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How well do GLP-1 drugs work? In the large trials behind FDA approval of GLP-1 for weight loss, adults without diabetes lost about 15% of body weight on average over 68 weeks with Wegovy (semaglutide) and 15% to 21% over 72 weeks with Zepbound (tirzepatide), compared with 2% to 3% on placebo. Daily tablets produced about 11% to 14%. People with type 2 diabetes lost less, and weight usually came back after stopping. These are group averages: some people lost more than 20%, while others lost under 5%.
Peptide Labs does not sell Wegovy, Zepbound, Ozempic, Mounjaro or any prescription drug. This article is general information, not medical advice. For background on how these medicines act, see what GLP-1 is.
Key Takeaways
- STEP 1 (Wegovy, 1,961 adults, 68 weeks, Novo Nordisk): average weight change -14.9% vs -2.4% on placebo.
- SURMOUNT-1 (Zepbound, 2,539 adults, 72 weeks, Eli Lilly): -15.0% to -20.9% depending on strength vs -3.1%.
- In the head-to-head SURMOUNT-5 trial, tirzepatide averaged -20.2% and semaglutide -13.7% over 72 weeks.
- Ozempic and Mounjaro are diabetes medicines; weight loss in their diabetes trials was smaller.
- After stopping, most lost weight returned: about two-thirds within a year in the STEP 1 extension.
- About 1 in 7 people in STEP 1 lost less than 5% of body weight.
GLP-1 for weight loss: average results from the main trials
The table lists the main published trials of the approved weight-management brands and related studies. Each compared the drug with placebo unless noted, alongside diet and activity advice. Trials differed in who took part, how long they ran and how they handled people who stopped, so the rows should not be ranked against each other.
| Trial | Drug | Who took part | Length | Average weight change | Sponsor |
|---|---|---|---|---|---|
| STEP 1 | Semaglutide (Wegovy injection) | 1,961 adults without diabetes | 68 weeks | -14.9% vs -2.4% | Novo Nordisk |
| STEP 2 | Semaglutide (Wegovy injection) | 1,210 adults with type 2 diabetes | 68 weeks | -9.6% vs -3.4% | Novo Nordisk |
| OASIS 4 | Semaglutide (Wegovy tablets) | 307 adults without diabetes | 64 weeks | -13.6% vs -2.2% | Novo Nordisk |
| SURMOUNT-1 | Tirzepatide (Zepbound) | 2,539 adults without diabetes | 72 weeks | -15.0% to -20.9% vs -3.1% | Eli Lilly |
| SURMOUNT-2 | Tirzepatide | 938 adults with type 2 diabetes | 72 weeks | -12.8% to -14.7% vs -3.2% | Eli Lilly |
| SURMOUNT-5 | Tirzepatide vs semaglutide | 751 adults without diabetes | 72 weeks | -20.2% vs -13.7% | Eli Lilly |
| ATTAIN-1 | Orforglipron (Foundayo) | 3,127 adults without diabetes | 72 weeks | -7.5% to -11.2% vs -2.1% | Eli Lilly |
How much weight can you lose on Zepbound?
Zepbound weight loss data come mainly from the SURMOUNT program. In SURMOUNT-1, published in NEJM in 2022, adults without diabetes lost 15.0%, 19.5% and 20.9% of body weight on average on three strengths over 72 weeks, vs 3.1% on placebo. Between 85% and 91% lost at least 5%, vs 35% on placebo, and half or more of those on the two higher strengths lost at least 20%. Digestive side effects were the most common, mostly mild to moderate and mainly while the strength was being increased.
SURMOUNT-3 (Nature Medicine 2023) enrolled 579 adults who had already lost at least 5% in a 12-week intensive lifestyle program. Over the next 72 weeks they lost a further 18.4% on tirzepatide, while the placebo group regained 2.5%. Counting from the start of the lifestyle phase, the total was about 24% vs 4.5%. The study was funded by Eli Lilly. Zepbound is also approved for moderate to severe obstructive sleep apnea in adults with obesity.
The head-to-head trial: SURMOUNT-5
SURMOUNT-5, published in NEJM in 2025, is the only randomized trial comparing the two leading weekly injections for weight loss. It enrolled 751 adults with obesity but without type 2 diabetes and gave each person the highest strength they could tolerate of either tirzepatide or semaglutide for 72 weeks. Average weight change was -20.2% with tirzepatide and -13.7% with semaglutide, and waist size fell by 18.4 cm vs 13.0 cm. The trial was open-label and funded by Eli Lilly, the maker of tirzepatide. Our semaglutide vs tirzepatide guide covers the two drugs in more depth.
How much weight can you lose on Ozempic?
Ozempic is FDA-approved for type 2 diabetes, not for weight management, so Ozempic weight loss figures come from diabetes trials. In SUSTAIN 1, a 30-week Novo Nordisk trial of 388 adults whose diabetes was managed by diet and exercise, weight fell by 3.7 and 4.5 kg on two semaglutide strengths vs 1.0 kg on placebo. In SUSTAIN 7, a 40-week trial against dulaglutide, it fell by 4.6 and 6.5 kg.
Wegovy contains the same ingredient, semaglutide, and its labeled maintenance strength is higher than Ozempic’s. In STEP 1, adults without diabetes on Wegovy lost 14.9% on average (about 15.3 kg) over 68 weeks. In STEP 2, adults with type 2 diabetes lost 9.6% on Wegovy’s labeled maintenance strength vs 3.4% on placebo, smaller than the 14.9% seen in people without diabetes. Our Wegovy vs Ozempic guide explains the two brands.
