The growth-hormone secretagogues are a family of peptides that act upstream of growth-hormone (GH) release. They are usually discussed as a single class. Pharmacologically they are not: three distinct routes converge on the same pituitary output, and the members differ in receptor, half-life and evidence base.

Peptide Data grades every compound against one four-tier scale — Strong, Moderate, Limited, Anecdotal. This explainer sets out what the class contains, what the human literature actually measures, and where the members sit under UK law. No member of this class is authorised as a medicine in the UK, and nothing here is a protocol or a guide to administration.

Three routes to GH release

GHRH-receptor agonists. Growth-hormone-releasing hormone (GHRH) is a hypothalamic peptide that binds the pituitary GHRH receptor and stimulates GH release. The class's synthetic members are modelled on it: somatorelin (GHRH 1-44), sermorelin (the 1-29 fragment), tesamorelin (a stabilised analogue) and the modified GRF peptides such as CJC-1295. The engineering is directed at half-life, because native GHRH is cleared within minutes.

Ghrelin-receptor agonists (GHS-R1a). Ghrelin is the endogenous ligand for the growth-hormone secretagogue receptor, cloned in 1996 as a receptor that released GH from pituitary cells; ghrelin itself was described in 1999 (Howard et al., 1996; Kojima et al., 1999). The synthetic growth-hormone-releasing peptides — GHRP-6, GHRP-2, ipamorelin and hexarelin — were developed largely before ghrelin was known and act at the same receptor. This route is distinct from the GHRH receptor.

Combination approaches. Some research has paired a GHRH-receptor agonist with a ghrelin-receptor agonist on the basis that the two act at different receptors. That is a mechanistic observation from small studies of GH release, not evidence of clinical benefit.

What the literature measures

Most of the human literature in this class measures a surrogate — a rise in serum GH after a single dose — rather than a clinical endpoint. That distinction is usually lost when the class is discussed as one thing.

  • Sermorelin was once authorised in some jurisdictions as a diagnostic and paediatric GH-deficiency agent, and was later withdrawn. It is not authorised in the UK.
  • Tesamorelin has the largest clinical programme in the class, studied in HIV-associated visceral adiposity, with an approved product in the United States and no UK marketing authorisation.
  • GHRP-6, GHRP-2, ipamorelin and hexarelin have small acute-release studies in healthy volunteers but no controlled efficacy programme of the kind a licensing decision would rest on.
  • CJC-1295 and related modified GRFs are research reagents; the peer-reviewed human record is thin.

The distinction matters for grading: a reproducible rise in a hormone is not the same as a demonstrated clinical outcome.

UK regulatory position

Under the Medicines Act 1968 and the Human Medicines Regulations 2012, whether a peptide is a medicine turns on how it is presented and how it is intended to be used, decided by the MHRA case by case. A product marketed with a claim to modify a bodily function is likely to be a medicine requiring a marketing authorisation, and the MHRA has said it disregards 'research purposes' labelling where that label is being used to avoid medicines regulation.

On the evidence available to this reference, no GHRH-receptor agonist or ghrelin-receptor agonist holds a UK marketing authorisation. Members of the class circulate as research reagents and, in some cases, as unlicensed products. That is the same footing as most of the research-peptide field, and the same compliance position applies: research use only.

Evidence grades

The class sits at Limited as a whole. That grade reflects the absence of large controlled human trials measuring clinical outcomes for most members, not an absence of biological activity — the acute GH-release pharmacology is well described. Tesamorelin is the member with the strongest human dataset, and even there the evidence is indication-specific.

Summary

One pituitary output, three pharmacological routes. The class is characterised by a deep and reproducible acute pharmacology alongside a thin clinical record, no UK-licensed member, and a regulatory position that turns on presentation and intended use. The research is stated here as research; nothing in this article is advice on 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.