How does semaglutide work?

Semaglutide is a GLP-1 receptor agonist — a synthetic copy of the gut hormone GLP-1 (glucagon-like peptide-1) that your body releases naturally when you eat. By binding the same receptors, it does four things at once:

• Slows gastric emptying — food leaves your stomach more slowly, so you feel full longer on less food.
• Signals satiety — it acts on appetite centers in the brain to reduce hunger and cravings.
• Triggers glucose-dependent insulin — the pancreas releases insulin only when blood sugar is high, which lowers glucose with little hypoglycemia risk.
• Suppresses glucagon — the hormone that raises blood sugar is turned down.

Together, the appetite effects drive weight loss and the glucose effects control diabetes — which is why the same molecule is sold both as Wegovy (weight management) and Ozempic (type 2 diabetes). In the STEP 1 trial, Wegovy produced about 15% average total body-weight loss at 68 weeks.

Why one dose lasts a week

Natural GLP-1 is destroyed within minutes. Semaglutide is engineered to resist that enzyme and to bind albumin in the blood, stretching its half-life to about a week — so the injectable forms are dosed once weekly. A daily oral tablet (Rybelsus, and an oral Wegovy) uses a special absorption enhancer to survive the stomach.

Single vs dual mechanism

Semaglutide works one pathway (GLP-1). Tirzepatide works two (GLP-1 plus GIP), which is why it edges semaglutide in head-to-head data — 20.2% vs 13.7% in SURMOUNT-5. See the semaglutide overview for brands, cost, and the cheapest routes.