For years, people choosing between Wegovy (semaglutide) and Mounjaro/Zepbound (tirzepatide) had to rely on side-by-side comparisons of separate clinical trials — which is a bit like judging two runners by timing them on different tracks. In early 2025, that changed. The SURMOUNT-5 trial gave us the first true head-to-head data, and the results were striking enough to reshape how clinicians and patients think about these two medications. Here's everything you need to know, explained clearly.
The Two Contenders: A Quick Recap
Before diving into the matchup, it helps to understand what makes these drugs different at a biological level.
Wegovy (semaglutide) is a GLP-1 receptor agonist. It mimics the glucagon-like peptide-1 hormone, which signals fullness, slows gastric emptying, and reduces appetite. It's been on the market since 2021 for weight management and has a robust safety record backed by multiple large trials.
Mounjaro/Zepbound (tirzepatide) is a dual GIP and GLP-1 receptor agonist. By activating two hormone pathways simultaneously — both GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) — it appears to produce stronger appetite suppression and greater metabolic effects. Mounjaro is approved for type 2 diabetes; Zepbound is the same molecule approved specifically for weight loss.
Think of semaglutide as a powerful single-engine plane and tirzepatide as a twin-engine version. Both get you where you're going, but one has notably more thrust.
What the Individual Trials Showed
Before SURMOUNT-5, here's what each drug demonstrated on its own:
- Semaglutide (STEP trials): Participants lost an average of 13.7% of body weight over 68 weeks at the 2.4 mg weekly dose.
- Tirzepatide (SURMOUNT trials): Participants lost an average of 20.2% of body weight — with some reaching doses of 15 mg weekly.
On paper, that's already a meaningful gap. But different participant populations, different trial designs, and different time frames made a direct comparison tricky. SURMOUNT-5 solved that problem.
SURMOUNT-5: The Head-to-Head Trial That Changed Everything
Published in early 2025, SURMOUNT-5 was a randomized, double-blind, head-to-head trial directly comparing tirzepatide (up to 15 mg weekly) against semaglutide (up to 2.4 mg weekly) in adults with obesity or overweight plus at least one weight-related condition. Neither participants nor researchers knew who was taking which drug during the trial — gold-standard methodology.
The headline result: tirzepatide produced 47% greater relative weight loss compared to semaglutide.
In absolute terms, tirzepatide participants lost approximately 20.2% of their body weight versus roughly 13.7% for semaglutide. For a person weighing 250 lbs (113 kg), that difference translates to about 16 extra pounds lost on tirzepatide.
Beyond the primary endpoint, SURMOUNT-5 also found that tirzepatide users were significantly more likely to reach the 15%, 20%, and 25% body weight loss thresholds — benchmarks that are increasingly linked to meaningful improvements in metabolic health, blood pressure, and joint pain.
Important context: SURMOUNT-5 enrolled people without type 2 diabetes. Results may differ for people managing both obesity and diabetes, where the relative performance gap between the two drugs has historically been smaller. Always discuss your individual health profile with your prescriber before making a medication decision.
Side Effects: How Do They Compare?
Both medications share a similar side effect profile because they work through overlapping mechanisms. The most common issues are gastrointestinal:
- Nausea (most common, especially early in treatment)
- Vomiting
- Diarrhea or constipation
- Acid reflux or burping
In SURMOUNT-5, rates of GI side effects were broadly similar between the two drugs, though tirzepatide users reported slightly higher rates of nausea at maximum doses. Both drugs use gradual dose escalation schedules specifically to minimize these effects. Most people find that GI symptoms improve significantly after the first few weeks.
Serious but rare risks — including pancreatitis, gallbladder issues, and a theoretical thyroid concern based on animal data — apply to both medications and should be discussed with your doctor.
Cost and Access: The Practical Reality
Efficacy data is only half the story. For many people, what matters most is whether they can actually get and afford the medication.
- Wegovy list price runs approximately $1,349/month without insurance. Coverage has expanded significantly since 2024, particularly following Medicare Part D changes.
- Zepbound (tirzepatide for weight loss) list price is approximately $1,059/month without insurance — notably lower than Wegovy despite stronger efficacy data.
- Manufacturer savings programs can bring costs down dramatically for commercially insured patients. Eli Lilly's savings card for Zepbound and Novo Nordisk's program for Wegovy are both worth investigating.
- Compounded semaglutide and tirzepatide became widely available during shortage periods and remain an option at significantly lower cost in some markets, though regulatory status varies and quality can differ between compounders.
Supply chain issues that plagued both drugs between 2023 and 2025 have largely stabilized, though availability can still vary by region and pharmacy.
Who Might Still Choose Wegovy?
Given the head-to-head data, it's reasonable to ask: is there still a case for semaglutide? The answer is yes, for several reasons:
- Longer track record: Semaglutide has been used for weight management since 2021 and for diabetes (as Ozempic) since 2017. Some clinicians and patients prefer its longer safety history.
- Individual response varies: A meaningful percentage of semaglutide users achieve excellent results — 15% or more body weight loss — and may not need the additional mechanism of tirzepatide.
- Tolerability: Some individuals tolerate semaglutide better than tirzepatide, or vice versa. If you've tried one and struggled with side effects, the other may suit you better.
- Insurance coverage: Depending on your plan, one drug may be covered while the other isn't. That financial reality often drives the decision more than efficacy data alone.
- Cardiovascular data: The SELECT trial demonstrated that semaglutide reduces major cardiovascular events in people with existing cardiovascular disease — a landmark finding. Comparable cardiovascular outcome data for tirzepatide is still accumulating.
How to Use This Information in a Real Conversation With Your Doctor
The SURMOUNT-5 results are a useful starting point, but they don't make the decision for you. Here's how to have a productive conversation with your prescriber:
- Ask about your specific health goals — if you need to lose 15% of body weight to improve a health condition, versus 25%, that changes the math.
- Discuss your history with GI sensitivity, as this can influence which drug you're more likely to tolerate.
- Review your insurance formulary together before assuming one drug is out of reach.
- Ask about cardiovascular risk — if you have existing heart disease, the SELECT data for semaglutide may be particularly relevant to your situation.
The best GLP-1 medication is ultimately the one you can access, afford, tolerate, and stay on consistently. Adherence is the variable that matters most in real-world outcomes.
Estimate Your Personal Results Before You Decide
One thing that often gets lost in clinical trial summaries is the translation to your own body. An average 20.2% weight loss sounds meaningful, but what does that actually look like at your current weight? How does it compare to your goal?
That's exactly what our free calculator is designed to help you explore. Use the GLP-1 Weight Loss Calculator at GLP1Calc to plug in your current weight, your target, and your medication of interest — and get a personalized projection based on the same clinical trial data discussed in this article.
It won't replace a conversation with your doctor, but it will give you a concrete, numbers-based starting point that makes that conversation much more productive.
The Bottom Line
The SURMOUNT-5 trial settled the question that indirect comparisons couldn't: in a head-to-head test, tirzepatide produces significantly more weight loss than semaglutide — about 47% more in relative terms. For people whose primary goal is maximum weight reduction, that's a clinically meaningful difference.
That said, both drugs are effective, both are generally well-tolerated, and both have helped millions of people achieve weight loss that diet and exercise alone couldn't deliver. The right choice depends on your health profile, your goals, your insurance situation, and how your body responds.
Use the data. Have the conversation. And remember that the best medication is the one that works for your life — not just the one that wins on a spreadsheet.