IGF-1 LR3: what it is and what the evidence says
An analog of insulin-like growth factor, studied for its relationship with growth and muscle-repair signaling. It carries two changes that reduce its binding to the regulatory proteins, so it reaches the IGF-1 receptor free and activates it more potently than the native hormone.
Last reviewed: August 16, 2026 · How we verify this
The ground it plays on
Hormones work in axes: a signal from the brain tells a gland to release another hormone, and so on down the chain, with brakes that shut the process off. Intervening at one point has consequences both upstream and downstream. That is why this is the group where professional assessment stops being a recommendation and becomes essential.
What it is studied for
Muscle growth, recovery.
There is a distinction that almost always gets lost. A compound being studied for something is not the same as achieving it. And even where it works in a dish or in a mouse, that says little about whether it works in a person or whether the benefit is worth the risk. The section below therefore carries more weight than everything above it.
What the human evidence says
There are no published clinical trials of IGF-1 LR3 in people yet. The human data available come from native recombinant IGF-1 (mecasermin), given for severe primary IGF-1 deficiency, and from anti-doping detection studies.
The limitation that matters most
Its pharmacokinetics, efficacy, and safety in people remain to be studied. It was designed as a cell-culture reagent and studied in animals; because it binds the binding proteins only weakly, its action is more potent, and with recombinant IGF-1 hypoglycemia is a frequent adverse effect (26% of patients in the European Eu-IGFD registry).
Regulatory status
Not approved for use in people; it is a reagent for cell culture and research. The native molecule (mecasermin, Increlex) has been approved by the FDA since 2005 and by the EMA since 2007 for severe primary IGF-1 deficiency in children. Banned in sport at all times by WADA (section S2), which names IGF-1 and its analogues.
Status can change and varies by country. Always verify the rules in force where you live before drawing conclusions.
Cautions and context
Potent growth signal; metabolic and health profile is decisive and sensitive. It can lower glucose quickly and it activates a pathway that favors cell survival, so blood glucose and any cancer history are reviewed beforehand.
With diabetes, episodes of low glucose, a personal or family history of cancer, or while still growing, have a doctor assess it before you consider it.
What this page cannot give you
A reference page can take you this far. You know what IGF-1 LR3 is and where its research stands, which already puts you ahead of most readers. Four questions remain that no encyclopedia can answer for you, because the answers depend on your own situation:
- What would you measure beforehand, so that later you could tell whether anything actually changed?
- What would you watch along the way, and how consistently?
- What would you ask a professional, and in how much detail, so you do not walk out with a textbook answer?
- What would make you stop?
That is what the course is for
PeptiXtreme is ${CIF.LECCIONES} lessons that hand out no numbers. Each one ends with your starting point, what to watch along the way, the specific questions you take to a professional and the signals that mean stop. It includes per-module exams, a Certificate of Completion with a verifiable certificate ID, a Progress Tracker to follow how you are doing, and a human advisor you can actually write to.
See the course → Or measure your judgment, freeReferences
Every entry links to its record on PubMed, the US National Library of Medicine database. Open them and check. We would rather have a reader who verifies than one who takes our word for it.
- Detection of His-tagged Long-R3-IGF-I in a black market productpreclinical Growth Horm IGF Res · 2010 · PMID 20675162 →
- Biochemical markers of insulin-like growth factor-I misuse in athletes: the response of serum IGF-I, procollagen type III amino-terminal propeptide, and the GH-2000 score to the administration of rhIGF-I/rhIGF binding protein-3 complexhuman J Clin Endocrinol Metab · 2014 · PMID 24606087 →
- Frequency and Predictive Factors of Hypoglycemia in Patients Treated With rhIGF-1: Data From the Eu-IGFD Registryhuman J Clin Endocrinol Metab · 2023 · PMID 37579214 →
- Use of growth hormone, IGF-I, and insulin for anabolic purpose: Pharmacological basis, methods of detection, and adverse effectsreview Mol Cell Endocrinol · 2018 · PMID 28606865 →
- Insulin-like growth factor-I (IGF-I) misuse in athletes and potential methods for detectionreview Anal Bioanal Chem · 2013 · PMID 23934394 →
- Design and characterisation of long-R3-insulin-like growth factor-I muteins which show resistance to pepsin digestionpreclinical Growth Factors · 1996 · PMID 8919033 →
- Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pigpreclinical J Endocrinol · 1995 · PMID 7561636 →
- Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigspreclinical J Endocrinol · 1997 · PMID 9488001 →
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Frequently asked questions
What is IGF-1 LR3?
An analog of insulin-like growth factor, studied for its relationship with growth and muscle-repair signaling. It carries two changes that reduce its binding to the regulatory proteins, so it reaches the IGF-1 receptor free and activates it more potently than the native hormone. It is studied within the area of hormonal/sexual.
Is there human evidence for IGF-1 LR3?
There are no published clinical trials of IGF-1 LR3 in people yet. The human data available come from native recombinant IGF-1 (mecasermin), given for severe primary IGF-1 deficiency, and from anti-doping detection studies.
Is it approved by any health agency?
Not approved for use in people; it is a reagent for cell culture and research. The native molecule (mecasermin, Increlex) has been approved by the FDA since 2005 and by the EMA since 2007 for severe primary IGF-1 deficiency in children. Banned in sport at all times by WADA (section S2), which names IGF-1 and its analogues.
What is the dose of IGF-1 LR3?
We do not publish dosages. This is not an oversight. No single figure works for everyone: the regimen depends on a person's medical history, on whatever medication they already take, and on the goal they are chasing, which is something a professional weighs with the case in front of them. What you can build is the ability to walk into that appointment knowing what to ask.
Where can I learn to evaluate this properly?
This page tells you what IGF-1 LR3 is and what the evidence says. The PeptiXtreme course teaches the other half: what you would measure before considering anything, what you would watch, the specific questions you would take to a professional and when you would stop.