SURMOUNT-5: What the Head-to-Head Trial Actually Showed
SURMOUNT-5 was the first direct trial comparing tirzepatide and semaglutide for weight loss. At 72 weeks, tirzepatide produced about 20.2% mean weight reduction versus about 13.7% for semaglutide — a meaningful gap, though individual results vary. At 72 weeks tirzepatide produced about 20.2% mean weight reduction versus roughly 13.7% for semaglutide, making it the more potent option on average, though individual response varies and the result applies to the approved products.
- SURMOUNT-5 directly compared tirzepatide (Zepbound) and semaglutide (Wegovy) head-to-head.
- At 72 weeks: ~20.2% mean weight reduction with tirzepatide vs ~13.7% with semaglutide.
- Tirzepatide's dual GIP/GLP-1 mechanism is the leading explanation for the larger effect.
- Trial averages do not predict any one person's result; tolerability and cost also matter.
What SURMOUNT-5 was
For years, comparisons between tirzepatide and semaglutide relied on cross-trial inference — comparing separate studies with different participants, which is statistically unreliable. SURMOUNT-5 changed that by randomizing participants directly to one drug or the other, the gold standard for a fair comparison.
The trial enrolled adults with obesity, or overweight with a weight-related complication, and titrated each drug to its maximum tolerated dose over the study period. Because both arms were run under the same protocol with the same population, the difference in outcomes can be attributed to the drugs themselves rather than to differences in study design.
The results at 72 weeks
At 72 weeks, tirzepatide produced roughly a 20.2 percent mean reduction in body weight, compared with roughly 13.7 percent for semaglutide. That gap of about six and a half percentage points is clinically meaningful: for a person weighing 100 kilograms, it is the difference between losing about 14 kilograms and about 20 kilograms on average.
It is important to read these as averages across a population, not guarantees. A substantial share of semaglutide users lost more than the tirzepatide average, and some tirzepatide users lost less than the semaglutide average. Response varies with adherence, dose tolerance, diet, activity, and individual biology. The trial tells you which drug tends to produce more weight loss, not what you personally will lose.
| Outcome | Tirzepatide | Semaglutide |
|---|---|---|
| Mean weight reduction | ~20.2% | ~13.7% |
| Receptor targets | GIP + GLP-1 | GLP-1 only |
| Brand studied | Zepbound | Wegovy |
| Applies to compounded? | No | No |
Why tirzepatide produced more
The leading explanation is mechanism. Semaglutide activates a single incretin receptor, GLP-1. Tirzepatide activates two: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). The dual action appears to produce greater appetite suppression and metabolic effect for many people, which is consistent with tirzepatide's larger average results across the SURMOUNT programme, not just SURMOUNT-5.
This does not make tirzepatide universally better. Side-effect profiles overlap heavily, some people tolerate one molecule better than the other, and tirzepatide costs more both as brand and compounded. The mechanism explains the efficacy edge; it does not settle the choice for an individual patient.
| Concept | What it means |
|---|---|
| Mean reduction | The average across all participants, not a guarantee |
| Individual variation | Many users fall well above or below the mean |
| Brand vs compounded | Trial evidence applies only to the FDA-approved product studied |
What it means for your decision
SURMOUNT-5 strengthens the case that tirzepatide is the more effective weight-loss molecule on average. But the decision between them is clinical and personal. If maximum average weight loss is the priority and cost and tolerability allow, tirzepatide has the stronger head-to-head evidence. If cost is the constraint, semaglutide is cheaper and still produced substantial, clinically significant loss.
Neither compounded version carries this trial evidence: SURMOUNT-5 studied the FDA-approved brand products, and results should not be assumed to transfer to compounded formulations. Discuss the trade-off with a prescriber who knows your history.
Frequently asked questions
Is tirzepatide better than semaglutide?
On average for weight loss, SURMOUNT-5 showed tirzepatide produced more (about 20.2% vs 13.7% at 72 weeks). But tolerability, cost, and individual response mean it is not automatically the right choice for everyone.
Does this apply to compounded versions?
No. SURMOUNT-5 studied brand Zepbound and Wegovy. Compounded formulations have no formulation-specific trial evidence, and results should not be assumed to transfer.
What was the mean weight loss difference?
Roughly 20.2% with tirzepatide versus 13.7% with semaglutide at 72 weeks — about a six-and-a-half percentage point gap on average.
Sources
- Clinical trials via NEJM (STEP, SELECT, SURMOUNT, SURPASS).
- SURMOUNT-5 head-to-head trial results, 2025.
- FDA — human drug compounding and GLP-1 status.