Tirzepatide for Diabetes and Obesity: A Complete Review of the Clinical Trial Evidence | Research

The takeaway

Tirzepatide, the first GLP-1/GIP dual agonist, reduced HbA1c by up to 3% in diabetes and body weight by up to 22.4% in obesity — outperforming every comparator drug tested.

Up to 22.4% weight loss
Tirzepatide 15 mg achieved this body weight reduction over 72 weeks in the SURMOUNT-1 obesity trial — the highest weight loss ever recorded for a medication at the time

What the researchers found

This review synthesizes the entire SURPASS and SURMOUNT-1 clinical trial programs for tirzepatide. In type 2 diabetes (SURPASS), weekly tirzepatide 5-15 mg reduced HbA1c by 1.87-3.02% and body weight by 5.4-12.9 kg over up to 104 weeks, outperforming semaglutide 1 mg, dulaglutide, insulin degludec, and insulin glargine. It also improved liver fat, blood pressure, lipids, and reduced new-onset macroalbuminuria.

In obesity without diabetes (SURMOUNT-1), tirzepatide 5-15 mg produced 16.5-22.4% body weight reduction over 72 weeks — weight loss figures that were unprecedented at the time of publication.

Why it matters

Tirzepatide was the first drug to combine GLP-1 and GIP receptor activation, and the results were transformative — HbA1c reductions of up to 3% and weight loss exceeding 20% represented a step change in what medication alone could achieve for diabetes and obesity.

The numbers in context

HbA1c reduction: 1.87-3.02% · Weight loss (T2DM): 5.4-12.9 kg · Weight loss (obesity): 16.5-22.4% · Up to 104 weeks · Beat semaglutide 1 mg head-to-head

How the study worked

Narrative review summarizing the SURPASS clinical trial program (multiple phase 3 RCTs in type 2 diabetes including head-to-head comparisons with semaglutide, dulaglutide, and insulin) and the SURMOUNT-1 trial (phase 3 RCT in obesity without diabetes). Covers global and Japanese-specific populations.

Who was studied

Review covering adults with type 2 diabetes (SURPASS program) and adults with obesity without diabetes (SURMOUNT-1) from global and Japanese populations

What this study cannot tell us

As a review, this synthesizes existing trial data rather than generating new evidence. Published in early 2023, it covers SURMOUNT-1 but not later SURMOUNT trials or the cardiovascular outcome data. The semaglutide comparison used the 1 mg dose (for diabetes), not the higher 2.4 mg dose used for obesity. Some cardiometabolic benefits are secondary endpoints requiring further confirmatory studies.

How to read the evidence

Rated strong because this review synthesizes data from multiple large phase 3 randomized controlled trials (SURPASS 1-6 and SURMOUNT-1) with active comparators and long treatment durations, representing the highest tier of clinical evidence.

When this study was published

Published in early 2023, this review covers the trial data that led to tirzepatide's approval. Since then, additional SURMOUNT trials and cardiovascular outcome data have been published, but the core SURPASS and SURMOUNT-1 findings reviewed here remain the foundation of tirzepatide's evidence base.

The bigger picture

Tirzepatide's SURPASS and SURMOUNT programs established dual agonism as the new benchmark in metabolic medicine. The results demonstrated that targeting both GLP-1 and GIP receptors produces effects neither could achieve alone, opening the door to triple agonists (like retatrutide) and competing dual agonists (like mazdutide). This review captures the pivotal moment when the field shifted from 'how much can GLP-1 do' to 'what can multi-receptor targeting achieve.'

Questions still open

Does tirzepatide provide cardiovascular outcome benefits similar to or better than semaglutide?
How does the 22.4% weight loss from tirzepatide compare to bariatric surgery outcomes long-term?
Would comparing tirzepatide to semaglutide 2.4 mg (the obesity dose) change the competitive picture?

Common questions

Is tirzepatide better than semaglutide for weight loss?

In the SURPASS-2 head-to-head trial for type 2 diabetes, tirzepatide produced greater HbA1c and weight reductions than semaglutide 1 mg. However, the comparison used semaglutide's diabetes dose, not the higher 2.4 mg obesity dose. Cross-trial comparisons suggest tirzepatide achieves greater weight loss, but a direct head-to-head obesity trial would provide definitive answers.

What are the main side effects of tirzepatide?

The most common side effects are gastrointestinal — nausea, diarrhea, and vomiting — similar to other GLP-1 drugs. These are generally mild to moderate and tend to improve over time. The side effect profile was consistent across the SURPASS and SURMOUNT trials.

Read the original research

Efficacy and Safety of Tirzepatide in Type 2 Diabetes and Obesity Management.

Journal of obesity & metabolic syndrome, 32(1), 25-45

View on PubMed ↗Publisher’s paper ↗

Citation

Sinha, Rachel; Papamargaritis, Dimitris; Sargeant, Jack A; Davies, Melanie J. (2023). Efficacy and Safety of Tirzepatide in Type 2 Diabetes and Obesity Management.. Journal of obesity & metabolic syndrome, 32(1), 25-45. https://doi.org/10.7570/jomes22067