IGF-1 — insulin-like growth factor 1, also called somatomedin C — is a small, single-chain peptide hormone and the principal mediator of many of the growth-promoting actions of growth hormone. Growth hormone is released by the pituitary, and much of its effect on muscle, bone and connective tissue is exerted indirectly, through IGF-1 produced in the tissues. In acromegaly — the classic condition of growth-hormone excess — circulating IGF-1 rises in step with growth hormone, and IGF-1 is the measurement used to follow the disease.

That biology has produced two very different commercial objects. At one end is a recombinant human IGF-1 that holds a marketing authorisation as a medicine. At the other is a modified, long-acting analogue sold as a research reagent, with no licence and no controlled human trial record. The distance between them is the subject of this explainer.

The licensed end: mecasermin

Mecasermin is recombinant human IGF-1. Marketed as Increlex, it received a marketing authorisation valid throughout the European Union on 3 August 2007, assessed by the European Medicines Agency for the treatment of severe primary IGF-1 deficiency (growth failure); the European public assessment report sets out that assessment.

Two cautions follow for UK readers. First, an EU authorisation granted in 2007 is not itself a UK marketing authorisation: since the end of the transition period the UK keeps its own licensing register, and a product's UK status must be read from the MHRA rather than assumed from the EU record. Second, mecasermin is a prescription medicine for a diagnosed endocrine deficiency. It is not a general "growth" product, and it has no consumer or self-selected route.

The research analogue: IGF-1 LR3

The compound encountered in the research-peptide market is different. "LR3" denotes a long analogue of IGF-1 carrying an N-terminal extension and an arginine substitution at position 3 (replacing the native glutamic acid). The design is deliberate: those changes reduce the analogue's affinity for the IGF-binding proteins that normally sequester native IGF-1, which extends its effective half-life and increases its potency in cell and animal models relative to the unmodified hormone.

That is a laboratory property, not a clinical one. IGF-1 LR3 does not hold a UK marketing authorisation, is not a licensed medicine in any jurisdiction surveyed here, and is supplied to laboratories as a research reagent. The human clinical literature under the analogue's own terms is effectively absent: a PubMed search for "long Arg3 IGF-1 LR3" returns a handful of results, and a narrower search returns two, neither a controlled human study of the analogue. The research is preclinical, and that is stated here rather than implied.

MGF: the splice variant next door

A related entity in the same literature is mechano growth factor (MGF, also written IGF-1Ec), a splice variant of IGF-1 expressed in skeletal muscle in response to mechanical loading. MGF has been studied chiefly in rodent and cell models, where it is reported to act locally on muscle. The indexed literature is small: a PubMed search for "mechano growth factor IGF-1Ec skeletal muscle" returns two results. As with the LR3 analogue, the biology is preclinical, and no controlled human trial record establishes an effect in people.

The UK regulatory position

Under the Human Medicines Regulations 2012 (SI 2012/1916), a substance presented as having a medicinal purpose — treating, preventing or modifying a physiological function in a human being — is a medicine, and supplying it for that purpose requires a marketing authorisation. The MHRA licenses medicines in the UK and enforces that framework.

A "research use only" label does not, by itself, settle the question. The MHRA's stated position is that classification turns on how a product is presented and intended in practice, case by case: where material is promoted for human use, or sold in a way that makes human use its evident purpose, the research designation does not insulate the supply. The regulator has applied that test to clinics promoting peptide injections and has investigated online peptide sellers on the same basis. For a compound such as IGF-1 LR3 — unlicensed, with no human trial record — the label describes a genuine laboratory use; it is not a licence, and it does not make the material suitable for administration to people.

What the evidence does and does not show

  • IGF-1 is an endogenous peptide hormone and a core part of the growth-hormone axis; its physiology is not in dispute.
  • A recombinant human IGF-1 (mecasermin) is an authorised medicine in the EU for a specific, rare endocrine indication.
  • The long-acting analogue sold as IGF-1 LR3 is a research reagent. Its distinguishing pharmacology — reduced IGF-binding-protein binding and an extended half-life — is established in preclinical work, not in human trials.
  • MGF is a muscle-expressed IGF-1 splice variant studied preclinically. No controlled human trial record supports a conclusion about effects in people.
  • Nothing here is a recommendation, a protocol, or a statement that any of these compounds treats, cures or prevents a condition.

Research use only

This article describes published research and the UK regulatory position. Peptide Data does not sell compounds and does not provide consumption, dosing or administration guidance for any substance. Material sold for laboratory research is not for human use.

This article is AI-researched and editorially reviewed. It is provided for research and educational purposes only and is not medical advice. Research peptides are not licensed for human consumption in the UK.