Reviewed & approved by Dr. Nova Reyes · Last checked 2026-10-15. ← Back to Evidence Library

IGF-1 LR3: what the evidence says

At a glance

What it is: a lab-made, longer version of the body's own growth hormone helper, insulin-like growth factor 1 (IGF-1). "LR3" stands for "Long" plus a swapped amino acid (arginine at position 3). The changes make it bind less to the proteins that normally hold IGF-1 in check, so it stays active longer. It was made as a cell-culture reagent for laboratories. It is sold online for muscle growth and fat loss. R1, R2

Caution There is no human trial data for IGF-1 LR3. None. It has never been tested in people in any published study we could find. Everything known about it comes from cells and animals. Mecasermin (Increlex), the approved IGF-1 drug, is a different molecule. Its trial results do not apply to LR3.

What the evidence says: no human data. In growth-restricted fetal sheep it did not improve growth. In Alzheimer's-model mice it changed brain plaques but did not protect memory. No study tested muscle or fat benefits. R5, R6

Biggest risks: low blood sugar (hypoglycemia), which can be severe enough to cause seizures with the approved IGF-1. There is also a theoretical cancer risk, because IGF-1 drives cell growth. And you can't know what's in the vial. R3, R7, R2

Claim Rating
Unknown Muscle growth, fat loss, recovery, "anti-aging" No human data (animal/lab only)
Animal Animal / lab evidence Cell-growth reagent; fetal sheep (no growth benefit) and Alzheimer's-model mouse (no memory benefit) studies R5, R6
Human Approved relative (mecasermin, Increlex) Not LR3. Approved for severe primary IGF-1 deficiency in children only R3, R4
Regulatory Not approved anywhere · not in any FDA 503A/503B nomination category · WADA 2026: banned at all times (S2.3, "IGF-1 and its analogues") R8, R9
Established human dose Unknown None for LR3

Evidence verdict: All claimed uses: No human data (animal/lab only) Card verdict: No human data (muscle & fat-loss claims untested in humans; engineered to resist normal IGF-1 binding)

This page reports what studies used. It is not dosing advice.

Legend: HUMAN data · ANIMAL / LAB data · UNKNOWN · UNVERIFIED: not yet confirmed against a primary source

What "No human data" means here: IGF-1 LR3 has been studied in cells and animals only. We found no published study of it in people (PubMed search, Oct 15, 2026).

What is it?

IGF-1 is a hormone made mainly in the liver when growth hormone signals it. It helps children grow and helps tissues build and repair. In the blood, most IGF-1 is held by binding proteins that control how much is active. IGF-1 LR3 is 83 amino acids long (natural IGF-1 is 70). It has an extra 13-amino-acid tail and one swapped amino acid. These changes mean binding proteins hold it much less, so more of it is free to act. R1

It was designed for growing cells in the lab, not for injection into people. One black-market vial tested by an anti-doping lab contained a version with a lab purification tag still attached, which "is usually produced for biochemical studies." R2

The approved IGF-1 drug: mecasermin (Increlex)

This section covers only mecasermin. It is not IGF-1 LR3, and its results do not transfer. - FDA: Increlex (BLA 021839, now held by Ipsen) approved Aug 30, 2005. EU: authorised Aug 2, 2007 under "exceptional circumstances" (current holder Esteve). Approved only for long-term treatment of growth failure in children with severe primary IGF-1 deficiency. R3, R4 - What its studies showed: five studies (76 children per EMA; the FDA label pools 71), mostly without a placebo group. Growth averaged 2.8 cm/year before treatment, 8.0 cm in year 1 and 5.8 cm in year 2 (FDA label). Only one study (8 patients) had a placebo comparison. R3, R4 - Who paid: the studies were run by the companies developing the drug. Caution [UNVERIFIED: individual trial funders not checked]

Does it work?

Unknown For muscle, fat loss, recovery or anti-aging in adults: no human data. We found no published human trial of IGF-1 LR3 for any use.

