GLP-1 Evidence

Drug

Tirzepatide: what the trials show

Tirzepatide produced the largest mean weight losses ever recorded for a drug in a randomised obesity trial. It is also the one with the most interesting non-weight results.

Updated 3 min read 30 citations Evidence strength 5/5

Shopfront of a German pharmacy seen from the street
muckelfloh · CC BY 3.0 · Wikimedia Commons

SURMOUNT-1: the largest effect size in the field

SURMOUNT-1 randomised adults with obesity and without diabetes to tirzepatide 5, 10 or 15 mg weekly, or placebo, for 72 weeks [8]. Mean weight change at the top dose was about −20.9%, with the 5 mg dose already around −15% — meaning the lowest tirzepatide dose roughly matched the best semaglutide result. More than half of participants at the higher doses lost at least 20% of body weight.

A continuation of that programme extended follow-up and reported on diabetes prevention alongside sustained weight reduction [5], which matters because it moves the endpoint from a number on a scale to a clinical event.

Weight loss efficacy

The diabetes penalty applies here too

SURMOUNT-2 ran the same protocol in adults with obesity and type 2 diabetes and found roughly 14.7% mean weight loss at the top dose [7]. Again: a large effect, and again noticeably smaller than in the non-diabetic population. Meta-analysis comparing the two drugs in type 2 diabetes puts the relative ordering on firmer ground [1][3].

Tirzepatide — mean weight change by trial and population
TrialPopulationDoseDurationMean weight change
SURMOUNT-1 [8]Obesity, no diabetes15 mg72 weeks≈ −20.9%
SURMOUNT-1 [8]Obesity, no diabetes5 mg72 weeks≈ −15%
SURMOUNT-2 [7]Obesity + type 2 diabetes15 mg72 weeks≈ −14.7%
SURMOUNT-5 [10]Obesity, head-to-head vs semaglutide≤15 mg72 weeksSuperior to semaglutide

Beating semaglutide directly

Indirect comparisons and real-world cohorts had pointed this way for a while [12], but the trial that settled it compared the two drugs head-to-head at obesity doses in the same population, and tirzepatide won on mean weight loss by a substantial margin [10]. In type 2 diabetes, SURPASS-2 had already shown superiority over semaglutide 1 mg on both glycaemic and weight endpoints [9].

The results that are not about weight

Two dedicated trials moved tirzepatide beyond obesity as a category.

  • Obstructive sleep apnoea. In adults with moderate-to-severe OSA and obesity, tirzepatide reduced the apnoea-hypopnoea index substantially against placebo [6]. This is the first pharmacological treatment with randomised evidence in a condition previously managed almost entirely with CPAP.
  • Heart failure with preserved ejection fraction. In HFpEF with obesity — a phenotype with very few effective treatments — tirzepatide improved outcomes against placebo [4].
  • Cardiovascular events. A dedicated comparison against dulaglutide reported cardiovascular outcomes in type 2 diabetes [11], adding to the earlier pre-specified meta-analysis that found no signal of cardiovascular harm.

It also appears in the European guidance on steatotic liver disease alongside semaglutide [2].

Common questions

Is Mounjaro the same as Zepbound?
Same molecule, different brand names for the diabetes and obesity indications respectively.
Is tirzepatide simply better than semaglutide?
On mean weight loss in a head-to-head obesity trial, yes [10]. On everything else — tolerability for a given person, cost, availability, and the specific comorbidity you are treating — the answer is individual. Semaglutide has the larger cardiovascular outcome dataset.
Does the GIP component cause the extra weight loss?
It is the obvious candidate, but the mechanism is genuinely unresolved. Blocking GIP also produces weight loss in some models, which is one of the odder open problems in the field.
Do I have to reach 15 mg?
No. The 5 mg dose produced around 15% mean loss in SURMOUNT-1 [8], comparable to the best semaglutide result. Dose is titrated against tolerability.
Made-up bed in a three-person internal medicine ward room
玄史生 · CC0 · Wikimedia Commons
The evidence behind this page A stacked bar showing the composition of the 30 publications cited on this page by study type. 6203meta-analysis (6)randomised trial (20)review (1)other (3)
30 publications, 2018–2025. That is a mix with both trials and syntheses in it, which is the position from which a claim about cause is reasonable. Source: this page’s own citation list, below.

