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Two things share the name. A GLP‑1 is a hormone your gut makes after you eat. A GLP‑1 “drug” is a lab-made copy of it, stronger and longer-lasting — the mechanism behind Ozempic, Wegovy, Zepbound and Mounjaro. Here is how both work, in plain language.
GLP-1 is one of the incretin hormones — gut hormones released within minutes of eating. Natural GLP-1 does four useful things: it prompts the pancreas to release insulin (only when blood sugar is high, which is why it rarely causes lows on its own), it tells the liver to stop dumping sugar (by suppressing glucagon), it slows gastric emptyingso food leaves the stomach more slowly, and it acts on the brain’s appetite centers to make you feel full sooner and hungry less often. The catch: your own GLP-1 breaks down in a couple of minutes, so on its own it is far too short-lived to change your weight.
A GLP-1 receptor agonistis a molecule engineered to bind that same receptor but resist breakdown, so a single weekly injection keeps the signal switched on for days. That is the whole trick: not a new mechanism, but your body’s own fullness-and-insulin system amplified and made continuous. Practically, that means you eat less without constant willpower — which is why the class drives weight loss — and your blood sugar is better controlled, which is why the same drugs treat type 2 diabetes.
In the pivotal trials, average total weight loss was about 15% on semaglutide (Wegovy, STEP 1) and up to about 21% on tirzepatide (Zepbound, SURMOUNT-1) — figures that used to require surgery. Individual results vary a lot; our weight-loss projector shows the range on your own weight, and how much you can lose in a month sets honest early expectations.
The two that dominate: semaglutide — sold as Ozempic (diabetes), Wegovy (weight loss), and Rybelsus (an oral pill) — and tirzepatide — Mounjaro (diabetes) and Zepbound (weight loss). Older members include liraglutide (Saxenda/Victoza), dulaglutide (Trulicity), and exenatide (Byetta). Newer ones: the oral pill Foundayo (orforglipron), and retatrutide, a triple agonist, in late trials. Compare the two leaders in Wegovy vs Zepbound.
One nuance worth knowing: tirzepatide is a dual agonist. It hits the GLP-1 receptor and a second incretin receptor called GIP. That extra target is the leading explanation for why it tends to produce more weight loss — and a better fat-to-muscle ratio— than semaglutide, which acts on GLP-1 alone. People still say “GLP-1” for both, which is fine shorthand, but the mechanisms are not identical.
Because the name sells, plenty of things borrow it. Berberine(“nature’s Ozempic”) does not activate the GLP-1 receptor — see berberine vs Ozempic. “GLP-1 patches” can’t work: the peptide is far too large to cross intact skin (why patches fail). Foodscan nudge your own GLP-1 slightly, but nowhere near a drug’s effect. And “research peptide” vials sold online are unregulated and not the same as an approved product (the grey market, explained). If it is not one of the prescription receptor agonists above, it is not doing what a GLP-1 medication does.
Ready to go deeper? See how semaglutide works, how tirzepatide works, or find the right one with our 30-second quiz.