Key takeaways
- In trials, semaglutide (Wegovy) averaged about 15% body-weight loss and tirzepatide (Zepbound) about 15–21% depending on dose, with tirzepatide winning the only head-to-head trial, 20.2% vs 13.7%.
- Those are trial averages. In everyday practice the average is closer to 9%, not because the drugs are weaker, but because people stop early or never reach the full dose.
- The single biggest lever on your result isn’t the brand. It’s reaching and staying on an effective dose, which comes down to access, support, and cost.
What the trials show: the real numbers
Every weight-loss headline you’ve seen traces back to a handful of large randomized trials. Here’s what they reported, side by side. These are average losses over roughly 15–18 months at the full studied dose, versus placebo.
| Trial | Drug & dose | Avg. weight loss | Placebo |
|---|---|---|---|
| STEP 1 | Semaglutide 2.4 mg (Wegovy) | −14.9% | −2.4% |
| SURMOUNT-1 | Tirzepatide 5 mg (Zepbound) | −15.0% | −3.1% |
| SURMOUNT-1 | Tirzepatide 10 mg | −19.5% | −3.1% |
| SURMOUNT-1 | Tirzepatide 15 mg | −20.9% | −3.1% |
| SURMOUNT-5 | Tirzepatide vs semaglutide (head-to-head) | −20.2% vs −13.7% | n/a |
A few things worth pulling out of that table:
Semaglutide (Wegovy): about 15%, and most people respond
In STEP 1, semaglutide 2.4 mg produced an average 14.9% weight loss at 68 weeks. Just as important as the average: 86% of participants lost at least 5% of their body weight (the threshold where meaningful health benefits start), so this wasn’t a case of a few big responders dragging up the mean.
Source: STEP 1, NEJM 2021 (NEJMoa2032183) · 1,961 participants · funded by Novo Nordisk (disclosed per our methodology)
Tirzepatide (Zepbound): dose-dependent, up to ~21%
Tirzepatide’s effect climbs with dose: about 15% at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg (the figures Lilly reported as “up to 22.5%” come from a different statistical estimand, the most-optimistic way of counting). Roughly nine in ten participants lost weight. The takeaway: the higher doses deliver more, which is exactly why being able to titrate up matters.
Source: SURMOUNT-1, NEJM 2022 (NEJMoa2206038) · funded by Eli Lilly
Head-to-head: tirzepatide came out ahead
In the first trial to put the two drugs against each other at maximum tolerated doses, tirzepatide produced 20.2% average loss versus 13.7% for semaglutide, a real, statistically significant gap of about 6.5 points. (Worth noting it was funded by tirzepatide’s maker; the result is consistent with the separate trials above.)
Source: SURMOUNT-5, NEJM 2025 (NEJMoa2416394) · 751 participants · funded by Eli Lilly
The number the brochures don’t show: real-world results
Here’s where most articles stop, and where this one keeps going. Trial averages come from people who get the drug for free, are coached to stay on it, and are titrated to the full dose. Real life is messier.
In everyday practice, the average is closer to 9%
A study of nearly 8,000 real patients found an average one-year loss of 8.7%, well below the trial figures. But that average hides the real story: people who stayed on treatment lost 11.9%, while those who stopped early lost just 3.6%. And 80% never reached a high maintenance dose. The drugs weren’t weaker; people just didn’t get a full course of them.
Source: Gasoyan H et al., Obesity 2025 (doi:10.1002/oby.24331); 7,881 adults, Cleveland Clinic
So the gap between “20%” and “9%” isn’t about which brand you choose. It’s about two things you can influence: reaching an effective dose, and not getting forced off the drug. Both come down to access, clinical support, and cost, which is why those weigh so heavily in how we rank providers.
What drives your result
Lining up everything above, the factors that move the needle, roughly in order:
- Staying on the medication. By far the biggest lever (11.9% vs 3.6% in real-world data).
