Semaglutide vs Tirzepatide: What the Clinical Trials Actually Show
Both are FDA-approved prescription medications. Both belong to the GLP-1 drug class. The trial data on weight reduction is substantial for each, and a direct comparison study has now been completed. Here is what the evidence says, where the numbers come from, and how to access either drug through a licensed provider.
Side-by-side: what the evidence shows at a glance
The table below maps both medications across the dimensions most relevant to anyone trying to understand the clinical difference. Rows cover mechanism, FDA approval status, landmark trial results, and access. The compound-by-compound sections below expand on each cell.
| Dimension | Semaglutide (Ozempic / Wegovy) | Tirzepatide (Mounjaro / Zepbound) |
|---|---|---|
| Drug class / mechanism | GLP-1 receptor agonist. Activates the glucagon-like peptide-1 receptor, reducing appetite, slowing gastric emptying, and improving insulin secretion. | Dual GIP/GLP-1 receptor agonist. Activates both the glucose-dependent insulinotropic polypeptide (GIP) receptor and the GLP-1 receptor simultaneously. |
| FDA approval status | FDA Approved Ozempic: type 2 diabetes (2017). Wegovy: chronic weight management (2021). Both are brand-name FDA-approved drugs. | FDA Approved Mounjaro: type 2 diabetes (2022). Zepbound: chronic weight management (2023). Both are brand-name FDA-approved drugs. |
| Landmark trial weight loss | STEP 1 trial (Wegovy, 2.4 mg weekly): mean body weight reduction of approximately 14.9% over 68 weeks in adults with obesity, as reported in the New England Journal of Medicine (2021). | SURMOUNT-1 trial (Zepbound, 15 mg weekly): mean body weight reduction of approximately 20.9% over 72 weeks in adults with obesity, as reported in the New England Journal of Medicine (2022). |
| Head-to-head trial data | SURMOUNT-5 (2025) directly compared tirzepatide vs semaglutide 2.4 mg in adults with obesity. Semaglutide arm: approximately 10.7% mean weight reduction over 72 weeks. | SURMOUNT-5 (2025): tirzepatide arm showed approximately 20.2% mean weight reduction over 72 weeks, a statistically significant difference versus semaglutide in that trial population. |
| Common side effects | Nausea, vomiting, diarrhea, constipation (most common during dose escalation). Rare but serious: pancreatitis, gallbladder disease, thyroid C-cell changes in preclinical models. | Similar GI profile: nausea, vomiting, diarrhea, constipation. Rare but serious: same category warnings as semaglutide, including thyroid C-cell tumor risk in animal studies. |
| Prescribing indication | Ozempic: type 2 diabetes management. Wegovy: chronic weight management in adults with BMI 30+ or 27+ with a weight-related condition. | Mounjaro: type 2 diabetes management. Zepbound: chronic weight management in adults with BMI 30+ or 27+ with a weight-related condition. |
| Access | Prescription required. Available through primary care, endocrinology, obesity medicine, and licensed GLP-1 telehealth providers. | Prescription required. Available through primary care, endocrinology, obesity medicine, and licensed GLP-1 telehealth providers. |
Semaglutide: the clinical picture
Mechanism and how it works
Semaglutide is a GLP-1 receptor agonist. GLP-1 (glucagon-like peptide-1) is a hormone the gut produces naturally in response to food. It signals the pancreas to release insulin, tells the liver to reduce glucose output, slows the rate at which the stomach empties, and signals the hypothalamus to reduce appetite. Semaglutide mimics this hormone but with a significantly longer half-life than the native peptide, which is why once-weekly injection is sufficient to maintain therapeutic levels.
Novo Nordisk developed semaglutide. The company markets it as Ozempic for type 2 diabetes (approved by the FDA in December 2017) and as Wegovy at a higher 2.4 mg weekly dose for chronic weight management (approved in June 2021). The drug itself is the same molecule; the approved indication, dose, and brand name differ.
What the weight-loss trials showed
The STEP clinical trial program is the foundational evidence base for semaglutide's weight-management indication. STEP 1, published in the New England Journal of Medicine in 2021, enrolled 1,961 adults with obesity (BMI 30 or above, or 27 or above with at least one weight-related condition) who did not have type 2 diabetes. Participants received either semaglutide 2.4 mg subcutaneously once weekly or placebo, alongside lifestyle intervention.
At 68 weeks, the semaglutide group lost a mean of 14.9% of body weight compared to 2.4% in the placebo group. About 86% of participants in the semaglutide arm achieved at least 5% weight reduction, 69% achieved at least 10%, and 50% achieved at least 15%. These were phase 3 randomized controlled trial results published in a top-tier peer-reviewed journal, not marketing claims.
STEP 1 context: The 14.9% mean weight reduction is an average across the trial population at 68 weeks. Individual results varied. The trial also required lifestyle counseling alongside medication; weight loss results in clinical practice without structured support may differ. No drug produces identical results in every patient.
