Semaglutide activates the GLP-1 receptor. Tirzepatide activates both GLP-1 and GIP receptors. In a direct trial of weekly injections in adults with obesity and without diabetes, tirzepatide led to greater average weight loss. That’s a useful comparison, but it doesn’t decide which medicine suits an individual person.
The clearest way to understand the difference is to separate three questions: how they work, what researchers compared, and what matters in your own prescribed routine.
One receptor, or two
A receptor is a receiving point on a cell. When the right molecule binds to it, a response begins. GLP-1 is a hormone involved in blood sugar and appetite; our guide to GLP-1 explains that signal in more detail.
Semaglutide is a GLP-1 receptor agonist, meaning it activates that receptor. Tirzepatide is an agonist at both GLP-1 and GIP receptors. GIP stands for glucose-dependent insulinotropic polypeptide, another hormone involved in the body’s response to food.
The Wegovy label and Zepbound label describe these actions. Semaglutide is the active ingredient in Wegovy; tirzepatide is the active ingredient in Zepbound.
Think of the receptor names as an explanation of the medicines’ targets. Counting targets isn’t a way to calculate how much weight someone will lose. For that, researchers have to compare outcomes in people.
What the head-to-head trial found
The SURMOUNT-5 trial randomly assigned 751 adults with obesity, without type 2 diabetes, to weekly injections for 72 weeks. Participants received their maximum tolerated study dose: tirzepatide at 10 or 15 mg, or semaglutide at 1.7 or 2.4 mg.
Average weight reduction was 20.2% with tirzepatide and 13.7% with semaglutide. The difference was 6.5 percentage points. Those percentages refer to starting body weight, not a weekly rate of loss.
The study was open-label, so participants and investigators knew which medicine was used, and Eli Lilly, tirzepatide’s manufacturer, funded it. Digestive side effects were the most common adverse events in both groups; most were mild or moderate and occurred during dose increases.
What those numbers mean for a reader
This was a comparison of particular injection regimens over a particular period. It wasn’t a test of every semaglutide formulation or every possible dose, and it wasn’t a trial of switching after a plateau.
That distinction matters when you encounter a headline saying one medicine is “better.” Better for average weight reduction in this trial is a specific finding. It doesn’t mean every participant had that result, or that someone doing well on a prescription needs to change it.
The study also doesn’t provide a dose conversion. The milligram amounts describe different molecules; they aren’t points on a shared strength scale. A change of medicine needs its own prescribing plan.
Compare the routine as well as the result
NIDDK’s guide to weight-management medicines describes treatment choice as a decision that includes likely benefits, side effects, other medicines, medical and family history, and cost. The biggest number in a trial is only one part of that conversation.
Both medicines also have important safety restrictions. The U.S. labels for Wegovy and Zepbound say they must not be used by people with a personal or family history of medullary thyroid carcinoma, or with multiple endocrine neoplasia syndrome type 2. These are specific conditions to discuss with the prescriber, rather than assuming that similar-looking medicines are interchangeable.
If your prescription changes, PepNote’s dose history keeps each logged dose attached to its medicine, amount, and date. That makes it easier to see where the old routine ended and the new one began.
The most useful comparison combines the research with a clear question about your care: what outcome are you aiming for, how is the current plan going, and what would a change be intended to improve?