What is the SURMOUNT-2 trial?

SURMOUNT-2 is a phase 3, randomized, double-blind, placebo-controlled trial that tested two doses of tirzepatide (10 mg and 15 mg, injected weekly) against placebo for weight management in 938 adults with both type 2 diabetes and a BMI of 27 or higher. The study ran for 72 weeks and was published in *The Lancet* in June 2023.

How much weight did participants lose in SURMOUNT-2?

On the efficacy estimand (which models what would happen if everyone stayed on treatment), the 15 mg group lost an average of 15.7% of body weight, and the 10 mg group lost 13.4%. The placebo group lost 3.3%. Under the more conservative treatment-policy estimand, the numbers were 14.7%, 12.8%, and 3.2%, respectively.

How does SURMOUNT-2 differ from SURMOUNT-1?

SURMOUNT-1 enrolled adults with obesity but without type 2 diabetes. SURMOUNT-2 specifically recruited people with both obesity and type 2 diabetes. Weight loss in SURMOUNT-2 was slightly lower (about 15.7% vs. 20.9% at 15 mg), which is expected because diabetes makes pharmacological weight loss harder.

Is tirzepatide better than semaglutide for weight loss in type 2 diabetes?

SURMOUNT-2 did not compare tirzepatide to semaglutide directly. The STEP-2 trial of semaglutide 2.4 mg in a similar population showed roughly 6.2% weight loss at 68 weeks. Cross-trial comparisons suggest tirzepatide produces larger reductions, but a head-to-head trial is needed for a definitive answer.

What were the main side effects in SURMOUNT-2?

Gastrointestinal symptoms were the most common side effects. Nausea affected about 25%, 27% of tirzepatide-treated participants (vs. 8% on placebo), diarrhea about 17%, 21%, and vomiting about 11%, 13%. Most of these events were mild to moderate and occurred during the dose-escalation phase.

Did SURMOUNT-2 participants also see improvements in blood sugar?

Yes. HbA1c dropped by an average of 2.1 percentage points in both tirzepatide groups compared with 0.5 points on placebo. More than 80% of participants on tirzepatide 15 mg reached an HbA1c below 7.0%, and roughly half reached below 5.7%.

Who was excluded from SURMOUNT-2?

The trial excluded patients on insulin, sulfonylureas, or more than two oral diabetes medications. It also excluded people with a history of pancreatitis, medullary thyroid carcinoma, MEN2, or prior bariatric surgery. This means the results apply most directly to patients whose diabetes is managed with metformin and/or an SGLT2 inhibitor.

Does weight come back after stopping tirzepatide?

SURMOUNT-2 did not study post-treatment weight regain. Data from related GLP-1 class trials, such as the STEP-1 extension study, show that a majority of lost weight returns within one year of stopping treatment. Until a tirzepatide-specific discontinuation study is published, clinicians should assume a similar pattern.

What doses of tirzepatide were tested in SURMOUNT-2?

Two maintenance doses were tested: 10 mg and 15 mg, both given as once-weekly subcutaneous injections. Both groups started at 2.5 mg and escalated by 2.5 mg every four weeks. The 10 mg group reached maintenance at week 12; the 15 mg group at week 20.

Is tirzepatide FDA-approved based on SURMOUNT-2?

Tirzepatide is FDA-approved as Mounjaro for type 2 diabetes and as Zepbound for chronic weight management in adults with obesity or overweight with at least one weight-related comorbidity. SURMOUNT-2 was one of several trials supporting these approvals.

SURMOUNT-2 Trial: A Plain-English Overview of What It Established

By HealthRX.com Medical Team

Published May 25, 2026Updated May 25, 2026Last reviewed May 25, 2026

Clinical image for SURMOUNT-2 Trial: A Plain-English Overview of What It Established Image: HealthRX.com clinical image

At a glance

| Detail | Value | |---|---| | Trial name | SURMOUNT-2 (NCT04657003) | | N | 938 randomized | | Population | Adults with BMI ≥27 kg/m² and type 2 diabetes (HbA1c 7.0%, 10.0%) | | Intervention | Tirzepatide 10 mg or 15 mg subcutaneous injection, once weekly | | Comparator | Matched placebo, once weekly | | Duration | 72 weeks (including 20-week dose escalation) | | Primary endpoint | Percentage change in body weight from baseline at week 72 | | Key result | −12.8% (10 mg) and −14.7% (15 mg) vs −3.2% (placebo); treatment-policy estimand. Efficacy estimand: −13.4% (10 mg), −15.7% (15 mg) vs −3.3% placebo | | Published | The Lancet, June 2023 |

The question SURMOUNT-2 was designed to answer

Weight loss trials in people without diabetes (SURMOUNT-1, for example) tend to produce larger numbers on the scale. Type 2 diabetes makes pharmacological weight reduction harder. Insulin resistance, compensatory hunger signaling, and the glucose-lowering medications patients already take (some of which cause weight gain) all blunt the effect. The clinical question behind SURMOUNT-2 was specific: can tirzepatide still produce clinically meaningful weight loss in adults whose type 2 diabetes complicates the picture?

