Semaglutide vs Tirzepatide:
The Definitive Comparison
SURMOUNT-5 (NEJM 2025) settled the debate: Tirzepatide delivered 47% greater weight loss than Semaglutide head-to-head. Here's the full data from both trial programs.
SURMOUNT-5: The Verdict (NEJM 2025)
751 participants · 72 weeks · Maximum tolerated doses · 1:1 randomized
-20.2%
Tirzepatide
10–15mg
-13.7%
Semaglutide
1.7–2.4mg
47%
Greater Weight Loss
Tirzepatide advantage
50.3 lbs
Tirzepatide Avg Loss
vs 33.1 lbs sema
Mechanism Comparison
Semaglutide (Wegovy / Ozempic)
GLP-1 Receptor Only
- 94% structural homology to human GLP-1
- Half-life ~7 days (165 hours)
- 89% subcutaneous bioavailability
- Available in oral form (Rybelsus)
- SELECT trial: 20% MACE reduction (n=17,604)
Tirzepatide (Zepbound / Mounjaro)
Dual GIP + GLP-1 Receptor
- GIP receptor affinity equals native GIP
- Half-life ~5 days (120 hours)
- Synergistic GIP + GLP-1 co-activation
- 47% greater weight loss vs semaglutide (SURMOUNT-5)
- Lower GI discontinuation: 2.7% vs 5.6%
STEP Trial Program
| Trial | n | Duration | Weight Loss |
|---|---|---|---|
| STEP 1 | 1,961 | 68 wks | -14.9% |
| STEP 2 (T2D) | 1,210 | 68 wks | -9.6% |
| STEP 3 (+ behavioral) | 611 | 68 wks | -16.0% |
| STEP 5 (2 year) | 304 | 104 wks | -15.2% |
Consider Retatrutide — -28.7% Weight Loss
The triple-agonist outperforms both. Retatrutide adds glucagon receptor activation on top of GLP-1 + GIP.
SURMOUNT Trial Program
| Trial | n | Duration | Best Result |
|---|---|---|---|
| SURMOUNT-1 | 2,539 | 72 wks | -22.5% (15mg) |
| SURMOUNT-2 (T2D) | 938 | 72 wks | -15.7% (15mg) |
| SURMOUNT-4 (withdrawal) | 670 | 88 wks | +14% regain off drug |
| SURMOUNT-5 (vs sema) | 751 | 72 wks | -20.2% vs -13.7% |
SURMOUNT-1 highlight: at 15mg, 39.7% of participants lost ≥25% body weight — a threshold previously only achievable through bariatric surgery.
Cardiovascular Outcomes
Semaglutide — SELECT Trial
17,604 participants across 41 countries
Obese adults with established CVD, without diabetes
Result: 20% reduction in MACE (HR 0.80, p<0.001)
First GLP-1 CV benefit demonstrated in a non-diabetic obese population
Tirzepatide — CV Data
No dedicated MACE-endpoint trial completed as of March 2026
SURMOUNT trials show favorable: ↓BP, ↓lipids, ↓hsCRP
SURPASS-2: superior A1C reduction vs semaglutide 1mg in T2D
For CV endpoint research: semaglutide has stronger evidence base
Which Should You Research?
Choose Semaglutide when:
- Studying pure GLP-1 receptor pharmacology
- Cardiovascular endpoint research (SELECT trial data)
- Oral formulation studies (Rybelsus)
- Long-duration efficacy (104-week STEP 5 data)
- Lower dose protocols / budget constraints
Choose Tirzepatide when:
- Maximizing weight loss magnitude (-22.5% vs -14.9%)
- Dual GIP/GLP-1 co-agonism research
- Tolerability-focused research (2.7% vs 5.6% discontinuation)
- Glycemic control studies (superior HbA1c vs sema 1mg)
- Higher-dose protocols ($3.83/mg vs $9.33/mg at best price)
Research Pricing at Apollo
Frequently Asked Questions
Is tirzepatide more effective than semaglutide?
Yes, based on SURMOUNT-5 (NEJM 2025, n=751, 72 weeks). Tirzepatide produced 47% greater weight loss (-20.2% vs -13.7%). Tirzepatide's GIP + GLP-1 dual agonism produces synergistic metabolic effects exceeding selective GLP-1 agonism.
Does semaglutide have cardiovascular benefits tirzepatide lacks?
Yes. SELECT trial (n=17,604, 41 countries) showed 20% MACE reduction with semaglutide in obese adults without diabetes (HR 0.80, p<0.001). No equivalent tirzepatide CVOT has been completed as of March 2026.
Which has fewer side effects?
In SURMOUNT-5 head-to-head: tirzepatide had 2.7% GI-related discontinuation vs semaglutide's 5.6%. Despite greater efficacy, tirzepatide was better tolerated — possibly because GIP receptor activation modulates GI signaling differently.
What happens when you stop taking them?
Both show significant regain. STEP 4: +6.9% regain (vs -7.9% additional loss for continuers). SURMOUNT-4: +14.0% regain (vs -5.5% additional for continuers). Only 16.6% who stopped tirzepatide maintained ≥80% of lost weight vs 89.5% who continued.
What about retatrutide — is it better than both?
Yes in terms of weight loss. Retatrutide (triple GLP-1/GIP/Glucagon agonist) delivered -28.7% in TRIUMPH-4 Phase 3, vs -22.5% tirzepatide and -14.9% semaglutide. However, it has higher GI side effects (18.2% discontinuation) and is not yet FDA-approved.
Shop Both at Apollo Peptide Sciences
Research-grade Semaglutide and Tirzepatide — >98% purity, COA documentation.