Medically reviewed by a licensed healthcare professional. Last updated March 2026.

How They Work: The Key Difference

Both medications belong to the incretin-based therapy class, but they work through different mechanisms:

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 [1][3].

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 [7].

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%

A1C Reduction in Type 2 Diabetes

An earlier head-to-head comparison, the SURPASS-2 trial, tested tirzepatide against semaglutide 1 mg in adults with type 2 diabetes. All three tirzepatide doses (5 mg, 10 mg, 15 mg) produced superior A1C reductions compared to semaglutide 1 mg, with the 15 mg tirzepatide arm achieving nearly twice the weight loss of the semaglutide arm at 40 weeks [6].

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.

If brand-name list prices are still out of reach, compounded versions of both molecules ship from dozens of telehealth platforms. For compounded semaglutide, Hims and Ro are the most familiar names. For compounded tirzepatide, Henry Meds, GobyMeds, and Strut Health consistently come in cheapest. Specialist-led programs from Eden, Embody, Yucca Health, Mochi Health, and Found pair either molecule with more clinician time. Marketplace options (Sesame, PlushCare, Lemonaid) let you pay per visit, and newer entrants including Willow, Form Health, TrimRx, and Fridays have expanded the compounded market. For a coached wrapper around the medication, Calibrate, Noom, and WeightWatchers offer medication-plus-behavior-change tracks.

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.

⚠️Important

Compounded GLP-1 medications are not FDA-approved. While legal during FDA-recognized drug shortages, they do not undergo the same rigorous testing as brand-name drugs. Always verify your provider uses a licensed 503A or 503B compounding pharmacy.

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.

Ready to start your weight loss journey? Find a GLP-1 clinic near you and connect with a qualified provider today.

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

  1. Aronne LJ, et al. "Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5)." New England Journal of Medicine. 2025. doi:10.1056/NEJMoa2416394. https://www.nejm.org/doi/full/10.1056/NEJMoa2416394
  2. Lincoff AM, et al. "Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT)." New England Journal of Medicine. 2023;389:2221-2232. doi:10.1056/NEJMoa2307563. https://www.nejm.org/doi/full/10.1056/NEJMoa2307563
  3. Jastreboff AM, et al. "Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1)." New England Journal of Medicine. 2022;387:205-216. doi:10.1056/NEJMoa2206038. https://www.nejm.org/doi/full/10.1056/NEJMoa2206038
  4. Wilding JPH, et al. "Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1)." New England Journal of Medicine. 2021;384:989-1002. doi:10.1056/NEJMoa2032183. https://www.nejm.org/doi/full/10.1056/NEJMoa2032183
  5. FDA. Wegovy (semaglutide) Prescribing Information. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215256s024lbl.pdf
  6. Frías JP, et al. "Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2)." New England Journal of Medicine. 2021;385:503-515. doi:10.1056/NEJMoa2107519. https://www.nejm.org/doi/full/10.1056/NEJMoa2107519
  7. FDA. Zepbound (tirzepatide) Prescribing Information. 2024. https://www.accessdata.fda.gov/drugsatfda_docs/label/2024/217806s003lbl.pdf