Prior GLP-1 receptor agonists like semaglutide 2.4 mg had shown weight reductions in the range of 6%, 7% in people with type 2 diabetes (STEP-2 trial). Tirzepatide is not a pure GLP-1 agonist. It also activates the glucose-dependent insulinotropic polypeptide (GIP) receptor, a second incretin pathway. The hypothesis was that this dual mechanism could push weight loss higher, even in a metabolically resistant population.

Who was enrolled, and who was not

The SURMOUNT-2 investigators recruited 938 adults across 77 sites in seven countries (Argentina, Brazil, India, Israel, Japan, Russia, and the United States). Participants needed a BMI of 27 kg/m² or higher and a confirmed diagnosis of type 2 diabetes with an HbA1c between 7.0% and 10.0%.

Permitted background therapy included metformin alone, a single SGLT2 inhibitor alone, or the combination of metformin plus an SGLT2 inhibitor. Patients already on insulin, other injectable glucose-lowering drugs, or more than two oral diabetes medications were excluded. So were individuals with a history of pancreatitis, medullary thyroid carcinoma, or multiple endocrine neoplasia syndrome type 2 (MEN2), consistent with the class-wide precautions listed in the tirzepatide prescribing information.

Key baseline characteristics:

| Characteristic | Tirzepatide 10 mg (n=312) | Tirzepatide 15 mg (n=311) | Placebo (n=315) | |---|---|---|---| | Mean age (years) | 54.2 | 53.9 | 54.5 | | Mean body weight (kg) | 100.7 | 101.7 | 100.7 | | Mean BMI (kg/m²) | 36.1 | 36.0 | 36.1 | | Mean HbA1c (%) | 8.02 | 7.96 | 8.03 | | Mean diabetes duration (years) | 8.3 | 8.8 | 8.1 | | Metformin use (%) | ~92 | ~92 | ~92 |

This was a population with established disease, not early-stage diabetes caught incidentally on a screening lab.

How the trial was run

Participants were randomized 1:1:1 to tirzepatide 10 mg, tirzepatide 15 mg, or placebo. All three groups followed the same dose-escalation schedule: starting at 2.5 mg weekly, increasing by 2.5 mg every four weeks until the assigned maintenance dose was reached. The escalation period lasted 20 weeks for the 15 mg group and 12 weeks for the 10 mg group.

Every participant received lifestyle counseling targeting a 500 kcal/day deficit and at least 150 minutes per week of physical activity. This is standard in obesity trials and ensures the comparator arm is not simply "nothing."

Two statistical approaches were pre-specified for analyzing the primary endpoint. The first, called the treatment-policy estimand, includes all randomized participants regardless of whether they completed treatment or adhered to the protocol. If someone dropped out, their last available data was used. This gives the most conservative, real-world picture. The second, called the efficacy estimand, estimates the treatment effect assuming all participants stayed on their assigned dose for the full 72 weeks. It uses a statistical model to handle missing data from discontinuations. Both estimands were co-primary.

What SURMOUNT-2 found

Weight loss

The headline numbers, reported in The Lancet, were striking for a type 2 diabetes population:

| Outcome (week 72) | Tirzepatide 10 mg | Tirzepatide 15 mg | Placebo | |---|---|---|---| | Weight change, treatment-policy estimand | −12.8% | −14.7% | −3.2% | | Weight change, efficacy estimand | −13.4% | −15.7% | −3.3% | | Absolute weight loss (treatment-policy) | −12.9 kg | −14.7 kg | −3.2 kg | | ≥5% weight loss (treatment-policy) | 79.2% | 82.8% | 32.5% | | ≥10% weight loss (treatment-policy) | 57.1% | 66.1% | 10.5% | | ≥15% weight loss (treatment-policy) | 34.3% | 47.4% | 2.9% |

The difference from placebo was statistically significant at both doses (p<0.0001 for all comparisons). For context, this 14.7% to 15.7% range in a type 2 diabetes cohort approaches what SURMOUNT-1 achieved in people without diabetes (roughly 20% at 15 mg), which was previously considered an unreachable benchmark in patients carrying the metabolic burden of diabetes.

Glycemic control

Although HbA1c change was a secondary endpoint, the results were large. Mean HbA1c dropped by 2.1 percentage points in the 10 mg group and 2.1 points in the 15 mg group, compared with 0.5 points in the placebo group. More than 80% of participants on tirzepatide 15 mg reached an HbA1c below 7.0%, and roughly 50% reached below 5.7%, which is the threshold the American Diabetes Association uses to define normal glucose tolerance.

