How do weight loss medications work?

Most modern weight loss medications belong to a class called GLP-1 receptor agonists. GLP-1 (glucagon-like peptide-1) is a hormone your body naturally releases after eating. It tells your brain you're full, slows down how quickly food leaves your stomach, and helps regulate blood sugar by improving insulin production.

Medications like Mounjaro, Wegovy, Ozempic, and Saxenda work by mimicking this hormone. They effectively trick your brain into thinking you've just eaten, which suppresses your appetite and makes it easier to eat less without constantly feeling hungry. Mounjaro goes a step further — it also mimics a second hormone called GIP, which is why it's called a "dual agonist" and tends to produce slightly more weight loss.

Not all weight loss medications work this way. Orlistat (sold as Alli or Xenical) blocks fat absorption in the gut — a completely different approach. And Mysimba acts on the brain's appetite and reward centres using two active ingredients that aren't related to gut hormones at all.

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Each page covers how it works, dosing, clinical trial results, side effects, and cost.