New England Journal of Medicine June 25, 2021

Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes

Juan P. Frias, Melanie J. Davies, Julio Rosenstock, Federico C. Perez Manghi, Laura Fernandez Lando, Brandon K. Bergman, Bing Liu, Xuewei Cui, Katelyn Brown

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Bottom Line

In patients with type 2 diabetes, once-weekly tirzepatide demonstrated superior reductions in both HbA1c and body weight compared to once-weekly semaglutide over 40 weeks.

Key Findings

1. Mean HbA1c reductions from baseline to 40 weeks were -2.01%, -2.24%, and -2.30% with 5 mg, 10 mg, and 15 mg of tirzepatide, respectively, compared to -1.86% with semaglutide 1 mg [2.1.9].

2. Tirzepatide yielded dose-dependent mean body weight reductions of -7.6 kg, -9.3 kg, and -11.2 kg across the 5 mg, 10 mg, and 15 mg doses, respectively, which were superior to the -5.7 kg reduction observed with semaglutide.

3. Across tirzepatide doses, a significantly greater proportion of patients (up to 46% with 15 mg) achieved an HbA1c of less than 5.7% (normoglycemia) compared to 19% with semaglutide.

4. The safety profile of tirzepatide was consistent with the GLP-1 receptor agonist class, with the most commonly reported adverse events being mild-to-moderate gastrointestinal issues such as nausea, diarrhea, and vomiting.

Study Design

Design

RCT

Open-Label

Sample

1,879

Patients

Duration

40 wk

Median

Setting

Multinational

Population Adults with type 2 diabetes inadequately controlled on metformin therapy alone, with a baseline mean HbA1c of 8.28%, mean age of 56.6 years, and mean weight of 93.7 kg.

Intervention Tirzepatide at a dose of 5 mg, 10 mg, or 15 mg injected subcutaneously once weekly.

Comparator Semaglutide at a dose of 1 mg injected subcutaneously once weekly.

Outcome Mean change in glycated hemoglobin (HbA1c) level from baseline to 40 weeks.

Study Limitations

• The open-label design could introduce bias in subjective reporting of adverse events or lifestyle modifications, although the primary endpoint of HbA1c is objective [1.2.3].

• The 40-week duration is relatively short, preventing the assessment of long-term durability of glycemic control and weight loss.

• The study population lacked broad racial diversity, with only 4.2% of participants identifying as Black, which may restrict the generalizability of the findings.

• The trial was not powered to assess cardiovascular outcomes, which are a critical consideration for newer diabetes therapies.

Clinical Significance

SURPASS-2 established tirzepatide, a first-in-class dual GIP and GLP-1 receptor agonist, as superior to the most potent GLP-1 receptor agonist available at the time (semaglutide 1 mg) for both glycemic control and weight loss. This positioned dual-incretin therapy as a highly efficacious intervention capable of pushing a substantial proportion of patients into normoglycemia and double-digit percentage weight loss without unacceptable hypoglycemia.

Historical Context

The GLP-1 receptor agonist class, led by semaglutide, had previously set a high benchmark in type 2 diabetes management for combined glycemic and weight benefits. Tirzepatide represented a structural evolution by adding GIP agonism (a 'twincretin'). SURPASS-2 was a landmark head-to-head superiority trial that validated this dual-agonism hypothesis, shifting the paradigm of metabolic disease management toward multi-receptor pharmacology and paving the way for tirzepatide's subsequent approval in type 2 diabetes and obesity.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

Tirzepatide is often referred to as a 'twincretin' due to its novel mechanism of action. Based on its receptor targets, how does its dual agonism synergistically improve glycemic control and promote greater weight loss compared to a selective GLP-1 agonist like semaglutide?

Key Response

Tirzepatide activates both GIP and GLP-1 receptors. While GLP-1 slows gastric emptying, promotes satiety, and enhances glucose-dependent insulin secretion, GIP also stimulates insulin secretion and acts directly on adipocytes to improve insulin sensitivity and lipid buffering. Additionally, GIP has glucagonotropic effects during hypoglycemia, providing a nuanced metabolic profile that results in superior efficacy compared to GLP-1 agonism alone.

Resident

Given the robust HbA1c and weight reductions seen in the SURPASS-2 trial, how should the gastrointestinal side effect profile of tirzepatide compared to semaglutide influence your dose titration strategy and patient counseling in a primary care setting?

Key Response

Both medications share a similar dose-dependent gastrointestinal adverse effect profile, primarily nausea, diarrhea, and vomiting. Residents must understand the critical importance of starting at the lowest dose (2.5 mg for tirzepatide) and escalating slowly (every 4 weeks) while counseling patients on dietary modifications (smaller, more frequent meals) to mitigate nausea, improve tolerability, and prevent premature discontinuation of a highly efficacious therapy.

Fellow

While SURPASS-2 demonstrated superior HbA1c and weight reductions over 40 weeks, semaglutide already has established cardiovascular outcome trial (CVOT) data demonstrating MACE reduction (SUSTAIN-6). How should the lack of long-term CVOT data for tirzepatide at the time of this publication influence your medication selection in a diabetic patient with established atherosclerotic cardiovascular disease (ASCVD)?