Cardiometabolic markers

Improvements extended beyond weight and glucose. Tirzepatide groups showed reductions in waist circumference (approximately 10 cm at 15 mg), fasting insulin, triglycerides, and systolic blood pressure. These secondary findings are consistent with the broader metabolic improvements seen across the SURMOUNT program.

Safety: what the trial reported honestly

Gastrointestinal side effects dominated the adverse event profile, as they do across the GLP-1 and dual-agonist class. Nausea, diarrhea, and vomiting were the most commonly reported treatment-emergent events, and most occurred during the dose-escalation phase.

| Adverse event | Tirzepatide 10 mg | Tirzepatide 15 mg | Placebo | |---|---|---|---| | Any GI event | 53.5% | 55.9% | 26.3% | | Nausea | 24.7% | 27.0% | 8.3% | | Diarrhea | 21.2% | 17.4% | 8.3% | | Vomiting | 10.6% | 13.2% | 2.2% | | Discontinuation due to AE | 4.8% | 7.4% | 2.5% |

Serious adverse events occurred in 5.4% (10 mg), 4.5% (15 mg), and 4.1% (placebo). The trial reported no cases of pancreatitis in the tirzepatide groups and no medullary thyroid carcinoma. Hypoglycemia was uncommon (roughly 1%, 3% across groups), since the excluded medications (insulin, sulfonylureas) are the ones that typically drive hypoglycemic risk.

Gallbladder-related events (cholelithiasis, cholecystitis) occurred in a small number of tirzepatide-treated participants, a known class association with rapid weight loss. The FDA label for tirzepatide carries warnings about gallbladder events for this reason.

Limitations the authors acknowledged

The investigators were transparent about several constraints that affect how far these data can be generalized:

Restricted background therapy. By excluding patients on insulin or sulfonylureas, the trial enrolled people whose diabetes was manageable on simpler regimens. Patients with more advanced disease, longer insulin dependence, or triple oral therapy may not respond identically.
72-week duration. The trial provides no data on what happens after treatment stops. Weight regain after discontinuation of GLP-1 class drugs is well documented in studies like STEP-1 extension, and there is no reason to assume tirzepatide is exempt from this pattern.
Geographic and demographic composition. Approximately 62% of participants were White, 5% were Black, and the trial included sites in countries with different dietary and lifestyle baselines than the United States. Racial and ethnic diversity was limited.
No active comparator. SURMOUNT-2 compared tirzepatide to placebo, not to semaglutide or another GLP-1 agonist. Cross-trial comparisons with STEP-2 are tempting but unreliable because of differences in patient populations, baseline HbA1c, and permitted background therapy.
Exclusion of prior bariatric surgery. People with a history of weight-loss surgery were not eligible, so the data do not speak to whether tirzepatide adds benefit in that population.

What SURMOUNT-2 means for clinical practice

Before SURMOUNT-2, clinicians treating patients with both obesity and type 2 diabetes had to choose between optimizing glucose and optimizing weight, often with different drugs. Tirzepatide collapses that tradeoff. A single weekly injection produced HbA1c reductions competitive with the best glucose-lowering agents on the market while simultaneously driving weight loss previously seen only in non-diabetic populations.

The American Diabetes Association's 2024 Standards of Care now lists GLP-1 and dual GIP/GLP-1 receptor agonists as preferred second-line agents for patients with type 2 diabetes and obesity, a recommendation supported in part by SURMOUNT-2 data.

Practical barriers remain. Cost and insurance coverage for tirzepatide (branded as Mounjaro for diabetes and Zepbound for obesity) continue to limit access. Supply constraints have affected availability in the United States intermittently since launch. And the question of long-term durability, specifically what happens to weight and glycemic control when the drug is stopped, remains unanswered by this trial alone.

Still, the data are clear on what 72 weeks of treatment can achieve: roughly 15% weight loss and near-normalization of blood sugar in a population that historically responds poorly to weight interventions.

Frequently asked questions

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References

Garvey WT, Frias JP, Jastreboff AM, et al. 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. The Lancet. 2023;402(10402):613-626. PubMed
Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205-216. PubMed (SURMOUNT-1)
Davies M, Færch L, Jeppesen OK, et al. Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2): a randomised, double-blind, double-dummy, placebo-controlled, phase 3 trial. The Lancet. 2021;397(10278):971-984. PubMed
U.S. Food and Drug Administration. Mounjaro (tirzepatide) prescribing information. FDA Label
American Diabetes Association Professional Practice Committee. 9. Pharmacologic approaches to glycemic treatment: Standards of Care in Diabetes, 2024. Diabetes Care. 2024;47(Suppl 1):S145-S157. Diabetes Care
Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide. Diabetes Obes Metab. 2022;24(8):1553-1564. PubMed