Medically reviewed by a licensed healthcare professional. Last updated March 2026.
Key Takeaways
- Tirzepatide (Zepbound) produced 20.2% average weight loss vs. 13.7% for semaglutide (Wegovy) in the SURMOUNT-5 head-to-head trial [1].
- Semaglutide has proven cardiovascular benefit from the SELECT trial; tirzepatide does not yet have this data [2].
- Both are weekly injections. Semaglutide also has an FDA-approved oral tablet option.
- Side effect profiles are similar, with tirzepatide showing slightly lower nausea rates in clinical trials [3][4].
- Cost is comparable: Wegovy at $499/mo (NovoCare) or $149-$299/mo (oral); Zepbound at $299-$449/mo (LillyDirect).
How They Work: The Key Difference
Both medications belong to the incretin-based therapy class, but they work through different mechanisms:
Semaglutide is a GLP-1 receptor agonist. It mimics one gut hormone (GLP-1) to reduce appetite, slow gastric emptying, and improve blood sugar regulation [5].
Tirzepatide is a dual GIP/GLP-1 receptor agonist. It mimics two gut hormones (GLP-1 and GIP) simultaneously, activating complementary metabolic pathways. The dual mechanism is believed to explain its greater average weight loss in clinical trials [3].
Think of it this way: semaglutide turns one dial to reduce appetite, while tirzepatide turns two related dials at once.
Clinical Trial Data: Head-to-Head
The most important data comes from the SURMOUNT-5 trial, the first direct comparison of these two medications for weight loss [1]:
| Outcome | Tirzepatide (15 mg) | Semaglutide (2.4 mg) |
|---|---|---|
| Average weight loss | 20.2% | 13.7% |
| Participants losing ≥10% | 82% | 67% |
| Participants losing ≥20% | 55% | 26% |
| Duration | 72 weeks | 72 weeks |
For a 220-pound person, this translates to:
- Tirzepatide: ~44 pounds lost on average
- Semaglutide: ~30 pounds lost on average
Both results are clinically significant. The 6.5 percentage point difference favoring tirzepatide is meaningful but should be weighed against other factors.
Individual Trial Results
Semaglutide (STEP 1 Trial) [4]:
- 14.9% average body weight loss at 68 weeks
- 86% of participants lost at least 5%
- 32% of participants lost at least 20%
Tirzepatide (SURMOUNT-1 Trial) [3]:
- 22.5% average body weight loss at 72 weeks (highest dose)
- 96% of participants lost at least 5%
- 63% of participants lost at least 20%
Cardiovascular Evidence
This is where semaglutide has a significant advantage.
The SELECT trial demonstrated that semaglutide 2.4 mg reduced major adverse cardiovascular events (heart attack, stroke, cardiovascular death) by 20% in adults with obesity and established cardiovascular disease [2]. This is the first GLP-1 medication to prove cardiovascular benefit specifically in patients with obesity (without requiring diabetes).
Tirzepatide does not yet have equivalent cardiovascular outcomes data. The SURPASS-CVOT trial is ongoing but results are not expected until late 2026 or 2027.
What this means for you: If you have established heart disease or are at high cardiovascular risk, the evidence supporting semaglutide is currently stronger. If cardiovascular risk is not a primary concern, this factor may be less decisive.
Side Effect Comparison
Both medications share similar gastrointestinal side effects, though rates differ:
| Side Effect | Semaglutide (STEP 1) | Tirzepatide (SURMOUNT-1) |
|---|---|---|
| Nausea | 44% | 33% |
| Diarrhea | 32% | 25% |
| Vomiting | 25% | 13% |
| Constipation | 23% | 17% |
| Discontinuation due to side effects | 7% | 6% |
Tirzepatide shows lower rates of nausea and vomiting in their respective trials, though cross-trial comparisons have limitations. The SURMOUNT-5 head-to-head trial confirmed generally comparable tolerability [1].
Both medications use gradual dose escalation to minimize side effects, and most GI symptoms improve within 4-8 weeks at each dose level.
Cost Comparison
| Factor | Semaglutide (Wegovy) | Tirzepatide (Zepbound) |
|---|---|---|
| List price | ~$1,349/mo | ~$1,059/mo |
| Self-pay program | $499/mo (NovoCare injection) | $299-$449/mo (LillyDirect) |
| Oral option | $149-$299/mo (oral Wegovy) | Not available |
| Commercial insurance | Varies by plan | Varies by plan |
| Medicare | Not covered for weight loss | Not covered for weight loss |
Cost advantage: LillyDirect's Zepbound pricing ($299-$449/mo) and oral Wegovy ($149-$299/mo) have made both medications significantly more accessible than their list prices suggest.
Available Formulations
Semaglutide:
- Weekly injection (Wegovy) — FDA-approved for weight loss
- Daily oral tablet (Wegovy) — FDA-approved December 2025
- Weekly injection (Ozempic) — FDA-approved for diabetes only
Tirzepatide:
- Weekly injection (Zepbound) — FDA-approved for weight loss
- Weekly injection (Mounjaro) — FDA-approved for diabetes only
- No oral formulation available
The oral option gives semaglutide an advantage for patients who prefer to avoid injections.
Decision Framework
Consider tirzepatide (Zepbound) if:
- Maximizing weight loss is your primary goal
- You don't have established cardiovascular disease
- You can access LillyDirect pricing or insurance coverage
- You're comfortable with weekly injections
- Previous semaglutide treatment was ineffective
Consider semaglutide (Wegovy) if:
- You have established cardiovascular disease or high CV risk
- You prefer an oral medication (no injections)
- NovoCare or oral Wegovy pricing fits your budget
- Your insurance covers Wegovy but not Zepbound
- You value the longer safety track record
When either could work:
- Both medications are accessible and affordable for you
- You don't have cardiovascular disease
- You're open to either injection or oral administration
- Start with whichever your insurance covers or is more affordable. Switch if ineffective after 3-6 months at target dose.
Discuss your specific situation with a qualified provider. Find GLP-1 clinics near you or compare telehealth providers that prescribe both medications.
Medical Disclaimer: This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Individual results vary. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you are experiencing a medical emergency, call 911.
Sources
- Aronne LJ, et al. "Tirzepatide vs Semaglutide for Weight Loss in Adults with Obesity (SURMOUNT-5)." ClinicalTrials.gov NCT05822609.
- Lincoff AM, et al. "Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT)." New England Journal of Medicine. 2023;389:2221-2232.
- Jastreboff AM, et al. "Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1)." New England Journal of Medicine. 2022;387:205-216.
- Wilding JPH, et al. "Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1)." New England Journal of Medicine. 2021;384:989-1002.
- FDA. Wegovy Prescribing Information. https://www.accessdata.fda.gov/drugsatfda_docs/label/2021/215256s000lbl.pdf