No — GLP-1 is a hormone the body produces naturally. It is released by L-cells in the intestine after you eat. The drugs you may have heard of (semaglutide, tirzepatide, liraglutide, retatrutide) are man-made molecules that copy GLP-1's structure and effects, with chemical modifications that make them last days rather than minutes.

Three main things. First, it tells the pancreas to release insulin in response to rising blood sugar — but only when sugar is elevated, which is why GLP-1 drugs do not cause low blood sugar on their own. Second, it slows the rate at which the stomach empties food into the gut, so you feel full longer. Third, it acts on appetite centres in the brain to reduce hunger and food-reward signalling.

Why are GLP-1 drugs so effective?

Natural GLP-1 has a half-life of about 90 seconds because an enzyme called DPP-4 breaks it down almost instantly. Modern GLP-1 medicines are modified to resist DPP-4 and to bind to plasma albumin, extending their half-life from seconds to about a week. That allows continuous receptor signalling rather than a brief burst — and continuous signalling is what drives the appetite reduction and metabolic benefits observed in clinical trials.

Does GLP-1 only act on the gut and pancreas?

No. GLP-1 receptors are also expressed in the heart, brain, kidneys and several other tissues. Some of the cardiovascular benefits of GLP-1 medicines (such as the 20% reduction in major cardiac events seen with semaglutide in the SELECT trial) are now thought to be direct rather than simply consequences of weight loss.

What is GLP-1? Plain-English UK Explainer (2026)

One paragraph

GLP-1 stands for glucagon-like peptide-1. It is a small hormone produced by cells in the lining of the small intestine, released into the bloodstream when you eat. Its job is to coordinate the body's response to a meal — stimulating insulin release, slowing digestion, and signalling fullness. Modern weight-loss and diabetes medicines (Ozempic, Wegovy, Mounjaro, Saxenda, Rybelsus) are synthetic copies of GLP-1 engineered to stay in the body for days rather than minutes.

Where it comes from

GLP-1 is secreted by enteroendocrine L-cells, which sit in the lining of the ileum and colon. When food (especially fats and carbohydrates) reaches the intestine, L-cells release GLP-1 into the bloodstream within minutes. From there it acts on multiple tissues — pancreas, stomach, brain, heart — through a specific cell-surface receptor called the GLP-1 receptor.

Why natural GLP-1 wears off so quickly

Almost as soon as GLP-1 enters the bloodstream, an enzyme called DPP-4 (dipeptidyl peptidase-4) clips two amino acids off its end, inactivating it. The half-life of native GLP-1 is roughly 90 seconds. That is why a natural burst of GLP-1 after a meal lasts a few minutes at most — useful for coordinating a single meal, but not durable enough to drive sustained appetite reduction.

How medicines fix that

Synthetic GLP-1 agonists are modified to resist DPP-4 and to bind to albumin in the blood, which dramatically slows their clearance. Liraglutide's C-16 fatty-acid modification gives a 13-hour half-life. Semaglutide's C-18 fatty-diacid plus a spacer pushes it to about 7 days. Tirzepatide and retatrutide use similar chemistry. The result is that a single weekly injection (or daily, for liraglutide) keeps the receptor activated continuously instead of in seconds-long bursts.

The drug class this hormone created

The GLP-1 receptor agonist class now includes monoagonists (semaglutide, liraglutide), dual GLP-1/GIP agonists (tirzepatide), and the new triple GLP-1/GIP/glucagon agonists (retatrutide). For more on the mechanism, see our GLP-1 mechanism guide.

FAQs

Is GLP-1 a drug?: No — GLP-1 is a hormone the body produces naturally. It is released by L-cells in the intestine after you eat. The drugs you may have heard of (semaglutide, tirzepatide, liraglutide, retatrutide) are man-made molecules that copy GLP-1's structure and effects, with chemical modifications that make them last days rather than minutes.
What does GLP-1 do?: Three main things. First, it tells the pancreas to release insulin in response to rising blood sugar — but only when sugar is elevated, which is why GLP-1 drugs do not cause low blood sugar on their own. Second, it slows the rate at which the stomach empties food into the gut, so you feel full longer. Third, it acts on appetite centres in the brain to reduce hunger and food-reward signalling.
Why are GLP-1 drugs so effective?: Natural GLP-1 has a half-life of about 90 seconds because an enzyme called DPP-4 breaks it down almost instantly. Modern GLP-1 medicines are modified to resist DPP-4 and to bind to plasma albumin, extending their half-life from seconds to about a week. That allows continuous receptor signalling rather than a brief burst — and continuous signalling is what drives the appetite reduction and metabolic benefits observed in clinical trials.
Does GLP-1 only act on the gut and pancreas?: No. GLP-1 receptors are also expressed in the heart, brain, kidneys and several other tissues. Some of the cardiovascular benefits of GLP-1 medicines (such as the 20% reduction in major cardiac events seen with semaglutide in the SELECT trial) are now thought to be direct rather than simply consequences of weight loss.