- Reaching an adequate dose. Higher doses worked better in the trials; 80% of real patients never got there.
- Which drug. Tirzepatide edged semaglutide head-to-head, but both are effective.
- Your starting point and biology. Individual response varies; trial figures are averages, not promises.
- Lifestyle support. Every trial paired the drug with diet and activity coaching.
Notice that the medication brand is only #3. The top two are about access and continuity, which is the part a good provider helps with and a bad one quietly sabotages.
Will it cost more to lose more?
Not necessarily, and the sticker prices can mislead. A “$39/month” membership often bills the drug separately, while an all-in compounded option or an insurance copay can land lower. Because the dose you can sustain matters more than the brand, the right comparison is the real monthly cost of staying on an effective dose, not the advertised starting price.
Why we recommend them: the highest score in our independent rubric for medical supervision and insurance support, the two things that most determine whether you reach and keep an effective dose. We take no money from Form Health; the link goes to their own site.
Frequently asked questions
Is 20% weight loss realistic for me?
It’s the trial average for tirzepatide at the top dose, but trial conditions are ideal. Real-world averages are lower (around 9%), mostly because people stop early or don’t reach a full dose. If you reach and maintain an effective dose, results closer to the trial figures are achievable; individual response still varies.
Which drug gives more weight loss, Wegovy or Zepbound?
In the only head-to-head trial (SURMOUNT-5), tirzepatide (Zepbound) produced more average loss, 20.2% vs 13.7%. Both are highly effective; the right one for you also depends on cost, coverage, side effects, and whether you have a cardiovascular history. See our full Wegovy vs. Zepbound comparison.
How long until I see results?
Trials measure final results at roughly 15–18 months, with weight coming off steadily over that period as the dose is increased. Early weeks are usually about tolerating dose increases more than dramatic loss. Patience through titration is part of why staying on it matters.
Do compounded versions work as well?
There’s no large head-to-head trial of compounded versions against the brand-name drugs; the trial figures here are all from FDA-approved Wegovy and Zepbound. Compounded products aren’t FDA-approved and quality varies by pharmacy; we cover the trade-offs in brand vs. compounded.
- STEP 1. Wilding JPH et al., Once-Weekly Semaglutide in Adults with Overweight or Obesity, New England Journal of Medicine 2021 (NEJMoa2032183); 1,961 adults, 68 weeks. Mean weight change −14.9% with semaglutide 2.4 mg vs −2.4% placebo; 86% reached ≥5% loss. Funded by Novo Nordisk (Wegovy's manufacturer).
- SURMOUNT-1. Jastreboff AM et al., Tirzepatide Once Weekly for the Treatment of Obesity, New England Journal of Medicine 2022 (NEJMoa2206038); 72 weeks. Mean weight change −15.0% / −19.5% / −20.9% at 5/10/15 mg (treatment-regimen estimand) vs −3.1% placebo; up to −22.5% under the efficacy estimand. Funded by Eli Lilly (Zepbound's manufacturer).
- SURMOUNT-5. Head-to-head randomized controlled trial, New England Journal of Medicine 2025 (NEJMoa2416394); 751 adults, 72 weeks, maximum tolerated doses. Tirzepatide −20.2% vs semaglutide −13.7%. Funded by Eli Lilly.
- Real-world cohort. Gasoyan H et al., Obesity 2025 (doi:10.1002/oby.24331); Cleveland Clinic electronic-health-record cohort of 7,881 adults. Mean one-year weight change 8.7% overall; 11.9% among those who stayed on treatment, 3.6% among early discontinuers; 80.8% used low maintenance dosages.
- FDA prescribing information: Wegovy (semaglutide), Zepbound (tirzepatide).
This article was produced using our 31-point scoring methodology; every primary source we cite across the site is collected in our consolidated bibliography. We analyze published research and consumer reviews; we do not personally test medical products. This is not medical advice. Consult a licensed clinician.