Peptide Library · checked July 31, 2026

IGF-1 LR3

IGF-1 LR3 is a distinct experimental IGF-1 analogue—not prescription mecasermin. PepCurrent found animal, cell, and product-analysis records—but no controlled human outcome evidence for muscle, recovery, performance, cognition, or “anti-aging.”

PreclinicalAnimal, cell, or mechanistic evidence without adequate human outcomes.How labels work →

TL;DR

The lowdown

Four answers first. The source record follows.

01 · Identity

What is it?

Long-(Arg3)insulin-like growth factor-I; aliases include IGF-1 LR3 and Long R3 IGF-I

02 · Human evidence

What do humans show?

No controlled administered-human clinical outcome study of exact IGF-1 LR3 identified in the July 2026 pass

03 · U.S. status

Where does FDA stand?

Exact-substance U.S. approval status not established; approved mecasermin evidence does not transfer

04 · Risks

What is known—and not?

PepCurrent located no FDA-approved IGF-1 LR3 prescribing information and no exact-substance human clinical safety study. Its complete human adverse-effect, contraindication, and interaction profile remains uncharacterized.

U.S. status · July 31, 2026

Approval, compounding, product, sport.

FDA approval: The reviewed source does not establish an FDA-approved product; database silence is not permission or a broader legal conclusion.
U.S. federal record: Exact-substance U.S. approval status not established; approved mecasermin evidence does not transfer
Product identity: A 2010 analytical case identified a His-tagged Long R3 IGF-I protein in one black-market injection vial. The analyzed material included a laboratory purification tag and linker, and the paper did not establish its effects in people. One vial cannot establish another product’s sequence, tags, concentration, purity, sterility, stability, or storage history.
Sport: No WADA status recorded in the reviewed source.

This reports the dated federal and sport record. It does not determine whether a particular product or transaction complies with state or federal law, and it is not legal advice.

What it is

IGF-1 LR3 is Long-(Arg3)insulin-like growth factor-I, registered by FDA under UNII M9L22Y19H9. Long R3 IGF-I and insulin-like growth factor long chain R3 are aliases. Mecasermin is not.

Mecasermin is recombinant human IGF-1 and the active ingredient in INCRELEX. Its approval, indication, dosing, warnings, adverse reactions, and pharmacokinetics cannot be borrowed for IGF-1 LR3.

Why people care

IGF-1 LR3 is discussed for muscle gain, recovery, performance, and “anti-aging,” often by borrowing language from prescription mecasermin or from biological activity in animals and cells. The central reader-protection issue is identity: IGF-1 LR3 and mecasermin are not the same FDA substance, and the approved INCRELEX record cannot be transferred to IGF-1 LR3.

What humans actually show

No controlled administered-human clinical outcome study of exact-substance IGF-1 LR3 for muscle gain, recovery, performance, cognition, anti-aging, or another clinical outcome was identified in the July 27 PubMed and ClinicalTrials.gov searches. Human-cell experiments and product analysis are not administered-human benefit evidence.

Mechanistic and nonhuman evidence

1997 pig study: Long R3 IGF-I reduced average daily gain, food intake, and several circulating measures in a short infusion experiment. Porcine growth hormone coadministration did not produce an interactive effect on growth performance. Livestock physiology does not establish human muscle benefit or combination safety.
1995 guinea-pig study: Long R3 IGF-I increased fractional weights of several organs but did not significantly increase overall body-weight gain or change carcass composition. Organ-weight findings are not human muscle gain.
2025 5XFAD mouse study: Long R3 IGF-I altered amyloid-plaque measures in male mice but did not significantly preserve cognition in the reported assays. Plaque remodeling is not a clinical benefit.
Cell studies: Long R3 IGF-I has been used as a laboratory probe in prostate-cancer and Chinese hamster ovary cells. Reported telomerase or receptor-signaling changes establish activity in specific cell systems, not a human benefit or a quantified human cancer risk.

FDA and U.S. status

A 2020 FDA warning letter named IGF1-LR3 among substances used by one inspected compounder and said the named substances were not components of an FDA-approved human drug or on the 503A Bulks List at that time. That is a firm-specific enforcement record.

Exact Drugs@FDA searches for IGF-1 LR3 and Long-(Arg3)insulin-like growth factor-I returned no matches on July 27, 2026. PepCurrent records the search result but does not convert database silence into an FDA approval, nonapproval, legality, or product-specific conclusion. FDA separately identifies mecasermin/INCRELEX as approved for a narrow pediatric growth-failure indication; that approval does not transfer.

Risks and warning limits

INCRELEX warnings apply to mecasermin as defined in that product’s label. Copying them onto IGF-1 LR3 would falsely imply that the substances, products, pharmacokinetics, and labeled uses are the same. Conversely, the lack of an IGF-1 LR3 label or human safety study is not evidence of safety.

What remains unknown

Human pharmacokinetics, efficacy, adverse effects, contraindications, and interactions for exact IGF-1 LR3.
Whether any product offered under the name matches the FDA substance identity or a study material.
Whether animal or cell findings translate to a patient-important human outcome.
How a His-tagged or otherwise modified material differs from untagged Long R3 IGF-I in people.

Product identity and quality limits

A 2010 analytical case identified a His-tagged Long R3 IGF-I protein in one black-market injection vial. The analyzed material included a laboratory purification tag and linker, and the paper did not establish its effects in people. One vial cannot establish another product’s sequence, tags, concentration, purity, sterility, stability, or storage history.

What has been studied together

The 1997 pig study examined Long R3 IGF-I with porcine growth hormone and reported no interactive effect on growth performance in that model. This is preclinical coadministration evidence only. PepCurrent identified no direct human interaction study of IGF-1 LR3. Missing human evidence does not establish compatibility with growth hormone, insulin, mecasermin, another peptide, or any medicine.

What people are hearing

“IGF-1 LR3 is basically prescription IGF-1.” FDA maintains separate substance identities for Long-(Arg3)insulin-like growth factor-I and mecasermin.
“Animal growth or cell signaling proves human muscle benefit.” Animal growth, organ-weight, plaque, and cell-signaling outcomes are not controlled human clinical outcomes.
“A vial labeled IGF-1 LR3 matches the research material.” One analytical case found a His-tagged protein in one black-market vial, illustrating product uncertainty rather than authenticating the market.

Questions readers raise

Readers ask whether IGF-1 LR3 can be treated like INCRELEX, whether animal growth findings imply human muscle gain, and whether an “IGF-1” label verifies the analog inside. These are recurring questions, not evidence. PepCurrent has not published anecdotal theme counts or public user reviews for this profile.

What would change this answer

A registered, well-reported controlled human trial administering a fully characterized IGF-1 LR3 product.
Product-specific pharmacokinetic, adverse-event, contraindication, and interaction evidence.
Independent analytical evidence establishing the exact material used in a study or product.
Exact-product FDA action or final prescribing information.

Sources and records

Boundary: PepCurrent explains public evidence and regulatory records. We do not evaluate individual products, recommend use, name vendors, or provide protocols.