GLP-1 & incretin drugs: the overview

They mimic gut incretin hormones. Semaglutide (Wegovy for weight, Ozempic for diabetes) is a GLP-1 receptor agonist; tirzepatide (Zepbound / Mounjaro) is a dual GIP + GLP-1 agonist. Both act on appetite centres in the hypothalamus and hindbrain to cut hunger and food intake, slow gastric emptying, and boost glucose-dependent insulin release. The appetite effect is the main driver of weight loss. Both are once-weekly injections; liraglutide (Saxenda) is an older, once-daily GLP-1.

Over ~68–72 weeks, mean weight loss runs about 15% for semaglutide 2.4 mg (STEP 1), up to ~21% for tirzepatide 15 mg (SURMOUNT-1), and ~8% for liraglutide. Head-to-head, tirzepatide beat semaglutide (−20.2% vs −13.7%, SURMOUNT-5). About half of people on the top tirzepatide dose lose ≥20% — results previously seen only with surgery. Evidence ●●●●●

Semaglutide cut major cardiovascular events by 20% in a 17,600-person trial of people with heart disease and obesity (SELECT), and tirzepatide is now approved for moderate-to-severe obstructive sleep apnoea. The benefits extend past the scale.

Approved for adults with BMI ≥30, or ≥27 with a weight-related condition (e.g. hypertension, type 2 diabetes, dyslipidaemia), plus diet and activity — and for adolescents 12+ with obesity. Semaglutide also carries a cardiovascular-risk-reduction indication, tirzepatide a sleep-apnoea one. These are the same BMI thresholds as older anti-obesity drugs.