Retatrutide vs tirzepatide vs semaglutide: what's the difference?

These three drugs are best understood as successive generations, each adding a receptor.

Semaglutide (branded Ozempic for diabetes, Wegovy for obesity) is a single GLP-1 receptor agonist. It is the most established of the three, with the deepest cardiovascular outcome data, and produces roughly 15% average bodyweight loss in trials. Attia is the panel's clearest source on the pharmacology.

Tirzepatide (Mounjaro/Zepbound) is a dual agonist — it hits both GIP and GLP-1 receptors. Attia explains this added GIP activity makes it more potent for weight loss than semaglutide. Some clinicians note the GIP component also improves insulin sensitivity and glucose uptake in muscle, which is one argument against going very low-carb on it.

Retatrutide is the next step: a triple agonist adding a glucagon receptor (GLP-1 + GIP + glucagon), which raises metabolic rate via mitochondrial uncoupling on top of appetite suppression. At the American Diabetes Association's June 2026 meeting, its pivotal Phase 3 TRIUMPH-1 trial reported roughly 25% average bodyweight loss at the top dose over 80 weeks, climbing toward 30% by week 104, with over a quarter of participants losing 35% or more — approaching bariatric-surgery territory. Important caveat: retatrutide is still investigational and not FDA-approved, and Precis's expert panel has not yet covered it directly (only passing mentions of the "triple agonist" concept). It also carries its own emerging signals, including a resting-heart-rate increase. The throughline across all three: the more potent the drug, the faster and deeper the weight loss — and the harder you have to work to protect muscle with protein and resistance training.