SURMOUNT Trials: Tirzepatide Weight Loss Data

Tirzepatide

22.5% weight loss

The highest dose of tirzepatide produced 22.5% mean body weight reduction versus 2.4% for placebo over 72 weeks in the landmark SURMOUNT-1 trial.

Jastreboff et al., NEJM, 2022

5 trials

in the SURMOUNT program

2,539

participants in SURMOUNT-1

94%

diabetes risk reduction at 3 years

Jastreboff et al., NEJM, 2022

SURMOUNT-1: The Landmark Trial That Changed Everything

SURMOUNT-1 was the pivotal trial that established tirzepatide's weight loss credentials. Published in the New England Journal of Medicine in 2022, it enrolled 2,539 adults with a BMI of 30 or higher (or 27+ with at least one weight-related complication) but without diabetes.^[1]

Participants were randomized 1:1:1:1 to receive once-weekly subcutaneous tirzepatide at 5 mg, 10 mg, or 15 mg, or placebo for 72 weeks. The results at each dose:

At baseline, the mean body weight was 104.8 kg (231 lb) and the mean BMI was 38.0. The 15 mg dose produced 52 pounds of weight loss on average, and more than half of participants at that dose lost over 20% of their body weight. No previous single-agent therapy had achieved these numbers in a phase 3 trial.^[1]

Jastreboff et al. (2022) · N Engl J Med

Population

2,539 adults with BMI 30+ (or 27+ with complications), no diabetes

Intervention

Tirzepatide 5, 10, or 15 mg weekly for 72 weeks

Comparator

Placebo

Finding

15 mg dose produced 20.9% mean weight loss; 57% of participants lost over 20% of body weight

positive Largest weight reduction from any single-agent drug in a phase 3 trial

Jastreboff et al. (2022), New England Journal of Medicine

Beyond weight, SURMOUNT-1 showed improvements across cardiometabolic markers including blood pressure, triglycerides, and waist circumference. Gastrointestinal side effects (nausea, diarrhea, constipation) were the most common adverse events, mostly mild to moderate and concentrated during the 20-week dose-escalation phase. Treatment discontinuation due to adverse events ranged from 4.3% to 7.1% across tirzepatide doses versus 2.6% for placebo.

A body composition sub-analysis published by Look et al. (2025) in Diabetes, Obesity & Metabolism found that on the 15 mg dose, total body weight decreased 21.3%, fat mass decreased 33.9%, and lean mass decreased 10.9%. The ratio was roughly 3:1 fat to lean mass loss, which is better than what bariatric surgery typically achieves but still means substantial muscle loss at higher weight reductions.^[7]

SURMOUNT-2: Tirzepatide in People With Type 2 Diabetes

Weight loss peptide drugs consistently produce smaller reductions in people who also have type 2 diabetes, and SURMOUNT-2 confirmed this pattern for tirzepatide. Published in The Lancet in 2023, the trial enrolled 938 adults with both obesity (BMI 27+) and type 2 diabetes.^[2]

At 72 weeks:

• 10 mg: 13.4% weight loss (vs 3.2% placebo)
• 15 mg: 14.7% weight loss (vs 3.2% placebo)

These numbers are lower than SURMOUNT-1's 19.5% and 20.9% at the same doses, confirming the consistent finding that insulin resistance and metabolic dysfunction blunt weight loss response. Still, 14.7% weight loss in a population with type 2 diabetes exceeded what any previous GLP-1 receptor agonist had achieved in this population.

Without Diabetes (SURMOUNT-1)

• 20.9% weight loss at 15 mg
• 57% lost over 20% body weight
• 52 lbs average loss

With Type 2 Diabetes (SURMOUNT-2)

• 14.7% weight loss at 15 mg
• Lower threshold response
• Still best-in-class for this population

Jastreboff et al., NEJM, 2022; Garvey et al., Lancet, 2023

SURMOUNT-2 also demonstrated substantial glycemic improvements: HbA1c decreased by 2.1 percentage points with tirzepatide 15 mg versus 0.5 points with placebo. Over 80% of participants on tirzepatide achieved an HbA1c below 7.0%, and many reached levels below 5.7% (the threshold for normal glucose tolerance).^[2]

SURMOUNT-3: Adding Tirzepatide After Lifestyle Intervention

SURMOUNT-3 asked a practical clinical question: does tirzepatide add benefit for people who have already lost weight through intensive lifestyle intervention? Published in Nature Medicine in 2023, the trial first put all 579 participants through a 12-week intensive lifestyle program (low-calorie diet plus increased physical activity).^[3]

Participants who achieved at least 5% weight loss during the run-in phase were then randomized to tirzepatide (maximum tolerated dose) or placebo for an additional 72 weeks.