Mounjaro weight loss in diabetes trials
Mounjaro and Zepbound both contain tirzepatide. Mounjaro’s August 2026 label approves it for blood sugar control in adults and children 10 and older with type 2 diabetes and for lowering cardiovascular risk in adults with type 2 diabetes, not for weight management. Mounjaro weight loss figures therefore come from diabetes trials. In SURPASS-2, a 40-week Lilly-funded trial of 1,879 adults on metformin, weight fell by 7.6, 9.3 and 11.2 kg on three tirzepatide strengths vs 5.7 kg on semaglutide at its diabetes strength. In SURMOUNT-2, which tested tirzepatide for weight in 938 adults with type 2 diabetes, average loss was 12.8% and 14.7% over 72 weeks vs 3.2% on placebo. See Mounjaro vs Zepbound for how the two labels differ.
Results with daily tablets
Two daily GLP-1 tablets are now approved for weight management. In OASIS 4 (NEJM 2025, funded by Novo Nordisk), 307 adults without diabetes took oral semaglutide or placebo; average weight change at 64 weeks was -13.6% vs -2.2%, and digestive side effects affected 74.0% vs 42.2%. Our Wegovy pill guide covers that tablet. In ATTAIN-1 (NEJM 2025, funded by Eli Lilly), 3,127 adults took orforglipron or placebo for 72 weeks; average change was -7.5% to -11.2% depending on strength vs -2.1%, and 54.6% on the highest strength lost at least 10%. Orforglipron is sold as Foundayo; see our Foundayo guide.
What happens after stopping
Weight usually returns when the drug stops, which is why the labels describe these as long-term medicines. Three trials measured it directly:
- STEP 1 extension (Diabetes, Obesity and Metabolism 2022): 327 participants who had lost 17.3% on semaglutide by week 68 stopped both the drug and the lifestyle program. One year later they had regained 11.6 percentage points, about two-thirds of what they lost, leaving a net loss of 5.6%. Blood pressure and other risk factors moved back toward baseline.
- STEP 4 (JAMA 2021): after a 20-week run-in on semaglutide, people who continued lost a further 7.9% by week 68, while those switched to placebo regained 6.9%.
- SURMOUNT-4 (JAMA 2024): 670 adults lost 20.9% on average during 36 weeks of tirzepatide. Those who continued lost a further 5.5% by week 88; those switched to placebo regained 14.0%.
Why results vary from person to person
Averages hide a wide spread. In STEP 1, 86.4% lost at least 5% of body weight, 69.1% at least 10% and 50.5% at least 15%, which also means about 1 in 7 lost less than 5%. Results depend on reaching and tolerating the higher strengths, having type 2 diabetes, other medicines, and diet and activity. Some participants stopped because of side effects: 4.3% to 7.1% in SURMOUNT-1 vs 2.6% on placebo. Weight loss builds over months rather than weeks; see how long Ozempic takes to work and our guide to eating on GLP-1 medicines.
Fat, muscle and safety
Not all lost weight is fat. The Wegovy and Zepbound labels both state that the drug lowers body weight with greater fat mass loss than lean mass loss, which means some lean tissue, including muscle, is lost too. Digestive effects such as nausea, diarrhea, vomiting and constipation are the most common side effects, and the injectable labels carry a boxed warning about thyroid C-cell tumors in rodents; see GLP-1 side effects. Products sold online as “research” semaglutide or tirzepatide are not FDA-approved; see compounded semaglutide and tirzepatide. Older non-GLP-1 options include Qsymia.
Frequently Asked Questions
How much weight can you lose on Zepbound?
In SURMOUNT-1, adults without diabetes lost 15.0% to 20.9% of body weight on average over 72 weeks, depending on strength, vs 3.1% on placebo. Individual results ranged widely.
How much weight can you lose on Ozempic?
Ozempic is approved for type 2 diabetes, not weight loss. In its diabetes trials, weight fell by about 4 to 6.5 kg over 30 to 40 weeks. Wegovy, the semaglutide brand approved for weight management, averaged 14.9% in STEP 1.
Is Zepbound more effective than Wegovy for weight loss?
In SURMOUNT-5, a 72-week Lilly-funded trial in 751 adults, average weight loss was 20.2% with tirzepatide and 13.7% with semaglutide.
Do people regain weight after stopping GLP-1 drugs?
Usually, yes. In the STEP 1 extension, participants regained about two-thirds of their lost weight within a year of stopping, and in SURMOUNT-4 those switched to placebo regained 14.0%.
Is Mounjaro approved for weight loss?
No. Mounjaro is approved for type 2 diabetes and related cardiovascular risk. The same drug, tirzepatide, is approved for weight management as Zepbound.
Do the GLP-1 pills work as well as the injections?
No trial has compared them directly. Oral semaglutide averaged 13.6% at 64 weeks in OASIS 4, and orforglipron up to 11.2% at 72 weeks in ATTAIN-1.
Peptide Labs does not sell these drugs. This article is general information, not medical advice. Read the Medication Guide that comes with a prescription, and ask a pharmacist or prescriber how this information applies to you.
Last reviewed September 2026.
Related guides: Semaglutide vs Tirzepatide: How the Two Drugs Compare, How Long Does Ozempic Take to Work? Labels and Trials Explained, GLP-1 Side Effects: What Every GLP-1 Drug Label Warns About, Weight Loss Injections: What Is FDA-Approved and What Is Not, Weight Loss Plateau: Why It Happens and What the Evidence Says Helps, Stopping Ozempic: What the Trials Show About Weight Regain, Ozempic Before and After: What the Trial Data Really Show, Zepbound Before and After: Results From the SURMOUNT Trials.