How GLP-1 works: the hormone, and the drugs that copy it

GLP-1 stands for glucagon-like peptide-1

GLP-1 is short for glucagon-like peptide-1. It is an incretin — a hormone released by cells in your intestine when food arrives — and it is part of how your body coordinates digestion, insulin, and fullness after a meal. The drug class named after it is called GLP-1 receptor agonists, because each medicine in it activates the same receptor the hormone does.

Which matters, because “how does GLP-1 work” is really two questions with two different answers, and most pages answer only one of them.

The hormone: minutes

Your own GLP-1 is released after eating, prompts insulin when blood sugar is high, and is then broken down within minutes by an enzyme called DPP-4. It is a short-lived meal signal. Working normally, and doing its job, it is gone almost immediately.

The medication: days

That short life is the problem these drugs exist to solve, and the FDA label says exactly how. Semaglutide is described as a GLP-1 analogue with 94% sequence homology to human GLP-1 — nearly the same molecule, binding the same receptor, which the label calls the target for native GLP-1.

The interesting part is what the remaining few percent buys. The label names two changes: the molecule is stabilised against degradation by DPP-4, and it binds to albumin in the blood, which slows how fast the kidneys clear it. Those two modifications are the whole difference between a signal that lasts minutes and one that lasts days — and they are why the long-acting injectables are taken once a week rather than after every meal.

Mechanism of action, section 12.1 of the semaglutide tablets prescribing information, label revised 1/2026.

What the drugs in this class are called

Every FDA-approved medicine in this class, with the molecule inside it. The brand name and the molecule are often used interchangeably in conversation, which is where most of the confusion about “different” GLP-1 drugs comes from — Ozempic and Wegovy are both semaglutide, and Mounjaro and Zepbound are both tirzepatide.

Injection is no longer the only option

The class has changed quickly. Alongside the weekly injections, there are now daily tablets:

• Rybelsus (oral semaglutide) for type 2 diabetes, and Wegovy tablets for weight management — both must be taken on an empty stomach in the morning with no more than about four ounces of water, waiting roughly 30 minutes before eating, drinking, or taking other medication. That routine is the price of getting a peptide absorbed through the gut.
• Foundayo (orforglipron), approved in April 2026, is chemically different — a small molecule rather than a peptide. That is why it can be taken at any time of day without food or water restrictions, which is a meaningful practical difference rather than a marketing one.

If you have been searching for a “GLP-1 pill,” these are the real, FDA-approved ones. They are not the same as the unregulated supplements and “GLP-1 support” products sold online, which are a different category entirely.

The four things GLP-1 medications do

1. 01

   They prompt insulin — but only when blood sugar is high

   GLP-1 tells the pancreas to release insulin in a glucose-dependent way: the effect switches on when blood sugar is elevated and eases off when it is not. This is why GLP-1 medications, used on their own, carry a relatively low risk of hypoglycaemia. That risk rises when they are combined with insulin or sulfonylureas, which is a conversation to have with your prescriber.

2. 02

   They reduce glucagon

   Glucagon is insulin’s counterpart — it tells the liver to release stored glucose. GLP-1 suppresses glucagon after meals, so the liver adds less sugar to your bloodstream at the moment food is already arriving.

3. 03

   They slow gastric emptying

   Food leaves the stomach more slowly. Two consequences follow. The helpful one: you feel full sooner and stay full longer, so you eat less without deliberately restricting. The unhelpful one: this is the direct cause of most GLP-1 side effects — nausea, early fullness, reflux, bloating, and constipation. Eating a large or fatty meal on a slowed stomach is what typically triggers the worst nausea.

4. 04

   They act on appetite centres in the brain

   GLP-1 receptors also sit in regions of the brain that regulate hunger and reward. Acting on them reduces appetite and, for many people, quiets the persistent, intrusive thoughts about food often described as “food noise.” This is a genuine pharmacological effect, not willpower — which is also why appetite frequently returns if the medication stops.

The same slowed stomach that makes food last longer is what causes the nausea. The benefit and the side effect are not separate stories — they are one mechanism seen from two sides.

Why tirzepatide is not quite the same

Semaglutide (Ozempic, Wegovy, Rybelsus) acts on the GLP-1 receptor. Tirzepatide (Mounjaro, Zepbound) is a dual agonist: it acts on the GLP-1 receptor and also on the GIP receptor, a second incretin pathway. Both are commonly grouped under the “GLP-1” label in everyday conversation, but they are not identical drugs, and their trial results and side-effect profiles differ.

Why the dose starts low and climbs slowly

Because the gastrointestinal effects are dose-related, these medications are started at a low dose and increased in steps over weeks or months. The starting dose is generally not intended to be an effective treatment dose — it exists to let your digestive system adjust. Moving up too quickly is a common reason people find the side effects intolerable and stop. See our dosing and titration guide.

What this means in practice

• Side effects are the mechanism, not a malfunction. Feeling full quickly is the drug working; it is also why smaller, lower-fat meals help so much.
• Effects build gradually. Appetite change is often noticeable early, but these drugs reach steady levels in the body over weeks.
• It treats an ongoing condition. The appetite effect depends on the drug being present. Stopping generally means appetite returns.

This page is general education, not medical advice. Talk to your own healthcare provider about your situation before starting, stopping, or changing any medication.