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Growth & GHPeptideEvidence C3 cited

IGF-1 LR3

Insulin-Like Growth Factor-1 Long Arginine 3

aka Long R3 IGF-1 · LR3-IGF-1 · insulin-like growth factor 1 long R3

A synthetic IGF-1 analog with extended half-life, researched for muscle hyperplasia and cellular proliferation.

Half-life
20 h
clinical
Tmax
2 h
Route
Subcutaneous injection

Sequence

One-letter83 residues

MFPAMPLSSLFVNGPRTLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA

Read this before quoting the sequence
83 residues. Long [Arg3]-IGF-I is defined by Francis et al. 1992 (PMID 1378742) as '[Met1]-pGH(1-11)-Val-Asn-[Arg3]-IGF-I': a 13-residue N-terminal extension consisting of the first 11 amino acids of methionyl porcine growth hormone plus Val-Asn, fused to human IGF-I in which Glu3 is replaced by Arg. Mature porcine somatotropin begins FPAMPLSSLF (UniProt P01248, chain 27-216), so the extension is MFPAMPLSSLF-V-N = MFPAMPLSSLFVN. Mature human IGF-I is GPETLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA (UniProt P05019, chain 49-118, 70 aa); Glu3>Arg gives GPRTL... . The construction is independently corroborated by Bryant et al. 1996 (PMID 8919033), which reports pepsin cleaving 'the Leu10-Phe11 bond in the N-terminal extension peptide' - positions 10 and 11 of MFPAMPLSSLFVN are indeed Leu and Phe. This string is assembled from those primary sources rather than copied from a single database record; there is no UniProt, PubChem or FDA GSRS entry for LR3-IGF-I. Three intramolecular disulfides are retained from IGF-I.
Source ↗

Mechanism of action

IGF-1 LR3 binds to the IGF-1 receptor with high affinity, activating intracellular signaling pathways such as the PI3K/Akt pathway. This leads to increased protein synthesis and cell proliferation, particularly in muscle and bone tissues. The extended half-life allows for prolonged receptor activation compared to native IGF-1.

What the evidence actually shows

Grade C

There are limited human trials specifically on IGF-1 LR3. Most evidence comes from animal studies and extrapolation from IGF-1 research. Human trials are needed to confirm efficacy and safety, particularly long-term effects.

Regulatory status

Status
Not approved in any jurisdiction; supplied as a laboratory research reagent. No marketing authorisation identified.
Clinical stage
No human clinical development; published evidence is animal and in vitro.
WADA
Prohibited at all times (in- and out-of-competition), non-Specified. 2026 Prohibited List S2.3 'Growth factors and growth factor modulators' lists 'Insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues'.
UK
research_compound

In the UK, IGF-1 LR3 is not approved for medical use and is classified as a research compound. It is not licensed for human consumption.

Source ↗

Pharmacokinetics

Half-life
20 h
Tmax
2 h
Absorption
subcutaneous
Elimination
renal
Washout
14 days
Titration
Documented as required
Low-confidence pharmacokinetics
These figures are recorded as clinical rather than measured in a published PK study. Treat them as an order of magnitude. Anything downstream of them — accumulation, steady state, washout — inherits that uncertainty.

Dosing — what backs each figure

IGF-1 LR3 has no human dosing data whatsoever - no registered interventional trial and no published human administration study. The only in vivo dosing evidence is rodent, and the parent-compound trap here is mecasermin (INCRELEX), a different, FDA-approved molecule whose label must not be attributed to LR3.

PreclinicalAnimal studies — not a human dose

  • LONG R3 (LR3) IGF-I administered to C26 tumour-bearing and non-tumour-bearing mice in a cancer cachexia model, alone and combined with the ALK4/5 inhibitor SB431542; LR3 IGF-I limited loss of muscle mass but accelerated tumour growth

    mouse (CD2F1, C26 colon carcinoma cachexia model) · systemic injection (in vivo dosing arm of the study) · PMID 31285507

Animal doses do not convert to human doses by body weight alone. Route matters too — a compound dosed intraperitoneally in mice tells you little about subcutaneous use.

Commonly circulatedNot established by any study
Dose
Research literature cites ~20 to 50 mcg/day
Frequency
1-3x daily
Cycle
4-6 weeks· unsourced

Why this isn't evidence
A ClinicalTrials.gov intervention search for IGF-1 LR3 returns zero studies and no published human administration study was found, so the 20-50 mcg/day figure and the 4-6 week cycle are bodybuilding-forum convention, not research literature as the field claims.

This figure is shown because it is what circulates and what people search for — not because it is supported. Cycle lengths in particular tend to be convention copied between compounds rather than anything derived from a compound's own pharmacokinetics.

No established human dose
No approved label or completed human trial establishes a dosing regimen for this compound. Anything presented as a standard protocol for it — anywhere — is someone's convention rather than a finding.

Handling and storage

No compound-specific stability data exists
No compound-specific published stability data (temperature/duration for lyophilised or reconstituted material, light sensitivity, freeze-thaw tolerance) was located in any regulatory label, pharmacopoeial monograph or peer-reviewed source. Only generic lyophilised-peptide handling guidance exists, and generic guidance is not compound-specific; no specific figures are asserted here. LR3-IGF-I is a research reagent protein with no approved product. Kohler et al. 2010 (PMID 20675162) further found that a black-market 'IGF-1 LR3' injection vial actually contained His-tagged Long-R3-IGF-I, a biochemical research construct, so material sold under this name is not of a defined pharmaceutical quality. General peptide handling still applies — reconstitute gently, keep it cold, keep it dark — but any specific figure you see quoted for this compound elsewhere is someone's assumption, not a measurement.
→ Reconstitution walkthrough→ Reconstitution calculator

Safety

Commonly reported
  • ·Hypoglycemia
  • ·"Joint pain"
  • ·"Water retention"
Rarely reported
  • ·Increased risk of cancer
  • ·Cardiovascular issues
Contraindications
  • ·Active cancer
  • ·Pregnancy
  • ·Diabetes
Drug interactions
  • ·Insulin: May enhance hypoglycemic effects due to increased insulin sensitivity.

Hypoglycaemia, joint pain, organ growth with prolonged use

Reported combinations

Reported as synergistic
  • ·Creatine
  • ·"Branched-chain amino acids (BCAAs)"
Reported as antagonistic
  • ·Glucocorticoids

Combination claims in this dataset are largely unsourced and should be treated as folk knowledge until a citation appears beside them.

References (3)

Data provenance

Chemistry and citations on this page were checked against primary sources on 2026-08-14. Values that could not be verified were left blank rather than filled with a plausible guess.

Could not verify
molecularFormula, molecularWeight, casNumber, pubchemCid, sequence.threeLetter, storage.lyophilized, storage.reconstituted, storage.lightSensitive, reconstitution.solvent

Research use only
This profile is educational reference material. It is not medical advice, not a prescription, and not an endorsement of self-administration. Compounds discussed here are research chemicals and most are not approved for human therapeutic use.

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