged Long R3 IGF-I in a black-market injection vial and stated that its effects in humans have not been elucidated or described 3. A 2026 clinical review places IGF-1 LR3 among unregulated performance-enhancing peptides and discusses dysglycaemia and theoretical mitogenic concerns for this class 5.

Animal research

In pigs, LR3IGF-I lowered plasma glucose with greater potency and duration than native IGF-I 2. In male 5XFAD mice, long-term intranasal LR3-IGF-1 improved body composition and some cortical amyloid plaque features but did not preserve behaviour or memory 4.

In-vitro research

In L6 rat myoblasts, Long IGF-I analogues stimulated protein and DNA synthesis and inhibited protein breakdown more potently than IGF-I; in BV-2 microglial cells, LR3-IGF-1 enhanced uptake of amyloid-beta 1-42 1,4.

Key studies

  1. Francis et al., J Mol Endocrinol (1992)
    Recombinant production and comparative bioassays of IGF-I fusion analogues
    Model: Cells (L6 rat myoblasts, H35 hepatoma cells, chicken embryo fibroblasts)

    Long [Arg3]-IGF-I was among the most potent analogues in cells secreting IGFBPs, but less potent than IGF-I in cells that do not secrete IGFBPs, indicating that reduced IGFBP binding drives the potency 1.

  2. Tomas et al., J Endocrinol (1997)
    Acute bolus comparisons with serial blood sampling over 4 hours
    Model: Animals (pigs; marmosets for other IGF-I variants)

    IGF-I variants including LR3IGF-I were 2- to 3-fold more potent than IGF-I for glucose lowering and produced roughly 4- to 8-fold greater cumulative hypoglycaemia; only LR3IGF-I was more potent than IGF-I for lowering plasma amino acids 2.

  3. Kohler et al., Growth Horm IGF Res (2010)
    Immunoaffinity purification, nano-UPLC and high-resolution mass spectrometry
    Model: Analytical (seized black-market product)

    The vial contained Long R3 IGF-I with a C-terminal His6 tag, consistent with a by-product of biochemical studies rather than a product made for injection 3.

  4. Engel et al., J Alzheimers Dis (2025)
    Intranasal treatment for 7 months versus vehicle, 19 to 27 mice per group
    Model: Animals (male 5XFAD mice) and BV-2 cells

    Treatment improved body composition and shifted cortical plaque morphology but did not significantly alter cognitive outcomes 4.

IGF-1 LR3 draw calculator

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Published adverse-event data

Reported in the cited trials or product labels. Frequencies apply to the stated population and do not transfer to other settings.

Emerging safety signals

  • In pigs, LR3IGF-I produced more potent and prolonged hypoglycaemia than native IGF-I, a mechanistic reason for concern about glucose lowering (animal evidence) 2. 2 (1997)
  • Black-market material has been found to contain a His-tagged research form of Long R3 IGF-I whose effects in humans are undescribed (analytical case report) 3. 3 (2010)
  • A 2026 clinical review lists dysglycaemia and biologically plausible but unproven mitogenic concerns for IGF-1-axis peptides used without regulatory approval (narrative review) 5. 5 (2026)

What is not known: No human pharmacokinetic, safety or efficacy data exist for IGF-1 LR3 in the sources reviewed 3,6; its human half-life is unknown. Animal and cell findings cannot be assumed to translate. Long-term effects, including on glucose regulation and on tissue growth, have not been characterised in any controlled study identified 2,5. Findings for mecasermin do not apply, because it is a different molecule 7.

Clinicians and researchers on video

YouTube videos about IGF-1 LR3 from clinicians and researchers. Their views, in their own words; not reviewed or endorsed by Amiravo. Compare what they say with the evidence above.

  • The IGF-1 Trade-Off: Performance vs. Longevity
    FoundMyFitness · 516K views
  • Every Popular Peptide Ranked | GLP-1, Growth Hormone, HCG, NAD+, IGF-1, Peptide Tier List
    Dr. Alex Tatem · 421K views

These creators are not affiliated with Amiravo and do not endorse Amiravo or any product linked on this site. Nothing here is medical advice. Video views counted on YouTube as of Oct 24, 2026.

Regulatory status

Status
Not approved for any human use. No registered clinical study was returned by a ClinicalTrials.gov search 6, and IGF-1 LR3 does not appear in any category of FDA's May 14, 2026 503A bulk drug substances list 8. It is a different molecule from mecasermin (INCRELEX), the FDA-approved recombinant human IGF-1 7. An anti-doping laboratory report describes Long R3 IGF-I as a product usually made for biochemical studies, found in a black-market injection vial 3.
United States (FDA)
Not approved. IGF-1 LR3 does not appear in any category of FDA's May 14, 2026 503A bulk drug substances list 8. The FDA-approved IGF-1 product is mecasermin (INCRELEX, application 021839), which is a different molecule 7.
Sport (WADA)
Prohibited at all times. Section S2.3, Growth Factors and Growth Factor Modulators, names insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues 9.