Animal Animal studies: in growth-restricted fetal sheep (7 treated, 7 controls), a 1-week LR3 infusion did not improve growth. Insulin levels didn't differ, and blood amino acids fell R5. In a mouse model of Alzheimer's disease, LR3 sprayed in the nose changed amyloid plaques but "fails to preserve" memory R6. A change in a lab or biomarker measure is not a health benefit, and animal results often fail in people.

Is it safe?

There is no human safety data for IGF-1 LR3. The risks below come from the approved IGF-1 drug and from research on IGF-1 in general. Because LR3 is designed to be more freely active, these risks could be greater, but nobody has measured that. - Caution Low blood sugar (hypoglycemia): IGF-1 lowers blood sugar like insulin does. With Increlex, 42% of children had hypoglycemia at least once. 5 had severe episodes, and 4 had seizures from it. The label says to give it with a meal or snack. R3 - Caution Cancer (theoretical): IGF-1 drives cell growth and survival. Increlex must not be used (it is contraindicated) by anyone with cancer or a history of it, and "several cases of malignant neoplasia have been observed" in children treated with it. R3 Across 21 studies, people with higher natural IGF-1 levels had modestly higher risk of prostate and premenopausal breast cancer (odds ratios of 1.49 and 1.65, comparing people at the 75th percentile of IGF-1 levels with people at the 25th percentile). That is an association, not proof that taking IGF-1 causes cancer. R7 - Caution Other risks on the Increlex label: severe allergic reactions (anaphylaxis), raised pressure in the skull, enlarged tonsils and adenoids, hip problems in children, worsening scoliosis. R3 - Dropouts vs placebo: no placebo-controlled human data exist for LR3. Unknown

What we don't know

Is it legal?

What's in the vial?

There is no approved IGF-1 LR3 product, and a vial of it is not Increlex. Gray-market vials have no quality control. They could contain the wrong compound, the wrong amount, lab-grade material not meant for injection, impurities or bacterial toxins, or be fake (counterfeit). R2 We test retail vials blind under the Open Peptide Standard. See results at /tests/. A passing test covers one batch, tested on one date. It does not mean the compound itself is safe.

What do users report?

Self-report, not evidence.

Unknown TBD. We'll only list this once we can cite a public source.

Study details
R5, R6 Animal Animal studies (selected)
Study Animals Reported Citation
White 2025 Growth-restricted fetal sheep, LR3 infusion (7 vs 7) Did not improve growth; insulin unchanged; amino acids fell PMID 39679943
Engel 2025 Alzheimer's model mice, intranasal LR3 Plaque changes; memory not preserved PMID 39610283

No human studies exist to tabulate.

R3, R4, R8, R9 Label and regulatory (as of Oct 15, 2026)
Full reference list (PMIDs verified on PubMed, Oct 15, 2026)
  • R1 Francis GL, et al. J Mol Endocrinol. 1992;8(3):213-23. doi:10.1677/jme.0.0080213. PMID 1378742 (Long [Arg3]-IGF-I: a 13-amino-acid N-terminal extension plus Glu3→Arg).
  • R2 Kohler M, et al. Growth Horm IGF Res. 2010;20(5):386-90. doi:10.1016/j.ghir.2010.07.001. PMID 20675162.
  • R5 White A, et al. Am J Physiol Endocrinol Metab. 2025. doi:10.1152/ajpendo.00259.2024. PMID 39679943.
  • R6 Engel MG, et al. J Alzheimers Dis. 2025. doi:10.1177/13872877241299056. PMID 39610283.
  • R7 Renehan AG, et al. Lancet. 2004;363(9418):1346-53. doi:10.1016/S0140-6736(04)16044-3. PMID 15110491.

Disclaimer

This page is for education and harm reduction. It is not medical advice and not a recommendation to use IGF-1 LR3, which has never been tested in people. Talk to a clinician you trust, especially if you have diabetes or take blood-sugar medicines, have or have had cancer, or are a tested athlete. Seek care right away for shakiness, sweating, confusion or seizures, and report problems to FDA MedWatch (https://www.fda.gov/safety/medwatch).