SoluneFit

Peptide library

IGF-1 LR3

Not FDA-approved Evidence grade D — animal or in-vitro data only Updated 2026-10-20

This page describes published research and public regulatory records. It is not medical advice. SoluneFit does not sell, supply, or recommend any compound. The SoluneFit app includes a private, on-device tracker for people who want a record of what they and their clinician have already decided — the app neither suggests compounds nor doses.

Also known as: Long R3 IGF-1, LR3IGF-I, Long-[Arg3]-IGF-I, LongR3-IGF-I.

Regulatory status

Not approved: Drugs@FDA has no application for it [7]; it is a research reagent. The nearest approved human IGF-1 is mecasermin (Increlex), approved only for severe primary IGF-1 deficiency in children [4]. IGF-1 and its analogues are WADA-prohibited at all times (S2.3) [6].

What it is

Recombinant IGF-1 analogue (human IGF-1 with Glu3→Arg, fused to an N-terminal extension of the first 11 amino acids of porcine GH plus Val-Asn).

An engineered form of insulin-like growth factor 1 made as a cell-culture reagent. Changing residue 3 and adding an N-terminal extension makes it bind IGF-binding proteins much less, so more of it is free to act; it has been studied only in cells and animals and has no human data or approved use.

What the published research shows

Cell-culture and animal work only (rats, pigs, marmoset monkeys); no published human study found.

Published human studies and reports (these describe trial populations, not SoluneFit claims):

  • Cell culture (Francis 1992): In L6 rat myoblasts and other cell lines that secrete IGF-binding proteins, Long [Arg3]-IGF-I was more potent than native IGF-I at stimulating protein and DNA synthesis; in cells without binding proteins it was less potent, showing that its extra potency comes from escaping the binding proteins.
  • Catabolic rats (Tomas 1992): Given by SC osmotic pump to dexamethasone-treated rats for 7 days, LR3IGF-I was about 2.5-fold more potent than IGF-I at reversing weight and nitrogen loss despite binding the IGF-1 receptor 3-fold less well.
  • Pigs and marmosets (Tomas 1997): Single bolus doses of 20 and 50 µg/kg in pigs: IGF variants lowered glucose 2-3 times more potently than IGF-I and for longer (4-8-fold more cumulative hypoglycaemia over 4 h), even though they are cleared from blood faster.

Mechanism, as reported

Activates the IGF-1 receptor (it binds the receptor about 3-fold less well than IGF-1) but escapes the IGF-binding proteins that normally hold IGF-1 in check, so in animals it is 2-3 times more potent for growth and glucose lowering and its glucose-lowering lasts longer.

Practical record

  • Studied routes: subcutaneous.
  • Typical supply: Sold as a cell-culture reagent and as lyophilised vials on the research-chemical market; no human-grade product exists.

Safety signals on record

  • Reported adverse events: No human data. In animals its main acute effect is hypoglycaemia, stronger and longer-lasting than native IGF-1; in pigs it also reduced growth, GH and the body's own IGF-1 production. The approved IGF-1 drug mecasermin carries label warnings for severe hypoglycaemia (with seizures), intracranial hypertension, lymphoid tissue overgrowth and postmarketing reports of malignant neoplasms in children.
  • Contraindications: None established (no label). For reference, mecasermin is contraindicated with closed epiphyses, active or past malignancy, and hypersensitivity.
  • Interactions: None documented. By analogy with IGF-1, additive glucose lowering with insulin or other antidiabetic drugs would be expected (not studied).
  • Notes: Increlex is the nearest human reference: its terminal half-life after a single SC dose in children with primary IGF-1 deficiency is about 5.8 h, but that is native IGF-1, which is held by binding proteins; LR3 binds them poorly and was cleared faster in animals, so the Increlex figure does not apply. No human half-life for LR3 is published (not established).

Sources

  1. Francis GL et al. Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. J Mol Endocrinol 1992;8(3):213-23 (1992)
  2. Tomas FM et al. Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. Biochem J 1992;282(Pt 1):91-7 (1992)
  3. Tomas FM et al. IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in pigs and marmoset monkeys. J Endocrinol 1997;155(2):377-86 (1997)
  4. INCRELEX (mecasermin) injection — US Prescribing Information (DailyMed, Eton Pharmaceuticals, published May 2026) (2026)
  5. Dunaiski V et al. Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs. J Endocrinol 1997;155(3):559-65 (1997)
  6. World Anti-Doping Agency. The 2026 Prohibited List (S2.3 IGF-1 and its analogues) (2026)
  7. Drugs@FDA: FDA-Approved Drugs database (no application for IGF-1 LR3 / Long R3 IGF-1; searched 2026-10-20) (2026)

General wellness education, not medical advice. Unapproved compounds have no established dosing, purity standard, or safety profile.

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