The combined result: participants who received tirzepatide after intensive lifestyle intervention lost a total of 26.6% of their body weight from the original baseline. This was the highest total weight loss number across any SURMOUNT trial, demonstrating that lifestyle intervention and tirzepatide have additive effects.^[3]

This matters for clinical practice because it validates a stepped approach: starting with lifestyle changes, then adding tirzepatide if weight loss goals are not met.

SURMOUNT-4: What Happens When You Stop Tirzepatide

SURMOUNT-4 addressed the question patients care about most after "how much weight will I lose?": what happens when I stop? Published in JAMA in January 2024, the trial had a unique design.^[4]

All 670 participants received open-label tirzepatide (maximum tolerated dose) for 36 weeks. Those who achieved at least 5% weight loss were then randomized to continue tirzepatide or switch to placebo for another 52 weeks.

The results were unambiguous:

• Continue tirzepatide: Additional 5.5% weight loss (25.3% total from baseline)
• Switch to placebo: 14.0% weight regain (9.9% total loss from baseline)

From week 36 to 88, participants who switched to placebo regained an average of 14 percentage points, erasing much of the initial benefit. Those who continued tirzepatide kept losing. The divergence was visible across every metabolic marker: blood pressure, waist circumference, and lipid levels all worsened in the group that stopped treatment.^[4]

SURMOUNT-4 established that tirzepatide works as long as you take it. Stopping treatment leads to predictable and substantial weight regain, matching the pattern seen with semaglutide discontinuation studies. This has implications for insurance coverage, treatment planning, and how obesity is conceptualized: as a chronic condition requiring ongoing management rather than a problem that can be "fixed" with a temporary course of medication. For how this pattern compares to semaglutide, see Semaglutide Weight Regain: What the Studies Show After Discontinuation.

SURMOUNT-5: Tirzepatide vs Semaglutide Head-to-Head

The trial the field had been waiting for. Published in the New England Journal of Medicine in May 2025, SURMOUNT-5 was the first direct head-to-head comparison between tirzepatide (Zepbound) and semaglutide (Wegovy) for obesity.^[5]

The phase 3b, open-label trial randomized 751 adults with obesity (BMI 30+, no diabetes) 1:1 to receive the maximum tolerated dose of either tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) once weekly for 72 weeks.

Results at 72 weeks:

• Tirzepatide: 20.2% weight loss
• Semaglutide: 13.7% weight loss
• Estimated treatment difference: 6.5 percentage points (p<0.001)

Aronne et al. (2025) · N Engl J Med

Population

751 adults with BMI 30+, no diabetes

Intervention

Tirzepatide 10-15 mg weekly for 72 weeks

Comparator

Semaglutide 1.7-2.4 mg weekly for 72 weeks

Finding

Tirzepatide produced 20.2% vs 13.7% weight loss — a 6.5 percentage point advantage over semaglutide

positive Open-label design is a limitation, but the gap is large enough to be clinically meaningful

Aronne et al. (2025), New England Journal of Medicine

Tirzepatide also produced greater reductions in waist circumference (18.4 cm vs 13.0 cm). Gastrointestinal adverse events leading to discontinuation were more common with semaglutide (5.6%) than tirzepatide (2.7%).^[5]

The open-label design is a limitation worth noting. Participants knew which drug they received, which could influence adherence, diet behavior, and subjective reporting of side effects. A double-blind comparison would be more definitive. Still, a 6.5 percentage point gap is large enough that blinding effects are unlikely to explain the entire difference.

For a deeper dive on how these two drugs compare beyond weight loss, see Tirzepatide vs Semaglutide: Which One Leads to More Weight Loss?.

Three-Year Data: Diabetes Prevention

The SURMOUNT-1 extension, published in the New England Journal of Medicine in late 2024, followed participants with both obesity and prediabetes for 176 weeks (3.4 years) of continuous tirzepatide treatment.^[6]

Weight loss was sustained at three years:

• 5 mg: 12.3% weight loss
• 10 mg: 18.7% weight loss
• 15 mg: 19.7% weight loss
• Placebo: 1.3% weight loss

The diabetes prevention finding was remarkable: only 1.3% of tirzepatide-treated participants progressed to type 2 diabetes versus 13.3% on placebo. That translates to a 94% relative risk reduction (hazard ratio 0.07). Even after a 17-week washout period without treatment, the protection persisted: 2.4% of tirzepatide-treated participants versus 13.7% of placebo participants had diabetes.^[6]

94%

reduction in diabetes risk

Only 1.3% of tirzepatide patients developed diabetes vs 13.3% on placebo over 3.4 years

19.7%

weight loss sustained at 3 years

15 mg dose maintained nearly 20% weight reduction over 176 weeks

0.07

hazard ratio for diabetes

One of the strongest diabetes prevention effects ever reported for a single drug

Jastreboff et al., NEJM, 2025

These are stronger diabetes prevention results than those seen with metformin or intensive lifestyle intervention in the landmark Diabetes Prevention Program, though direct comparison across different trials has limitations.

