Released by the gut, cleared in minutes
Glucagon-like peptide 1 is produced by cells in the intestinal wall and released when food arrives. It is an incretin: a gut hormone that signals to the pancreas that glucose is on its way, so insulin release can begin before blood sugar has fully risen.
Its working life is extremely short. The enzyme DPP-4 cleaves it within a couple of minutes, which is appropriate for a meal signal and hopeless for a therapeutic. Every compound in this class exists because of that clearance problem.
The receptor it acts on is not confined to the pancreas. It appears in the brain, in the gastrointestinal tract and elsewhere, and that distribution is why activating it does considerably more than adjust insulin.
One detail explains more than it seems to. The hormone and glucagon are cut from the same precursor protein, proglucagon, by different enzymes in different tissues: the pancreas releases glucagon from it and the intestinal cells release GLP-1. Two hormones with broadly opposing effects on blood glucose share a gene, which is part of why one engineered peptide can be made to reach both receptors. The receptor entry on UniProt lists where it is expressed, and that tissue list is the short version of everything the next section describes.
What receptor activation does
The same receptor, in four different places, doing four different things.
How the class has developed
The first generation solved the clearance problem, mostly by attaching fatty acid chains that bind the molecule to albumin and slow its removal. Liraglutide reached about half a day; semaglutide reached about a week.
The second generation added receptors. Tirzepatide combined GLP-1 with GIP, the other incretin, and outperformed GLP-1 alone in head-to-head trials. Retatrutide added glucagon on top of both, which brings energy expenditure into a picture that was previously about intake.
Each step has less published evidence behind it than the last. That is not a criticism, it is what newer means, but it is worth holding in mind when you see effect sizes from different generations quoted side by side.
The compound pages carry the detail generation by generation. The liraglutide page covers the daily first-generation compound, the tirzepatide page the dual agonist that brought GIP back into the picture, and the receptor agonist literature indexed on PubMed holds the trial reports themselves. Read the class in that order and each step makes sense as an answer to the limits of the one before.
- GLP-1 the hormone, GLP-1 the classThe same name covers a natural hormone and a family of engineered analogues. They are not interchangeable.
- GIP is a different hormoneThe other incretin, with its own receptor. Dual agonists engage both; it is not a stronger GLP-1.
- GLP-3 is not in this familyNo such receptor exists. It is a market label, generally applied to triple-agonist material.
- Half-life is not potencyA weekly compound is not stronger than a daily one. It is cleared more slowly, which is a different property.
This class in the catalogue
Analysed by HPLC and released only at 99% purity or above, with a certificate for each batch.
Follow the class
Where to go once the pathway makes sense.
About the pathway
Four questions that clear up most of the confusion here.