Both Mounjaro and Wegovy are injectable medications used in weight management, but they work through different mechanisms and carry different approval statuses. Understanding how they compare across cost, dosing, efficacy data, and eligibility can help patients have more informed conversations with their prescribers.
At a Glance
| Criteria | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Active Ingredient | Tirzepatide | Semaglutide |
| FDA Approval for Weight Loss | Yes — approved as Zepbound (Nov 2023); Mounjaro approved for type 2 diabetes only | Yes — approved for chronic weight management (June 2021) |
| Mechanism | Dual GIP and GLP-1 receptor agonist | GLP-1 receptor agonist |
| List Price (per month, approx.) | ~$1,023–$1,069 (Mounjaro); ~$1,059–$1,086 (Zepbound) | ~$1,349–$1,430 |
| Dosing Schedule | Once weekly injection | Once weekly injection |
| Dose Range | 2.5 mg – 15 mg weekly | 0.25 mg – 2.4 mg weekly |
| Availability | Widely available; periodic shortages reported | Widely available; shortage designation lifted 2024 |
| Studied Average Weight Loss | ~20–22.5% body weight (SURMOUNT-1 trial) | ~15–17% body weight (STEP-1 trial) |
| Best Studied In | Adults with obesity or overweight + weight-related condition; type 2 diabetes | Adults with obesity or overweight + weight-related condition; cardiovascular risk reduction |
Active Ingredient & Mechanism
Wegovy contains semaglutide, a GLP-1 (glucagon-like peptide-1) receptor agonist. It works by mimicking the GLP-1 hormone, which signals fullness, slows gastric emptying, and reduces appetite. Mounjaro contains tirzepatide, a dual-action molecule that activates both GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors simultaneously. GIP receptor activation may provide an additive effect on fat metabolism and appetite regulation beyond GLP-1 alone, though the precise contribution is still being studied.
This mechanistic difference is considered central to why clinical trials have shown numerically higher average weight loss with tirzepatide. However, individual responses vary significantly, and mechanism alone does not predict how any particular patient will respond.
FDA Approval Status
Wegovy (semaglutide 2.4 mg) received FDA approval specifically for chronic weight management in June 2021, making it one of the first in a new class of obesity medications. It is also approved to reduce the risk of serious cardiovascular events in adults with obesity or overweight who have established cardiovascular disease, based on the SELECT trial. Mounjaro (tirzepatide) is FDA-approved for type 2 diabetes management only. For weight management, the same active ingredient is marketed as Zepbound, which received FDA approval in November 2023. Prescribers sometimes prescribe Mounjaro off-label for weight loss, but Zepbound is the on-label product for that indication.
Cost & Insurance Coverage
Both medications carry high list prices without insurance. Mounjaro and Zepbound list prices generally range from approximately $1,023 to $1,086 per month depending on dose, while Wegovy's list price ranges from approximately $1,349 to $1,430 per month. Manufacturer savings cards (Eli Lilly for Mounjaro/Zepbound; Novo Nordisk for Wegovy) may significantly reduce out-of-pocket costs for eligible commercially insured patients. Medicare Part D coverage for obesity medications remains limited under current federal policy, though this continues to be a subject of legislative discussion. Actual cost to the patient depends heavily on individual insurance plan formularies.
Compounded versions of both tirzepatide and semaglutide have circulated through telehealth and compounding pharmacies, particularly during shortage periods. The FDA has issued guidance that compounded versions are not FDA-approved and may carry different safety and efficacy profiles. Patients should consult their prescriber and verify pharmacy legitimacy before using any compounded product.
Dosing Schedule & Administration
Both medications are self-administered as subcutaneous (under-the-skin) injections once per week, on the same day each week. Mounjaro and Zepbound start at 2.5 mg weekly and can be titrated in 2.5 mg increments up to a maximum of 15 mg weekly, typically over a period of several months. Wegovy starts at 0.25 mg weekly and is titrated over approximately 16–20 weeks up to the maintenance dose of 2.4 mg weekly. Both products use pre-filled auto-injector pens. The slower titration schedules are designed to reduce gastrointestinal side effects during dose escalation.
Clinical Efficacy Data
In the SURMOUNT-1 trial, adults without diabetes who took tirzepatide 15 mg lost an average of approximately 22.5% of body weight over 72 weeks, compared to about 2.4% with placebo. The STEP-1 trial for semaglutide 2.4 mg showed an average weight loss of approximately 14.9% over 68 weeks, compared to about 2.4% with placebo. These trials were conducted in different patient populations under different protocols and were not head-to-head studies, so direct statistical comparison has limitations.
A 2023 observational study published in JAMA Internal Medicine compared real-world weight loss outcomes and found tirzepatide users lost more weight on average than semaglutide users over a 12-month period, consistent with trial data directionally. However, no large-scale randomized head-to-head trial between the two drugs for weight loss has been published as of this writing.
Side Effects & Safety Profile
Both medications share a similar side effect profile due to their overlapping GLP-1 mechanism. The most common side effects for both include nausea, vomiting, diarrhea, constipation, and abdominal discomfort, particularly during dose escalation. These effects are generally transient and tend to diminish as the body adjusts. Both drugs carry a boxed warning for the risk of thyroid C-cell tumors based on rodent studies; neither is recommended for patients with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Rare but serious risks for both include pancreatitis, gallbladder disease, and acute kidney injury (often secondary to dehydration).
Because tirzepatide also activates GIP receptors, its full long-term safety differentiation from semaglutide is still being characterized in ongoing post-market studies. Both drugs are contraindicated in pregnancy. Patients should review the full prescribing information with their healthcare provider.
Availability
Wegovy experienced significant supply shortages beginning in 2022 following its launch, which drove widespread off-label use of the lower-dose Ozempic (semaglutide for diabetes). The FDA removed Wegovy from its drug shortage list in 2024, indicating supply has largely stabilized. Mounjaro similarly experienced demand-driven shortages. Both products are now broadly available through major retail and specialty pharmacies, though specific doses may still face intermittent regional availability constraints. Patients should confirm availability at their local pharmacy before initiating or changing therapy.
Key Takeaway
The core difference between Mounjaro (tirzepatide) and Wegovy (semaglutide) for weight loss lies in their mechanisms: Wegovy targets GLP-1 receptors alone, while Mounjaro's active ingredient targets both GLP-1 and GIP receptors. Clinical trial data shows numerically greater average weight loss with tirzepatide, and Wegovy carries an additional FDA-approved indication for cardiovascular risk reduction. Cost, insurance coverage, individual health history, and prescriber judgment are all factors that determine which option — if either — is appropriate for a given patient.