Status varies by country and changes over time. How we describe regulatory status.

Quality and testing notes

IGF-1 LR3 is a recombinant protein rather than a short synthetic peptide, so a certificate of analysis should show identity by intact mass and peptide mapping against the expected fusion sequence, correct disulfide pairing (IGF-I has three disulfides), SDS-PAGE and HPLC purity, host-cell protein and endotoxin content, and a bioassay where available [1]. A His-tagged variant has been found in black-market material, so mass data should exclude tag-containing forms [3].

How purity testing works · Reading a certificate of analysis

Check a IGF-1 LR3 certificate of analysis

Storage and handling

No approved-product storage instructions exist. Handling should follow the supplier's documentation; nothing here is a preparation or administration instruction.

Frequently asked questions

Is IGF-1 LR3 the same as mecasermin?
No. Mecasermin (INCRELEX) is FDA-approved recombinant human IGF-1 with the native sequence 7; IGF-1 LR3 has an Arg3 substitution and an N-terminal extension 1.
Has IGF-1 LR3 been tested in humans?
No published human administration study or registered clinical trial was identified 6.
Why was it made?
As a research reagent with reduced IGF-binding protein interaction, to study IGF-I action 1.
Is it banned in sport?
Yes. WADA S2.3 prohibits IGF-1 and its analogues at all times 9.
What has it done in animals?
In pigs it lowered blood glucose more potently and for longer than IGF-I 2.
Is it compoundable in the US?
It does not appear in any category of FDA's 503A bulk substances list 8.

Latest indexed research

No new studies were filed in the last sweep.

Search all studies on IGF-1 LR3 (PubMed, Europe PMC, ClinicalTrials.gov)

Listed by publication type from the index record. Inclusion is not an endorsement; open the source to read the findings.

Revision history

Meaningful changes to this entry, with dates and sources. Last reviewed Oct 23, 2026. Typo and layout fixes are not listed.

No recorded changes since the change log began on Oct 23, 2026.

References

  1. Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency J Mol Endocrinol. 1992
  2. IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in pigs and marmoset monkeys J Endocrinol. 1997
  3. Detection of His-tagged Long-R3-IGF-I in a black market product Growth Horm IGF Res. 2010
  4. 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 J Alzheimers Dis. 2025
  5. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration Front Endocrinol (Lausanne). 2026
  6. ClinicalTrials.gov API search for "long R3" IGF (no registered studies returned on 23 October 2026) ClinicalTrials.gov. 2026
  7. Drugs@FDA application records for mecasermin (INCRELEX, application 021839, original approval 30 August 2005) openFDA / Drugs@FDA. 2026
  8. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the FD&C Act (categories 1, 2 and 3; updated May 14, 2026) FDA. 2026
  9. International Standard: Prohibited List 2026 World Anti-Doping Agency. 2026

Last reviewed October 23, 2026 by the Amiravo editorial team.

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For research use only. Not for human or veterinary use. Not a drug, food, or dietary supplement. This page is educational and is not medical advice.

Unbranded reference vial illustrating IGF-1 LR3; not an actual product

Unbranded reference image. Amiravo does not produce, supply or sell this compound.

Specifications

Sequence
N-terminal 13-residue extension (the first 11 amino acids of methionyl porcine growth hormone followed by Val-Asn) fused to human IGF-I with Arg substituted for Glu at position 3 ([Met1]-pGH(1-11)-Val-Asn-[Arg3]-IGF-I)
Format
Lyophilized vial
Vial sizes seen
0.1 mg · 1 mg
Type
Single compound

Chemical identifiers are shown only when verified against PubChem.

Research stats

How much has been published, not how good it is.

PubMed records
102
Indexed as human research
35
Animal-only research
65
Randomized controlled trials
0
Registered trials
0
Trials with posted results
0
NIH-funded projects naming it
3
2006: 32007: 22008: 12009: 32010: 12011: 12012: 02013: 12014: 02015: 02016: 02017: 02018: 02019: 12020: 02021: 02022: 02023: 12024: 02025: 02026: 120062026
PubMed records per year (current year is partial).

Counts from title/abstract searches of PubMed, ClinicalTrials.gov, openFDA and NIH RePORTER, checked 2026-10-24. Names shared with other substances can inflate counts. FAERS reports are spontaneous and do not establish cause. Funding shows interest, not evidence. Method

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