Semaglutide, explained
The GLP-1 drug behind Ozempic and Wegovy is the best-studied peptide in consumer circulation. How it works, what the trials showed, and what to settle before starting.
What it is and how it works
Semaglutide is a synthetic copy of GLP-1, a hormone your gut releases after a meal. Native GLP-1 lasts a couple of minutes in the bloodstream; semaglutide was engineered — a fatty-acid chain that binds albumin, plus a substitution that blocks the enzyme that would otherwise break it down — to last about a week. That change in half-life is what turned a physiological curiosity into a once-weekly injection.
It prompts insulin release when glucose is high, suppresses glucagon, slows how fast the stomach empties and acts on appetite circuits in the brain. The weight loss follows mostly from the last two: food stays put longer and hunger signalling is blunted, so people eat less without constant effort. Doses start at 0.25 mg and step up roughly every four weeks to 2.4 mg.
What the trials showed
Semaglutide was approved for type 2 diabetes in 2017 and for chronic weight management in 2021, on the back of two full phase 3 programmes with tens of thousands of participants. The headline figures, against roughly 2–3% weight loss on placebo:
Side effects, cost and what happens when you stop
The common effects are gastrointestinal — nausea, constipation, diarrhoea — and cluster around each dose increase, which is why the trials titrated slowly. Rarer risks include gallbladder problems and pancreatitis. The drug is not for anyone with a personal or family history of medullary thyroid cancer or MEN2, or who is pregnant.
Appetite returns within weeks of stopping, and follow-up work found most of the lost weight came back within a year. Clinicians therefore treat semaglutide as a long-term medication, which makes price, insurance coverage and a prescriber who will monitor you the practical questions to settle first. Compounded and grey-market versions have repeatedly been found to contain salt forms never studied in people, and self-reconstitution dosing errors have produced documented hospitalisations — so where the drug comes from matters as much as the dose.
Want the long version? Read the full semaglutide write-up, with sources.
Research use only. A reading aid for the published literature, not medical advice. Talk to a licensed prescriber before starting or stopping any medication.