IGF-1 LR3 is sold by research vendors and described on many ranking pages as a muscle compound. We read the papers, the drug label for its approved relative, and the vendor listings among the four we review to see what is on record. This page is not advice to use it. Vendors label it for laboratory research only.
What IGF-1 LR3 is
IGF-1 LR3, short for Long Arginine 3 IGF-1, is a modified form of insulin-like growth factor 1. The Core Power Peptides listing describes an arginine substitution at position 3 and a 13 amino acid extension at one end, and says the changes reduce binding to IGF-binding proteins. It is a research reagent. A 2023 paper that produced it in yeast reports that the purified LR3 showed cell proliferation activity comparable to standard IGF-1 and says it could serve clinical and scientific uses.
What has been published
We found cell and animal work and no published human trial of LR3. A 2025 mouse study gave it intranasally to a mouse model of Alzheimer's disease and reported improved body composition and no significant change in cognitive symptoms. That is a result in mice and says nothing about people.
A 2026 review from Poznan University of Medical Sciences lists IGF-1 LR3 among the unregulated growth hormone axis peptides sold as research compounds. It sorts them into evidence tiers running from regulatory-grade trial data to a complete absence of human studies, and says no regulator has approved them for physique or performance purposes. We read the abstract and not the full text, so we cannot say which tier it assigns LR3.
What anti-doping researchers found
A French anti-doping laboratory paper from 2021 states that LongR3 IGF-I and two related analogs are prohibited in sport, were never approved for use in humans, and are readily available as black market products for bodybuilding. It also reports abundant signs of lower quality, oxidized peptide forms in black market products. In rats, the intact LongR3 form disappeared within about 4 hours of an intramuscular injection, while two of the other analogs stayed detectable for up to 24 hours. The 2026 WADA Prohibited List, as reproduced by the Cologne laboratory, names IGF-1 and its analogues and mechano growth factors.
The approved relative is a different molecule
Mecasermin (Increlex) is recombinant human IGF-1, not LR3. Its label limits it to children with severe primary IGF-1 deficiency, or growth hormone gene deletion with antibodies to growth hormone, and lists severe hypoglycemia leading to seizures among its warnings. It also records postmarketing reports of malignant neoplasms in children and says the relationship to the drug is unknown. Nobody has published that LR3 does or does not behave the same way. We mention the label because it shows what regulators have recorded for this pathway.
What the listing says and what we found
Swipe the table sideways to see every column.
| Listing statement | Source on the page | What we found |
|---|---|---|
| Half-life of about 20 to 30 hours | None given | The anti-doping paper tracked the intact peptide in rats and lost it after about 4 hours. That is a different measurement, so we could not confirm the listing's figure either way. |
| 99% or higher purity, HPLC and MS/MS verified | The listing itself, with a COA 'available on request' | No certificate or lab name on the page. |
| Research applications include skeletal muscle hypertrophy and atrophy models | The listing itself | A description of research models. We found no human trial. |
Who lists it
Of the four vendors we review, Core Power Peptides () and American Peptides () list IGF-1 LR3. Peptides for Sale lists PEG-MGF but no IGF-1 LR3, and we found no IGF-1 product in Peptryn's product sitemap. Because the French paper found degraded forms in black market samples, the paperwork matters more here than for most compounds. Our guide to reading a COA explains what a certificate should name, and the Core Power Peptides review lists what we could not confirm for this vendor.
Frequently asked questions
What does the LR3 in IGF-1 LR3 mean?
Long Arginine 3. It refers to two changes to IGF-1: an arginine at position 3 and a 13 amino acid extension, which the vendor says reduce binding to IGF-binding proteins.
Is IGF-1 LR3 approved for human use?
A 2021 anti-doping paper says it was never approved for use in humans. The approved drug mecasermin is native IGF-1, a different molecule, for a pediatric condition. Check current FDA records.
Is IGF-1 LR3 banned in sport?
The 2026 WADA list, as reproduced by the Cologne laboratory, names IGF-1 and its analogues. Tested athletes should read the current list themselves.