SURPASS-2: tirzepatide vs semaglutide head-to-head
SURPASS-2 is the only large randomized trial that put tirzepatide directly against semaglutide in type-2 diabetes patients. 1,879 adults, 40 weeks, four arms: tirzepatide 5 mg, 10 mg, 15 mg, vs semaglutide 1.0 mg. The results moved the diabetes treatment guidelines.
The trial design
| Property | SURPASS-2 |
|---|---|
| Population | 1,879 adults with type-2 diabetes inadequately controlled on metformin |
| Baseline HbA1c | ~8.3% (mean) |
| Baseline weight | ~93.7 kg (mean) |
| Duration | 40 weeks of treatment |
| Arms | Tirzepatide 5 mg / 10 mg / 15 mg weekly; semaglutide 1.0 mg weekly |
| Primary endpoint | Non-inferiority of tirzepatide vs semaglutide on HbA1c |
HbA1c results
| Arm | HbA1c reduction at 40 weeks | Patients reaching <7.0% | Patients reaching <5.7% (non-diabetic range) |
|---|---|---|---|
| Semaglutide 1.0 mg | −1.86% | ~79% | ~19% |
| Tirzepatide 5 mg | −2.01% | ~85% | ~27% |
| Tirzepatide 10 mg | −2.24% | ~89% | ~40% |
| Tirzepatide 15 mg | −2.30% | ~92% | ~46% |
The "<5.7%" row is striking: nearly half of tirzepatide 15 mg patients had HbA1c levels that, in a different context, would be called non-diabetic. Semaglutide 1.0 mg achieved this in about a fifth.
Weight loss results
| Arm | Weight change at 40 weeks | % of body weight |
|---|---|---|
| Semaglutide 1.0 mg | −6.2 kg | ~6.6% |
| Tirzepatide 5 mg | −7.6 kg | ~8.1% |
| Tirzepatide 10 mg | −9.3 kg | ~9.9% |
| Tirzepatide 15 mg | −12.4 kg | ~13.2% |
At top dose, tirzepatide produced roughly twice the weight loss of standard-dose semaglutide. The weight-loss gap is wider than the HbA1c gap, which is consistent with GIP's independent contribution to body-composition outcomes.
Side-effect rates
The GI side effect profile was remarkably similar across all arms:
| Side effect | Semaglutide 1.0 mg | Tirzepatide 15 mg |
|---|---|---|
| Nausea | ~18% | ~22% |
| Vomiting | ~8% | ~10% |
| Diarrhea | ~12% | ~16% |
| Treatment discontinuation due to AE | ~5% | ~6% |
The bigger drug didn't produce proportionally bigger side-effect rates. This is partly a credit to GIP's anti-nausea effect (see GIP receptor explained) and partly a titration discipline observed in trial.
What the trial doesn't answer
- Semaglutide 2.4 mg vs tirzepatide 15 mg. SURPASS-2 used semaglutide at its T2D dose, not the higher weight-loss dose. The gap at maximum-dose comparison is smaller — see SURMOUNT-1 vs STEP-1 (~21% vs ~15% weight loss).
- Long-term retention. 40 weeks is enough to show short-term effect. Real-world retention at 2–3 years differs substantially.
- Non-T2D obesity populations. SURPASS-2 was T2D patients. SURMOUNT-1 is the comparable trial in non-diabetic obesity.
- Cardiovascular outcomes. SELECT (semaglutide) demonstrated MACE reduction. SURMOUNT-MMO (tirzepatide) is the corresponding trial; results expected 2026–2027.
Clinical takeaways
For T2D management in patients tolerating GLP-1 therapy:
- Tirzepatide is the better choice for HbA1c reduction and for weight loss.
- The gap at top dose is meaningful (~0.4 percentage points HbA1c, ~6 kg weight) but not dramatic at lower doses.
- Side-effect profiles are similar enough that drug choice can be driven by efficacy without major tolerability trade-off.
- Cost, availability, and prior-tolerance experience often decide between them in real practice.
FAQ
Why is SURPASS-2's semaglutide arm only 1.0 mg, not 2.4 mg?
SURPASS-2 was a T2D trial; 1.0 mg is semaglutide's top labeled T2D dose. 2.4 mg is the Wegovy dose, used for weight-loss indications. The trial design used both drugs at their then-standard T2D doses for fair comparison.
Is SURPASS-2 the only head-to-head?
Currently yes for a fully-powered randomized trial. Retrospective comparisons (real-world data, indirect comparisons) exist but are inferior evidence.
How long until SURPASS-2 results expired or were updated?
They haven't. The trial completed in 2021 and the data is still the reference. Real-world follow-ups (e.g., SURMOUNT-MMO) extend the picture into cardiovascular outcomes, but the head-to-head efficacy numbers remain.
Do the results extrapolate to non-diabetic users?
Mostly. The weight-loss gap is reproduced in obesity-only trials (SURMOUNT-1 vs STEP-1). The HbA1c gap is less relevant in non-diabetic users — both drugs do plenty.
Related reading
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