Glucagon-like peptide-1 (native)
GLP-1, GLP-1 (7-36) amide, GLP-1 (7-37), native GLP-1, incretin
GLP-1 is the gut hormone behind the current generation of diabetes and obesity medicines. It is released from intestinal L-cells after eating and amplifies insulin secretion in a glucose-dependent way, suppresses glucagon, slows gastric emptying and reduces appetite through the brainstem and hypothalamus. The native peptide itself survives only a couple of minutes in blood, which is why every GLP-1 medicine is a modified analogue rather than the hormone itself.
Mechanism
GLP-1 is produced when prohormone convertase 1/3 processes proglucagon in intestinal L-cells, the same precursor that yields glucagon in pancreatic alpha cells under different processing, and GLP-2, oxyntomodulin and glicentin in the gut. The principal circulating bioactive forms are GLP-1(7-36) amide, which predominates in humans, and GLP-1(7-37). Secretion is biphasic: an early rise within 15 minutes, too fast to be explained by nutrients reaching the distal L-cell mass and therefore attributed to neural and hormonal signals from the proximal gut, followed by a sustained phase as nutrients arrive in the ileum and colon.
GLP-1 acts at the GLP-1 receptor, a class B G-protein-coupled receptor coupled to Gs. On beta cells, receptor activation raises cyclic AMP, activates protein kinase A and Epac2, and amplifies glucose-stimulated insulin secretion. The amplification is strictly glucose-dependent (below roughly 4 mmol/L the effect falls away), which is why GLP-1 receptor agonism does not by itself cause hypoglycaemia, a decisive advantage over sulfonylureas and insulin. GLP-1 also suppresses glucagon release from alpha cells, again glucose-dependently, and this contributes as much to glucose lowering as the insulin effect does.
Beyond the islet, GLP-1 slows gastric emptying via vagal pathways, which blunts postprandial glucose excursions and contributes to satiety, and acts on GLP-1 receptors in the hypothalamic arcuate nucleus, area postrema and nucleus tractus solitarius to reduce food intake. The area postrema sits outside the blood-brain barrier, which is why circulating GLP-1 can act centrally, and also why nausea is the characteristic dose-limiting effect of the whole class. Native GLP-1 is cleaved at the Ala8-Glu9 bond by dipeptidyl peptidase-4 to the largely inactive GLP-1(9-36) amide, and is further cleared by neutral endopeptidase and the kidney. This degradation begins within the capillary bed of the gut itself, so only a minority of secreted GLP-1 reaches the systemic circulation intact.
What the research shows
Kreymann and colleagues established GLP-1(7-36) as a physiological incretin in man in the Lancet in 1987, showing that infusion at concentrations achieved after a meal augmented insulin secretion. Nauck and colleagues then produced the two results that defined the field's direction. In 1993 in Diabetologia they showed that a GLP-1(7-36) amide infusion normalised fasting plasma glucose within four hours in poorly controlled type 2 diabetic patients while placebo did not, a striking demonstration that the incretin defect was pharmacologically addressable. In the same year in the Journal of Clinical Investigation they showed that, unlike GIP, GLP-1's insulinotropic activity was largely preserved in type 2 diabetes, retaining about 71 per cent of the normal response against a 54 per cent deficit for GIP. That asymmetry is why every incretin drug programme for the following two decades was built on GLP-1.
The furthest anyone took the native peptide therapeutically was Zander and colleagues, who in the Lancet in 2002 gave 20 patients with type 2 diabetes six weeks of continuous subcutaneous GLP-1 or saline in a parallel-group pilot study, reporting improvements in glycaemic control, insulin sensitivity and beta-cell function. That study is the practical proof that sustained GLP-1 receptor activation works in humans, and equally the proof that it can only be delivered by continuous infusion or by engineering, since a 2-minute half-life admits no other route. Development moved wholly to DPP-4-resistant, albumin-binding or fatty-acylated analogues and to DPP-4 inhibitors that raise endogenous GLP-1. The honest framing for a general reader is that the celebrated trial evidence in this area (cardiovascular outcome trials, large weight-management programmes) belongs to those engineered molecules. Native GLP-1 is the physiological starting point and a research tool, not a therapy.
Evidence assessment
Limited evidence
This record covers the native hormone, not its engineered analogues. Human studies of native GLP-1 are short mechanistic infusion studies and one small 6-week continuous-infusion parallel-group study in 20 patients. There is no phase 3 evidence for native GLP-1 and there never will be, because a 2-minute half-life makes it undevelopable. The very strong phase 3 evidence in this therapeutic area belongs to modified analogues such as liraglutide, semaglutide and dulaglutide, which are separate molecules with separate records; it must not be transferred to the native peptide.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Glucagon-like peptide-1 7-36: a physiological incretin in man Preclinical only
Established GLP-1(7-36) as a physiological incretin in humans, showing insulinotropic activity at concentrations reached after a meal. The founding human paper for the field.