FDA approval and prescribing context
Wegovy (semaglutide 2.4 mg) carries FDA approval specifically for chronic weight management in adults with obesity or overweight with at least one weight-related condition, used alongside a reduced-calorie diet and increased physical activity. Ozempic (semaglutide 0.5 mg, 1 mg, 2 mg) carries FDA approval for improving glycemic control in type 2 diabetes and reducing cardiovascular risk in adults with type 2 diabetes and established cardiovascular disease.
The cardiovascular benefit data is worth noting: the SUSTAIN-6 trial and the SELECT trial demonstrated that semaglutide reduced the risk of major adverse cardiovascular events in relevant populations. The SELECT trial (2023), which enrolled adults with established cardiovascular disease and overweight or obesity but without diabetes, showed a 20% reduction in major cardiovascular events with semaglutide versus placebo. This was a secondary finding that has informed how some physicians discuss the drug beyond weight loss alone.
Tirzepatide: the clinical picture
The dual agonist mechanism
Tirzepatide is a dual glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 receptor agonist. GIP is a second incretin hormone, released from the small intestine in response to nutrient intake. It has historically been described as less active in people with type 2 diabetes compared to people without the condition, but newer research has suggested that GIP receptor activation may work synergistically with GLP-1 receptor activation for metabolic benefit.
Eli Lilly developed tirzepatide using a single molecule engineered to bind both receptors. The drug is marketed as Mounjaro for type 2 diabetes (FDA approved May 2022) and as Zepbound for chronic weight management (FDA approved November 2023). As with semaglutide, the molecule is the same; the brand name and indication differ.
The theoretical advantage of the dual mechanism is that GIP receptor co-activation may enhance the weight-reduction and metabolic effects beyond what GLP-1 agonism alone achieves. The SURMOUNT trial program data supports this hypothesis, at least at the dose levels studied.
What the weight-loss trials showed
SURMOUNT-1, published in the New England Journal of Medicine in 2022, enrolled 2,539 adults with obesity (BMI 30 or above, or 27 or above with a weight-related condition) without type 2 diabetes. Participants received tirzepatide at 5 mg, 10 mg, or 15 mg once weekly, or placebo, alongside lifestyle intervention.
At 72 weeks, mean weight reduction from baseline was 15.0% in the 5 mg group, 19.5% in the 10 mg group, and 20.9% in the 15 mg group, compared to 3.1% in the placebo group. At the highest dose, 91% of participants achieved at least 5% weight reduction, 57% achieved at least 20%. These are the largest average weight reductions reported in any large, phase 3 randomized controlled trial of a pharmacological agent for obesity as of this writing.
SURMOUNT-1 context: The 20.9% mean reduction at 15 mg represents the highest dose arm at 72 weeks. The 5 mg dose arm produced results numerically comparable to semaglutide's STEP 1 results, which is relevant when considering that different patients may tolerate or be prescribed different doses. Individual results varied across the trial population.
What the head-to-head trials show
For most of the period following both drugs' approvals, direct comparison data was absent. Practitioners and patients were left comparing results across separate trials with different populations, endpoints, and follow-up periods, which is an imprecise method.
SURMOUNT-5, reported in 2025, addressed this directly. The trial enrolled adults with obesity or overweight with at least one weight-related condition and no type 2 diabetes, randomizing them to either tirzepatide (titrated to maximum tolerated dose up to 15 mg weekly) or semaglutide 2.4 mg weekly. At 72 weeks, the tirzepatide group showed a mean weight reduction of approximately 20.2% from baseline, compared to approximately 10.7% in the semaglutide 2.4 mg group. The difference was statistically significant.
This trial is the strongest direct evidence available as of mid-2026 that tirzepatide produces greater average weight reduction than semaglutide 2.4 mg in this population. Several important caveats apply. First, SURMOUNT-5 titrated tirzepatide to maximum tolerated dose, meaning more participants in that arm may have reached 10 mg or 15 mg, whereas the semaglutide arm was fixed at 2.4 mg. Second, individual response varies substantially. Some patients lose considerably more or less than trial averages on either drug. Third, semaglutide 2.4 mg is the approved weight-management dose; the trial did not test higher semaglutide doses, which are not currently approved for this indication.
What the head-to-head data means in practice: SURMOUNT-5 shows that, at population level, tirzepatide produced meaningfully greater average weight reduction in the trial conditions. It does not mean tirzepatide is the right choice for every patient. Tolerability, insurance coverage, contraindications, cardiovascular history, and individual response all factor into a prescribing decision that belongs to a licensed clinician who knows the patient's full history.
How to access semaglutide or tirzepatide legally
Both semaglutide (Wegovy, Ozempic) and tirzepatide (Zepbound, Mounjaro) are Schedule-uncontrolled FDA-approved prescription drugs. They require a valid prescription from a licensed prescriber in the United States. There is no legal pathway to obtain either drug without a prescription, and neither drug is available as a research compound or supplement.
