Glucagon is a 29-amino-acid peptide hormone secreted by the alpha-cells of the pancreatic islets. It is the principal counter-regulatory hormone to insulin: where insulin lowers blood glucose, glucagon raises it.
One gene, several hormones
Glucagon is not made from a dedicated gene. It is one of the peptides cut from proglucagon, the product of the GCG gene. The same precursor is processed differently depending on the tissue: in the pancreatic alpha-cell it yields glucagon, while in the gut and brain it yields GLP-1 and GLP-2. That shared origin is why glucagon, GLP-1 and GLP-2 are sometimes described together as the proglucagon family.
Mechanism
Glucagon acts at the glucagon receptor, a class B G-protein-coupled receptor. Its classical action is to raise hepatic glucose output, through glycogenolysis and gluconeogenesis, and it also slows gastrointestinal motility. That latter property underpins one of its licensed diagnostic uses.
UK licensing
Glucagon is unusual among the peptides discussed on this site in holding a UK marketing authorisation. Two preparations are licensed: glucagon hydrochloride as a powder for reconstitution (GlucaGen), given subcutaneously or intramuscularly, and a pre-filled glucagon auto-injector (Ogluo), given subcutaneously. Both are prescription-only medicines indicated for severe hypoglycaemia, and GlucaGen additionally carries a diagnostic indication to inhibit gastrointestinal motility during procedures. This is a licensed medicine with a defined clinical role; it is not a research reagent.
Research relevance
Glucagon is now studied less as a hormone in isolation than as one arm of multi-receptor metabolic drugs. Retatrutide, for example, is designed to activate the GIP, GLP-1 and glucagon receptors together, and the glucagon-receptor component is the arm associated with increased energy expenditure. Glucagon-receptor antagonists, conversely, have been investigated as glucose-lowering agents. Both directions remain active research questions, and neither is settled.
Evidence and uncertainty
For the licensed hypoglycaemia indication the evidence is long-established. For glucagon-receptor modulation as a weight-management strategy, the evidence is early and indirect: it comes from trials of multi-receptor agonists in which the glucagon arm cannot be isolated from the GIP and GLP-1 arms. That distinction is stated here rather than implied.
Legal position
Glucagon is regulated as a prescription-only medicine under the Medicines Act 1968 and the Human Medicines Regulations 2012. Unlicensed research peptides discussed elsewhere on this site are not medicines and remain research-use-only; nothing in this explainer changes that, and nothing here is medical advice.
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.