Is IGF-1 LR3 FDA-approved, and what does the research show?

What is IGF-1 LR3?

IGF-1 LR3 is an engineered form of IGF-1, the hormone the liver and other tissues release when growth hormone signals them ¹¹. Its makers kept the IGF-1 sequence, replaced the glutamic acid at position 3 with arginine, and added a 13-amino-acid extension derived from pig growth hormone at the front ¹, ². The name is short for "Long [Arg3]-IGF-I" ¹.

The changes make it bind the body's IGF-binding proteins far less than IGF-1 does, so more of it stays free to act on cells ¹, ⁶. It was made in bacteria as a research reagent for studying how IGF-1 acts ¹. It is not mecasermin, the FDA-approved drug, which is recombinant human IGF-1 with the natural 70-amino-acid sequence ¹¹.

Is IGF-1 LR3 FDA-approved?

No. IGF-1 LR3 is not FDA-approved as a drug in its own right ³, ⁵. Drugs@FDA, as of November 9, 2026, holds no product under IGF-1 LR3 as a generic name, brand name or substance name ⁵. The approved IGF-1 drug is mecasermin, sold as Increlex, and it is recombinant human IGF-1 with the natural sequence, not the LR3 analogue ¹¹, ⁵. It is also absent from all three categories of FDA's list of substances nominated for compounding under section 503A, as updated May 14, 2026 ⁴.

In April 2020 FDA sent a warning letter to a Kentucky compounding firm that had compounded with IGF1-LR3 and twenty-one other substances ³. FDA wrote that the substance had "not been nominated for inclusion on the 503A bulks list" ³. Drugs compounded from such substances, FDA said, are not eligible for the exemptions that section 503A gives licensed pharmacies ³. The firm's products are "new drugs" that are "not generally recognized as safe and effective for their labeled uses" ³.

FDA's letter treated this firm's products as unapproved new drugs ³. The sources opened describe no lawful route to obtain it for use in people.

See the FDA status of every peptide, updated weekly.

How does IGF-1 LR3 work?

IGF-1 LR3 acts through the same receptor as IGF-1 itself ¹⁰. When IGF-1 binds the IGF-1 receptor on a cell's surface, the receptor switches on signaling pathways inside the cell ¹². Those pathways, PI 3-kinase and MAP kinase, drive cell proliferation, differentiation and survival ¹².

Shown in cells, IGF-1 LR3 was more potent than IGF-1 at stimulating protein and DNA synthesis in rat muscle cells that secrete IGF-binding proteins ¹. In cells that secrete none, it was less potent than IGF-1 ¹. The difference is its weak hold on those binding proteins, which in the body carry and restrain IGF-1 ¹, ⁶. It binds the receptor itself about three times less well than IGF-1 does ⁶. A 2026 review says its downstream signaling is "presumed" to be comparable to IGF-1's, because it engages the same receptor and no human study has measured it ¹⁰.

What does the research show?

No human studies were found. A 2026 narrative review of growth-hormone-axis peptides, published in Frontiers in Endocrinology, placed IGF-1 LR3 in its lowest evidence tier, with "no peer-reviewed human studies" ¹⁰. A search of ClinicalTrials.gov on November 9, 2026, returned no trial of IGF-1 LR3 under any of its names ¹³. What follows is animal and cell work.

Studied in animals for growth: rats were made catabolic with the steroid dexamethasone and infused for seven days ⁶. IGF-1 LR3 was about 2.5 times as potent as IGF-1 at restoring body weight and nitrogen retention ⁶. IGF-1 and especially its analogues, IGF-1 LR3 among them, increased gut weight by up to 45 percent ⁶.

In guinea pigs infused for seven days, IGF-1 LR3 enlarged the adrenals, gut, kidneys and spleen relative to body weight, but overall growth did not increase ⁹. In finisher pigs, a four-day infusion did the opposite of what the rat work suggests ⁸. Daily weight gain and food intake fell, and plasma growth hormone, IGF-1, IGFBP-3 and insulin all dropped ⁸.

Studied in animals for Alzheimer's disease: male mice bred to develop amyloid plaques were given IGF-1 LR3 into the nose for seven months ⁷. Treatment improved body composition and reduced filamentous plaques in the cortex, but did not significantly alter the mice's memory or behavior on multiple tests ⁷. The authors concluded the data "do not support LR3 as a monotherapy" ⁷. The review's literature search, which ran to January 2026, found no peer-reviewed human study of IGF-1 LR3 ¹⁰. ClinicalTrials.gov held no registered trial of it on November 9, 2026 ¹³.

What are the side effects?

No human study documents the side effects of IGF-1 LR3, because none exists ¹⁰. In animals, the documented effects are the ones above: enlarged organs in guinea pigs and rats, and in pigs less eating and lower growth hormone, IGF-1 and insulin ⁶, ⁸, ⁹. The 2026 review lists two concerns for IGF-1 analogues as a class, neither measured in people taking IGF-1 LR3 ¹⁰. One is low blood sugar: adverse effects reported in off-label settings often center on insulin-like activity, which the review calls biologically plausible, though many such reports come from non-clinical sources ¹⁰. The other is theoretical: stimulation of cell growth in tissues prone to it, because the receptor it activates drives cell division ¹⁰.

The nearest human evidence is FDA's label for mecasermin, the approved recombinant IGF-1, which is a different molecule ¹¹. That label warns of severe hypoglycemia leading to seizures and lists malignant neoplasia among its contraindications ¹¹. Hypoglycemia occurred in 42 percent of the 71 children with primary IGF-1 deficiency in its clinical studies ¹¹.

Product quality is a separate risk. Anti-doping researchers reported in 2010 that a black-market injection vial held "His-tagged" Long-R3-IGF-I, a form with a purification tag still attached that is "usually produced for biochemical studies" ¹⁴. They wrote that the effects of that form in humans "have not been elucidated or described" ¹⁴. The 2026 review notes that product composition in unregulated supply chains is uncertain ¹⁰.

In sport

WADA, the World Anti-Doping Agency, does not name IGF-1 LR3 on its 2026 Prohibited List ¹⁵. It lists "Insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues" under S2.3, "Growth factors and growth factor modulators" ¹⁵. Class S2 is prohibited at all times, in and out of competition, and all of its substances are non-Specified Substances ¹⁵. IGF-1 LR3 is an analogue of IGF-1 ¹, ¹⁰.

The list's opening class, S0, covers substances not addressed by any later section of the list and with no regulatory approval anywhere. It reads: "Any pharmacological substance which is not addressed by any of the subsequent sections of the List and with no current approval by any governmental regulatory health authority for human therapeutic use (e.g. drugs under pre-clinical or clinical development or discontinued, designer drugs, substances approved only for veterinary use) is prohibited at all times" ¹⁵. FDA has not approved IGF-1 LR3 ⁵, and the 2026 review records no regulatory approval of it for physique- or performance-related indications ¹⁰.

What JumpstartMD offers

JumpstartMD does not prescribe IGF-1 LR3. Our peptide library covers it so you have the facts on its FDA status and the evidence, current as of November 9, 2026.

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Compounded medications are not FDA-approved, and FDA does not review their safety, effectiveness, or quality before they are marketed. A licensed clinician decides after an evaluation whether a peptide is appropriate for you, and not every patient will qualify.