Normalization of fasting hyperglycaemia by exogenous glucagon-like peptide 1 (7-36 amide) in type 2 (non-insulin-dependent) diabetic patients Preclinical only
GLP-1(7-36) amide infusion normalised fasting plasma glucose within four hours, while placebo did not, the demonstration that the incretin axis could be exploited pharmacologically in established type 2 diabetes.
Preserved incretin activity of glucagon-like peptide 1 [7-36 amide] but not of synthetic human gastric inhibitory polypeptide in patients with type-2 diabetes mellitus Preclinical only
GLP-1 retained approximately 71 per cent of its normal insulinotropic effect in type 2 diabetes (a non-significant reduction), whereas GIP's maximum effect was 54 per cent lower. This preserved activity is the reason GLP-1 rather than GIP became the basis of the incretin drug class.
Effect of 6-week course of glucagon-like peptide 1 on glycaemic control, insulin sensitivity, and beta-cell function in type 2 diabetes: a parallel-group study Preclinical only
Six weeks of continuous subcutaneous GLP-1 infusion improved glycaemic control, insulin sensitivity and beta-cell function. The longest human exposure to the native peptide, and a pilot study in 20 people. It demonstrates the principle while illustrating why continuous infusion is the only way to deliver an unmodified 2-minute-half-life peptide.
Safety
Native GLP-1 given by short infusion in research settings is generally well tolerated, with nausea the commonest effect and the principal dose-limiting one, mediated in part through the area postrema. Because the insulinotropic and glucagonostatic actions are both glucose-dependent, native GLP-1 does not by itself cause hypoglycaemia, though risk rises when it is combined with sulfonylureas or insulin. Slowed gastric emptying can cause early satiety, bloating and, at higher exposures, vomiting. The longer-term class concerns familiar from the licensed analogues (pancreatitis, gallbladder disease, and the rodent C-cell tumour signal that drives the medullary thyroid carcinoma contraindication on several analogue labels) derive from sustained receptor activation and long-duration human trials; none of that safety dataset exists for the native peptide, which has never been given chronically outside a 6-week study in 20 people. GLP-1 sold as a research chemical has no pharmacopoeial identity, purity or sterility assurance, no licensed status, and a half-life of roughly two minutes that makes any consumer application pharmacologically pointless. It is emphatically not a substitute for a prescribed GLP-1 receptor agonist, and treating it as one reflects a misunderstanding of why those medicines are engineered the way they are.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | Native GLP-1 has no UK marketing authorisation and is not a licensed medicine. Material offered for sale to consumers is an unlicensed research chemical. Licensed GLP-1 receptor agonists in the UK are prescription-only medicines and are chemically distinct from the native hormone; a 2-minute half-life makes native GLP-1 useless by intermittent injection regardless of purity. |
| United States | Native GLP-1 is not an approved medicine in the United States and has no FDA-approved indication. It is available only as a research reagent. Modified GLP-1 receptor agonists are separately approved for type 2 diabetes and for weight management, but those are distinct engineered molecules with their own labelling. |
| WADA (sport) | Not listed on the WADA Prohibited List. GLP-1 receptor agonists are not prohibited in or out of competition under any current category, and there is no established performance-enhancing rationale, though athletes in weight-category sports should be aware that governing bodies may have their own rules on weight manipulation. |
Questions
No. Those medicines are engineered analogues, modified to resist DPP-4 cleavage and, in most cases, fatty-acylated or fused to bind albumin so they last hours to days. Native GLP-1 has a half-life of roughly two minutes. The large trial evidence in this field belongs to the engineered molecules; the native hormone has never had a phase 3 trial and never will.
Because both of its main glucose-lowering actions are glucose-dependent. It amplifies insulin secretion only when glucose is elevated, and the effect falls away below roughly 4 mmol/L; it suppresses glucagon in the same conditional way. That is a genuine pharmacological advantage over insulin and sulfonylureas, though hypoglycaemia risk returns when a GLP-1 receptor agonist is combined with those drugs.
Partly through slowed gastric emptying, and partly through direct action on GLP-1 receptors in the area postrema and nucleus tractus solitarius in the brainstem. The area postrema lies outside the blood-brain barrier, so circulating GLP-1 can reach it. Nausea is the characteristic dose-limiting effect across the entire class and is closely tied to how quickly exposure is escalated.
Nauck's 1993 comparison is the reason. In type 2 diabetes GIP's maximum insulinotropic effect was 54 per cent lower than in controls, while GLP-1 retained about 71 per cent of the normal response. That asymmetry directed essentially all incretin drug development toward GLP-1 for two decades. GIP receptor pharmacology only returned to prominence much later, with engineered dual agonists.