Wegovy vs Mounjaro: Comparing Semaglutide and Tirzepatide for Weight Loss
The comparison patients actually make
Patients comparing Wegovy and Mounjaro are typically in one of two situations:
- They are starting GLP-1 therapy and trying to decide between the two drugs
- They have been on one drug and are considering switching to the other
This is complicated by the fact that Mounjaro is technically approved for T2D, not obesity (Zepbound is the obesity-indicated tirzepatide brand). In practice, many patients receive Mounjaro for weight management purposes — either because they have T2D, or off-label.
This article compares the two drugs directly for weight loss outcomes, regardless of which brand name is used.
Mechanism: one receptor vs two
Wegovy/semaglutide: GLP-1 receptor agonist. Activates GLP-1 receptors in the pancreas (insulin secretion, glucagon suppression), gut (gastric slowing), and brain (appetite suppression, reward circuit modulation).
Mounjaro/tirzepatide: Dual GIP/GLP-1 receptor agonist. Activates both GLP-1 receptors (same mechanisms as semaglutide) and GIP receptors. GIP activation appears to enhance appetite suppression and fat metabolism through complementary pathways to GLP-1.
Why this matters: The dual agonism of tirzepatide produces greater average weight loss than semaglutide in clinical trials. This is the primary clinical reason to choose tirzepatide over semaglutide if weight loss is the primary goal. For a full breakdown of the molecular differences, see the tirzepatide vs semaglutide comparison.
Weight loss: what the head-to-head data shows
SURMOUNT-5 trial (2024): The most reliable comparison — a direct RCT of tirzepatide (Zepbound 10/15 mg) vs semaglutide (Wegovy 2.4 mg) in obese adults without T2D over 72 weeks.
| Endpoint | Tirzepatide | Semaglutide | Difference |
|---|---|---|---|
| Mean weight loss | 20.2% | 13.7% | 6.5 percentage points |
| Patients losing ≥15% | 66% | 42% | +24 percentage points |
| Patients losing ≥20% | 48% | 25% | +23 percentage points |
| Patients losing ≥25% | 31% | 13% | +18 percentage points |
Summary: Tirzepatide produces approximately 47% more relative weight loss than semaglutide. The difference is clinically substantial, not marginal.
Side effects: which drug is better tolerated?
Clinical trial data:
| Side effect | Wegovy (STEP 1) | Mounjaro/Zepbound (SURMOUNT-1, 15 mg) |
|---|---|---|
| Nausea | 44% | 32% |
| Vomiting | 24% | 18% |
| Diarrhoea | 30% | 23% |
| Constipation | 24% | 26% |
| Abdominal pain | 22% | 9% |
Tirzepatide appears modestly better tolerated despite superior efficacy — lower rates of nausea, vomiting, diarrhoea, and abdominal pain. For trial-by-trial side effect rates across all GLP-1 drugs, see the GLP-1 side effects comparison. This is a counter-intuitive finding (typically more potent drugs have more side effects) and is attributed by some researchers to the GIP component partially counteracting some GLP-1-mediated GI effects.
Constipation rates are roughly similar between the two drugs.
Cost comparison
| Wegovy | Mounjaro | |
|---|---|---|
| List price (month) | ~$1,350 | ~$1,060 |
| NovoCare/savings card | ~$499 for qualifying patients | LillyDirect: ~$550 |
| Insurance (commercial, prior auth) | ~$25–75 copay (if covered) | ~$25–75 copay (if covered for T2D) |
| Compounded semaglutide | $150–$300/month | N/A for Wegovy specifically |
| Compounded tirzepatide | N/A for Mounjaro specifically | $299–$449/month |
Mounjaro has a lower list price than Wegovy. Insurance coverage for Mounjaro is often better than Wegovy because T2D drug coverage is more standardised than obesity drug coverage. Non-T2D patients seeking Mounjaro for weight loss off-label may face coverage challenges.
Injection and administration
Both are once-weekly subcutaneous injections that follow a structured dose escalation schedule. Practical differences:
- Wegovy comes in pre-filled auto-injector pens (one dose per pen)
- Mounjaro/Zepbound also comes in pre-filled auto-injector pens
- Injection technique is the same for both
- Pen sizes differ — Mounjaro pens are slightly different in grip and needle deployment from Wegovy pens, but patient experience with both is generally similar
FDA-approved indications
| Wegovy | Mounjaro | |
|---|---|---|
| Obesity | ✓ Approved (June 2021) | ✗ Not approved (Zepbound is the obesity brand) |
| T2D | ✗ Not approved (Ozempic is the T2D brand) | ✓ Approved (May 2022) |
| ASCVD risk reduction | ✓ Approved (January 2024) | ✗ Not yet approved (trial ongoing) |
| HFpEF | ✓ Approved (2024) | ✗ Not yet approved (trial submitted) |
Note: Mounjaro is the same molecule as Zepbound. Patients who need the obesity indication are prescribed Zepbound (not Mounjaro) when using tirzepatide for weight management. Similarly, Wegovy and Ozempic are the same semaglutide molecule — see Ozempic vs Wegovy: same drug for how the two brands differ. However, many patients in practice receive Mounjaro off-label or via the LillyDirect programme regardless of this distinction.
How to choose between them
Choose semaglutide (Wegovy) if
- You have established cardiovascular disease (SELECT trial MACE reduction data applies)
- Insurance covers Wegovy but not Zepbound/Mounjaro for your indication
- You have kidney disease (FLOW trial renal protection data supports semaglutide)
- Prior sleep apnoea approved indication matters for your coverage
- Cost is a limiting factor and compounded semaglutide (lower cost) is your access pathway
Choose tirzepatide (Mounjaro/Zepbound) if
- Maximising weight loss is the priority (consistent ~47% better average outcomes in head-to-head data)
- You have T2D (insurance typically covers Mounjaro for T2D)
- Tolerability matters (tirzepatide shows modestly lower GI side effect rates)
- Your BMI is very high and you need maximum absolute weight loss
For patients without T2D choosing between cash-pay compounded versions: Tirzepatide costs more but produces more weight loss. For higher-BMI patients, the larger absolute weight loss from tirzepatide often justifies the higher price per month.
Summary
Wegovy (semaglutide 2.4 mg) and Mounjaro (tirzepatide) are different molecules with different mechanisms. Tirzepatide produces approximately 47% more relative weight loss in the only head-to-head RCT, has modestly better tolerability, and lower list price. Semaglutide has more approved indications, longer safety follow-up, and is often the better choice for cardiovascular and kidney disease patients. The "right" drug depends on goals, comorbidities, insurance, and cost access.