For a long time the honest answer to "which weight loss injection works better" was that nobody had properly tested them against each other. That changed with SURMOUNT-5, published in the New England Journal of Medicine, which put 751 adults with obesity on either tirzepatide or semaglutide for 72 weeks and measured what happened.
The headline is straightforward. The tirzepatide group lost an average of 20.2 percent of their body weight. The semaglutide group lost 13.7 percent. In kilograms that is roughly 22.8 against 15.0. Around 31 percent of people on tirzepatide lost at least a quarter of their starting body weight, against about 16 percent on semaglutide. Results vary from person to person and these are averages of a group, not a promise to an individual.
What interests us more is what the trial does not say. It compared the branded products at their maximum tolerated doses, so it tells you about the molecules rather than about any particular pharmacy's preparation. It reports averages, and averages hide the people at both ends: plenty of participants on semaglutide did very well. And it measured 72 weeks, which is long enough to be useful and short enough that it says nothing about year five.
It also does not tell you which one you should take. That still depends on what you have tried before, how you tolerated it, what your thyroid and pancreatic history looks like, and what you can comfortably afford to stay on for as long as you need it. A drug with a better average is not automatically the better choice for one particular person, which is the part a table can never decide.
If you want the practical version of this, we keep a side by side comparison of semaglutide and tirzepatide covering dosing, side effects and how our prescriber chooses between them.