How Tirzepatide Produces These Results

Tirzepatide is a dual GIP/GLP-1 receptor agonist. Unlike semaglutide (which targets GLP-1 receptors only), tirzepatide activates both glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 receptors. The dual mechanism appears to produce effects beyond what GLP-1 alone achieves.

Heise et al. (2023) published data in Diabetes Care showing that tirzepatide reduced appetite, decreased energy intake, and preferentially reduced fat mass in people with type 2 diabetes. Participants on tirzepatide consumed fewer calories without being instructed to diet, and the caloric reduction was sustained over the treatment period.^[8]

The GIP receptor component may explain tirzepatide's advantage over pure GLP-1 agonists. GIP receptors in adipose tissue and the central nervous system appear to enhance fat oxidation and appetite suppression through pathways that are additive to GLP-1 signaling. For a complete breakdown of this dual mechanism, see How Tirzepatide's Dual Mechanism Differs from Single GLP-1 Agonists.

What the SURMOUNT Data Does Not Tell Us

The SURMOUNT program answered the big questions about efficacy and short-term safety. Several gaps remain:

Long-term cardiovascular outcomes. The SELECT trial established semaglutide's cardiovascular benefit. No equivalent outcomes trial has reported for tirzepatide yet. The SURPASS-CVOT trial is ongoing but results are not expected until the late 2020s.

Durability beyond three years. SURMOUNT-1's extension provides 176 weeks of data. Whether weight loss plateaus, continues, or gradually reverses with longer treatment is unknown.

Population specificity. SURMOUNT-1 and SURMOUNT-5 excluded people with diabetes. SURMOUNT-2 included only people with type 2 diabetes. Data on type 1 diabetes, adolescents, and older adults (over 75) is limited.

Real-world adherence. Clinical trial participants receive regular monitoring, dose titration support, and free medication. Real-world adherence, where cost, side effects, and insurance barriers play larger roles, may produce different results.

1. Cell & Lab Studiescompleted

   Receptor binding and signaling pathways well characterized

2. Animal Studiescompleted

   Extensive preclinical data on dual GIP/GLP-1 agonism

3. Small Human Trialscompleted

   Phase 1 and 2 dose-finding studies completed

4. Large Randomized Trialscompleted

   5 phase 3 SURMOUNT trials with thousands of participants, FDA approved

5. Long-Term Outcomes & Meta-Analysiscurrent

   3-year weight and diabetes data available; cardiovascular outcomes trial (SURPASS-CVOT) still ongoing

Tirzepatide has one of the strongest evidence bases of any weight loss medication — five large phase 3 trials, FDA approval, and 3-year follow-up data. The main gap is long-term cardiovascular outcomes, which won't be available until the late 2020s.

Aggregate assessment of SURMOUNT program and ongoing trials

For a practical look at dosing differences and their clinical significance, see Tirzepatide Dose Response: How Weight Loss Changes at Each Dose. For brand name differences, see Mounjaro vs Zepbound: Understanding Tirzepatide's Two Brand Names.

Research Gaps

What would it take?

What questions do the SURMOUNT trials still leave unanswered?

◐

Cardiovascular outcomes trial (does tirzepatide reduce heart attacks and strokes?)

SURPASS-CVOT ongoing, results expected late 2020s

○

Data beyond 3 years of continuous use

Longest follow-up is 176 weeks (3.4 years)

◐

Real-world effectiveness studies (outside clinical trial conditions)

Some early real-world data emerging, but no large published studies

○

Head-to-head comparison with double-blind design

SURMOUNT-5 was open-label; a blinded comparison would be more definitive

○

Data in adolescents, older adults (75+), and type 1 diabetes

Current trials excluded or underrepresented these groups

2 of 5 gaps being actively addressed·Key cardiovascular data likely available by 2028-2029

Based on ClinicalTrials.gov registry and published SURMOUNT program data

The Bottom Line

The SURMOUNT program established tirzepatide as the most effective single-agent weight loss medication tested in phase 3 trials, with 20-22.5% body weight reduction in people without diabetes and 14.7% in people with type 2 diabetes. SURMOUNT-5 demonstrated superiority over semaglutide in a direct comparison. SURMOUNT-4 confirmed that stopping treatment leads to substantial regain. Three-year data showed sustained weight loss and a 94% reduction in diabetes progression. Key unknowns remain: long-term cardiovascular outcomes, durability beyond three years, and real-world performance outside clinical trial conditions.

Frequently Asked Questions

How much weight do you lose on tirzepatide in the SURMOUNT trials?