Key Response

Fellows must balance impressive surrogate endpoints (HbA1c, weight) with hard clinical outcomes (MACE). Guidelines prioritize agents with proven cardiovascular benefit in patients with established ASCVD. Therefore, until the SURPASS-CVOT data is published, a selective GLP-1 RA with proven CV benefit like semaglutide or dulaglutide remains the strictly evidence-based choice for secondary cardiovascular prevention, despite tirzepatide's superior metabolic efficacy.

Attending

In SURPASS-2, nearly half of the patients on the highest tirzepatide dose achieved normoglycemia (HbA1c < 5.7%) and experienced weight loss exceeding 15%. How do these unprecedented findings force a shift in the primary treatment paradigm of Type 2 Diabetes from 'hyperglycemia management' to 'disease remission and obesity treatment'?

Key Response

Attendings should recognize that tirzepatide blurs the lines between traditional diabetes management, medical obesity treatment, and bariatric surgery outcomes. This paradigm shift moves clinical targets away from merely preventing microvascular complications through moderate A1c lowering, toward actively pursuing disease modification, weight-driven metabolic normalization, and potentially long-term diabetes remission.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

SURPASS-2 utilized the 1.0 mg dose of semaglutide as the active comparator. How might the use of a non-maximal dose of semaglutide (given the subsequent approval of the 2.0 mg dose for diabetes) affect the interpretation of the superiority margins, and how does the choice of the 'treatment-policy' versus 'efficacy' estimand impact the generalizability of the trial's results?

Key Response

Critiquing active comparator selection is vital in clinical trial methodology. While 1.0 mg was the maximum approved dose at the trial's inception, the availability of the 2.0 mg dose potentially dampens the clinical magnitude of tirzepatide's superiority. Furthermore, analyzing the 'treatment-policy' estimand (intention-to-treat regardless of adherence or rescue meds) versus the 'efficacy' estimand is critical for distinguishing between real-world pragmatic effectiveness and pure biological efficacy.

Journal Editor

SURPASS-2 was an open-label trial with respect to the specific drug assigned (due to different injection devices), though the specific tirzepatide doses were blinded. As a peer reviewer, how does this lack of double-blinding introduce potential performance and detection bias, particularly regarding patient-reported outcomes like gastrointestinal tolerability and adherence?

Key Response

An open-label design is a significant threat to internal validity. Knowledge of receiving a novel, highly anticipated 'dual-agonist' might create a placebo effect for dietary adherence and weight loss behaviors. It can also influence how patients report subjective adverse events like nausea, potentially skewing tolerability data, dropout rates, and the ultimate safety profile comparison between the two arms.

Guideline Committee

Current ADA/EASD consensus guidelines recommend GLP-1 RAs with proven CV benefit as first-line or early therapy for patients with high cardiovascular risk, and highly prioritize weight management. Based on SURPASS-2's superior weight and A1c outcomes but pending long-term MACE data, where exactly should dual GIP/GLP-1 receptor agonists be positioned in the updated treatment algorithms compared to established GLP-1 RAs?

Key Response

The committee must weigh unprecedented surrogate marker efficacy against the gold-standard of hard MACE data. Tirzepatide should be positioned at the very top of the 'compelling need to minimize weight gain or promote weight loss' pathway due to SURPASS-2 findings. However, established GLP-1 RAs with proven CV benefit must remain prioritized in the ASCVD/CKD specific pathways until tirzepatide's dedicated cardiovascular outcome trials (e.g., SURPASS-CVOT) definitively prove non-inferiority or superiority for major adverse cardiovascular events.

Clinical Landscape

Noteworthy Related Trials

2016

SUSTAIN-6 Trial

n = 3,297 · NEJM

Tested

Semaglutide 0.5mg or 1.0mg weekly

Population

T2DM patients with high cardiovascular risk

Comparator

Placebo

Endpoint

3-point MACE

Key result: Semaglutide significantly reduced the risk of major adverse cardiovascular events compared to placebo.

2018

SUSTAIN-7 Trial

n = 1,201 · Lancet Diabetes Endocrinol

Tested

Semaglutide 0.5mg or 1.0mg weekly

Population

T2DM patients inadequately controlled on metformin

Comparator

Dulaglutide 0.75mg or 1.5mg weekly

Endpoint

Change in HbA1c from baseline to week 40

Key result: Semaglutide was superior to dulaglutide in improving glycemic control and reducing body weight.

2021

SURPASS-1 Trial

n = 478 · Lancet

Tested

Tirzepatide 5mg, 10mg, or 15mg weekly

Population

T2DM patients inadequately controlled by diet and exercise

Comparator

Placebo

Endpoint

Change in HbA1c from baseline to 40 weeks

Key result: Tirzepatide provided robust, clinically meaningful improvements in HbA1c and body weight compared to placebo.

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