The two biggest names in GLP-1 weight loss therapy, compared head-to-head with clinical trial data from STEP and SURMOUNT programs.
| Feature | Semaglutide | Tirzepatide |
|---|---|---|
| Brand Names | Ozempic, Wegovy, Rybelsus | Mounjaro, Zepbound |
| Mechanism | GLP-1 receptor agonist | Dual GLP-1/GIP agonist |
| Max Weight Loss | ~16.9% (STEP 1) | ~22.5% (SURMOUNT-1) |
| A1C Reduction | ~1.5–1.8% | ~2.0–2.3% |
| Dosing | Weekly injection (0.25–2.4 mg) | Weekly injection (2.5–15 mg) |
| FDA Approved | ✅ (T2D 2017, Obesity 2021) | ✅ (T2D 2022, Obesity 2023) |
| Cost (Cash Pay) | $900–$1,600/mo | $1,000–$1,200/mo |
| Key Trial | STEP program | SURMOUNT program |
Semaglutide mimics the natural hormone GLP-1 (glucagon-like peptide-1), which is released after eating. It works through a single receptor to:
Tirzepatide targets two receptors: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). This dual mechanism provides:
Think of GLP-1 as the appetite brake and GIP as the metabolic accelerator. Semaglutide applies the brake. Tirzepatide applies the brake and hits the accelerator on fat metabolism simultaneously. This dual action likely explains why tirzepatide shows greater weight loss in clinical trials.
STEP 1 (semaglutide 2.4 mg, 68 weeks, n=1,961): Mean weight loss of 14.9% with 1/3 of participants losing ≥20% body weight.
SURMOUNT-1 (tirzepatide 15 mg, 72 weeks, n=2,539): Mean weight loss of 22.5% with over half of participants losing ≥20% body weight.
Direct comparison: While not head-to-head in the same trial, tirzepatide at maximum dose shows approximately 5–7 percentage points greater weight loss than semaglutide at maximum dose. The SURMOUNT-5 trial confirmed tirzepatide's superiority head-to-head.
For patients with type 2 diabetes:
In the SURPASS-2 trial, tirzepatide achieved A1C <5.7% (non-diabetic range) in up to 46% of participants, compared to about 19% on semaglutide 1 mg.
Both are administered as once-weekly subcutaneous injections with gradual dose escalation to minimize GI side effects.
Tirzepatide has a slightly longer titration to maximum dose (20 weeks vs 16 weeks), but many patients achieve significant results before reaching the highest dose.
Both medications share a similar side effect profile due to their shared GLP-1 activity. The most common adverse events are gastrointestinal:
| Side Effect | Semaglutide | Tirzepatide |
|---|---|---|
| Nausea | ~44% | ~26–33% |
| Diarrhea | ~30% | ~21–25% |
| Vomiting | ~24% | ~12–18% |
| Constipation | ~24% | ~17–20% |
| Injection Site Rx | ~3–5% | ~3–7% |
Both carry a boxed warning for thyroid C-cell tumors (observed in rodent studies). They are contraindicated in patients with a personal or family history of medullary thyroid carcinoma or MEN2. Rare cases of pancreatitis have been reported with both medications.
Pricing can vary significantly based on insurance coverage, manufacturer programs, and pharmacy.
| Category | Semaglutide | Tirzepatide |
|---|---|---|
| Brand Cash Pay | $900–$1,600/mo | $1,000–$1,200/mo |
| With Insurance | $0–$300/mo (varies) | $0–$300/mo (varies) |
| Manufacturer Program | Novo Nordisk savings card | Lilly savings card |
Note: Compounded semaglutide has been widely available through telehealth platforms at lower prices. The FDA's compounding policies continue to evolve — check current availability with your provider.
The STEP (Semaglutide Treatment Effect in People with obesity) program included multiple Phase 3 trials:
The SURMOUNT program studied tirzepatide for obesity:
Both are excellent, FDA-approved options. Tirzepatide's dual mechanism gives it an edge in raw efficacy, but semaglutide has a longer track record and more formulation options. The best choice depends on your insurance coverage, treatment goals, and how your body responds. Work with your healthcare provider to decide.
Clinical trials show tirzepatide produces greater average weight loss (up to 22.5% in SURMOUNT-1) compared to semaglutide (up to 16.9% in STEP 1). However, individual responses vary significantly, and both are effective FDA-approved options.
Semaglutide is a GLP-1 receptor agonist (single mechanism), while tirzepatide is a dual GLP-1/GIP receptor agonist. This dual action is believed to contribute to tirzepatide's greater efficacy for both weight loss and blood sugar control.
Without insurance, brand-name semaglutide (Wegovy/Ozempic) costs approximately $900–$1,600/month, while tirzepatide (Mounjaro/Zepbound) costs approximately $1,000–$1,200/month. Compounded versions, where available, may cost less.
Both share similar GI side effects (nausea, vomiting, diarrhea, constipation). Tirzepatide may have slightly lower nausea rates at comparable efficacy levels. Both carry rare risks of pancreatitis and thyroid C-cell tumors (boxed warning).
Yes, switching is possible and sometimes recommended when patients plateau on semaglutide. The transition should be managed by a healthcare provider, typically starting tirzepatide at the lowest dose after discontinuing semaglutide.
Check interactions and calculate dosing for GLP-1 medications