In SURMOUNT-1, participants without diabetes lost an average of 15.0% (5 mg), 19.5% (10 mg), or 20.9% (15 mg) of their body weight over 72 weeks, compared to 3.1% with placebo (Jastreboff et al., NEJM, 2022). At the highest dose, that translated to approximately 52 pounds of average weight loss. In participants with type 2 diabetes (SURMOUNT-2), results were lower at 13.4% and 14.7% for the 10 mg and 15 mg doses.

Is tirzepatide better than semaglutide for weight loss?

In SURMOUNT-5, the first head-to-head trial, tirzepatide produced 20.2% weight loss versus 13.7% for semaglutide over 72 weeks, a statistically significant difference of 6.5 percentage points (Aronne et al., NEJM, 2025). Tirzepatide also produced greater waist circumference reduction and had lower rates of GI side effects leading to discontinuation (2.7% vs 5.6%). The trial was open-label, which is a limitation.

What happens when you stop taking tirzepatide?

SURMOUNT-4 showed that participants who stopped tirzepatide after 36 weeks regained an average of 14 percentage points of body weight over the following year, compared to continued weight loss of 5.5% in those who stayed on treatment (Aronne et al., JAMA, 2024). Blood pressure, lipids, and waist circumference also worsened after stopping. This pattern matches semaglutide discontinuation data and underscores that these medications manage obesity rather than cure it.

Does tirzepatide prevent type 2 diabetes?

Three-year data from the SURMOUNT-1 extension showed that tirzepatide reduced progression from prediabetes to type 2 diabetes by 94% compared to placebo (1.3% vs 13.3% developed diabetes) over 176 weeks (Jastreboff et al., NEJM, 2025). This protection partially persisted even 17 weeks after stopping treatment. These are the strongest diabetes prevention results reported for any single pharmacological intervention.

What are the side effects of tirzepatide in the SURMOUNT trials?

The most common side effects across all SURMOUNT trials were gastrointestinal: nausea, diarrhea, constipation, and vomiting. Most were mild to moderate in severity and occurred primarily during the initial 20-week dose-escalation period. In SURMOUNT-1, adverse events caused treatment discontinuation in 4.3% to 7.1% of tirzepatide participants versus 2.6% on placebo. Serious adverse events were rare and occurred at similar rates between tirzepatide and placebo groups.

How many SURMOUNT trials are there?

The SURMOUNT program includes five completed trials: SURMOUNT-1 (obesity without diabetes), SURMOUNT-2 (obesity with type 2 diabetes), SURMOUNT-3 (tirzepatide after intensive lifestyle intervention), SURMOUNT-4 (weight maintenance after stopping treatment), and SURMOUNT-5 (head-to-head comparison with semaglutide). A long-term extension of SURMOUNT-1 provided three-year efficacy and diabetes prevention data.

Sources & References

1. 1RPEP-06224·Jastreboff, Ania M et al. (2022). “Tirzepatide Once Weekly for Obesity: Results from the SURMOUNT-1 Trial.” The New England journal of medicine.Study breakdown →PubMed →↩
2. 2RPEP-06898·Garvey, W Timothy et al. (2023). “Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2): a double-blind, randomised, multicentre, placebo-controlled, phase 3 trial..” Lancet (London.Study breakdown →PubMed →↩
3. 3RPEP-07504·Wadden, Thomas A et al. (2023). “Tirzepatide after intensive lifestyle intervention in adults with overweight or obesity: the SURMOUNT-3 phase 3 trial..” Nature medicine.Study breakdown →PubMed →↩
4. 4RPEP-07771·Aronne, Louis J et al. (2024). “What Happens When You Stop Taking Tirzepatide? The SURMOUNT-4 Weight Maintenance Trial.” JAMA.Study breakdown →PubMed →↩
5. 5RPEP-09982·Aronne, Louis J et al. (2025). “Tirzepatide vs Semaglutide for Obesity: The SURMOUNT-5 Head-to-Head Trial.” The New England journal of medicine.Study breakdown →PubMed →↩
6. 6RPEP-11576·Jastreboff, Ania M et al. (2025). “Tirzepatide Cut Type 2 Diabetes Risk by 93% Over 3 Years While Producing Up to 20% Weight Loss.” The New England journal of medicine.Study breakdown →PubMed →↩
7. 7RPEP-12292·Look, Michelle et al. (2025). “What Happens to Fat vs. Muscle When You Lose Weight on Tirzepatide.” Diabetes.Study breakdown →PubMed →↩
8. 8RPEP-06949·Heise, Tim et al. (2023). “Tirzepatide Beats Semaglutide for Fat Loss, but Not Because It Kills Appetite More.” Diabetes care.Study breakdown →PubMed →↩