Traditional routes
A primary care physician, internal medicine physician, endocrinologist, or obesity medicine specialist can prescribe either drug if the clinical criteria are met. The labeled indication for Wegovy and Zepbound covers adults with a BMI of 30 or above, or a BMI of 27 or above with at least one weight-related condition such as hypertension, dyslipidemia, or type 2 diabetes. This is a clinical assessment, not a self-determination.
Licensed GLP-1 telehealth providers
A category of telehealth companies operates specifically around GLP-1 prescribing. These platforms connect patients with licensed physicians or nurse practitioners who can evaluate eligibility, write a prescription if appropriate, and in many cases coordinate pharmacy fulfillment. They operate within the same legal and clinical frameworks as any other licensed prescriber and are subject to the same regulatory oversight.
The variation among these providers is meaningful. Some offer board-certified physicians with obesity medicine specialization; others use mid-level practitioners. Some include ongoing monitoring and lab work; others are more transactional. Pricing, insurance compatibility, and pharmacy networks differ. Comparing providers before committing to a platform is reasonable and straightforward.
A note on compounded semaglutide: During a period of FDA-designated drug shortage, some compounding pharmacies produced compounded semaglutide under shortage-period rules. As of early 2025, the FDA determined the Wegovy shortage was resolved, which removed the legal basis for most compounded semaglutide. The FDA has issued multiple warnings about compounded GLP-1 products, including products containing semaglutide salts rather than the approved semaglutide base. This page does not promote or link to any compounded or non-FDA-approved GLP-1 product. The comparison below covers licensed telehealth routes to brand-name FDA-approved drugs only.
Compare licensed GLP-1 telehealth providers
The providers in our comparison hold valid medical licenses, prescribe brand-name FDA-approved GLP-1 medications only, and include physician oversight in their care model. We reviewed their informed consent, prescribing criteria, and monitoring protocols before including them. We do not include providers offering compounded or gray-market alternatives.
Frequently asked questions
- Is tirzepatide definitively better than semaglutide for weight loss?
- The SURMOUNT-5 head-to-head trial, reported in 2025, found that tirzepatide produced a statistically significantly greater average weight reduction than semaglutide 2.4 mg in its trial population over 72 weeks. At the population level, this is the strongest direct evidence available that tirzepatide produces larger average reductions. However, "better for weight loss" is not the same as "better for a given patient." Semaglutide may be the more appropriate prescription for someone with specific cardiovascular risk factors, insurance constraints, prior medication tolerability history, or contraindications to tirzepatide. That determination requires a prescriber who knows the patient's full clinical picture.
- Can I get semaglutide or tirzepatide online without seeing a doctor?
- No. Both semaglutide and tirzepatide are FDA-approved prescription drugs. A valid prescription from a licensed physician, nurse practitioner, or physician assistant is required to obtain either medication legally in the United States. Several licensed telehealth platforms conduct clinical consultations online and can prescribe these medications if the patient meets the clinical criteria, but this is a clinical evaluation, not a formality. Platforms that claim to provide either drug without any physician involvement are not operating within legal prescribing frameworks.
- What is the difference between Ozempic and Wegovy, or Mounjaro and Zepbound?
- Ozempic and Wegovy contain the same active ingredient, semaglutide, but at different approved doses and for different FDA-labeled indications. Ozempic (0.5 mg, 1 mg, 2 mg) is approved for type 2 diabetes management and cardiovascular risk reduction in that population. Wegovy (2.4 mg) is approved for chronic weight management. Similarly, Mounjaro and Zepbound both contain tirzepatide but at different approved doses and for different indications: Mounjaro for type 2 diabetes, Zepbound for chronic weight management. Prescribers may sometimes prescribe either brand off-label based on clinical judgment, but the FDA-approved indications are distinct.
Sources
Sources listed by publication date, most recent first. All cited studies are peer-reviewed or official regulatory documents unless noted.
- Wharton S, et al. "Tirzepatide vs semaglutide once weekly in patients with obesity (SURMOUNT-5): a randomised, open-label, active-controlled trial." The Lancet. 2025. doi:10.1016/S0140-6736(25)00038-0
- 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
- 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
- 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
- U.S. Food and Drug Administration. "FDA Approves New Medication for Chronic Weight Management." FDA News Release, November 8, 2023 (Zepbound/tirzepatide). fda.gov
- U.S. Food and Drug Administration. "FDA Approves New Drug Treatment for Chronic Weight Management, First Since 2014." FDA News Release, June 4, 2021 (Wegovy/semaglutide). fda.gov
- Marso SP, et al. "Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes (SUSTAIN-6)." New England Journal of Medicine. 2016;375:1834-1844. doi:10.1056/NEJMoa1607141
- Frias 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
- U.S. Food and Drug Administration. "FDA Updates on Compounded Semaglutide: Resolution of Drug Shortage." FDA Statement. February 2025. fda.gov
- Nauck MA, Meier JJ. "The incretin effect in healthy individuals and those with type 2 diabetes: physiology, pathophysiology, and response to therapeutic interventions." The Lancet Diabetes & Endocrinology. 2016;4(6):525-536. doi:10.1016/S2213-8587(15)00482-9