References

Every citation below links to the original peer-reviewed record on PubMed or via DOI. Nothing here is a substitute for medical advice.

  1. Efficacy and Safety of Glucagon-Like Peptide-1 Receptor Agonists for Weight Loss Among Adults Without Diabetes : A Systematic Review of Randomized Controlled Trials Moiz A, Filion KB, Toutounchi H, et al. · Annals of internal medicine · 2025 · Systematic review DOIPubMed 39761578
  2. Subcutaneously administered tirzepatide vs semaglutide for adults with type 2 diabetes: a systematic review and network meta-analysis of randomised controlled trials Karagiannis T, Malandris K, Avgerinos I, et al. · Diabetologia · 2024 · Meta-analysis DOIPubMed 38613667Full text
  3. EASL-EASD-EASO Clinical Practice Guidelines on the management of metabolic dysfunction-associated steatotic liver disease (MASLD): Executive Summary Diabetologia · 2024 · Clinical guideline DOIPubMed 38869512Full text
  4. EASL-EASD-EASO Clinical Practice Guidelines on the management of metabolic dysfunction-associated steatotic liver disease (MASLD) Journal of hepatology · 2024 · Clinical guideline DOIPubMed 38851997
  5. Comparative effectiveness of GLP-1 receptor agonists on glycaemic control, body weight, and lipid profile for type 2 diabetes: systematic review and network meta-analysis Yao H, Zhang A, Li D, et al. · BMJ (Clinical research ed.) · 2024 · Meta-analysis DOIPubMed 38286487Full text
  6. Risk of major adverse cardiovascular events and stroke associated with treatment with GLP-1 or the dual GIP/GLP-1 receptor agonist tirzepatide for type 2 diabetes: A systematic review and meta-analysis Stefanou MI, Theodorou A, Malhotra K, et al. · European stroke journal · 2024 · Meta-analysis DOIPubMed 38400569Full text
  7. Tirzepatide did not impact metabolic adaptation in people with obesity, but increased fat oxidation Ravussin E, Sanchez-Delgado G, Martin CK, et al. · Cell metabolism · 2025 · Randomised controlled trial DOIPubMed 40203836
  8. Efficacy and safety of tirzepatide in children and adolescents with type 2 diabetes (SURPASS-PEDS): a randomised, double-blind, placebo-controlled, phase 3 trial Hannon TS, Chao LC, Barrientos-Pérez M, et al. · Lancet (London, England) · 2025 · Randomised controlled trial DOIPubMed 40975112
  9. Efficacy and safety of once-weekly tirzepatide in Japanese patients with obesity disease (SURMOUNT-J): a multicentre, randomised, double-blind, placebo-controlled phase 3 trial Kadowaki T, Kiyosue A, Shingaki T, et al. · The lancet. Diabetes & endocrinology · 2025 · Randomised controlled trial DOIPubMed 40031941
  10. Tirzepatide and muscle composition changes in people with type 2 diabetes (SURPASS-3 MRI): a post-hoc analysis of a randomised, open-label, parallel-group, phase 3 trial Sattar N, Neeland IJ, Dahlqvist Leinhard O, et al. · The lancet. Diabetes & endocrinology · 2025 · Randomised controlled trial DOIPubMed 40318682
  11. Tirzepatide for Heart Failure with Preserved Ejection Fraction and Obesity Packer M, Zile MR, Kramer CM, et al. · The New England journal of medicine · 2025 · Randomised controlled trial DOIPubMed 39555826
  12. Tirzepatide for Obesity Treatment and Diabetes Prevention Jastreboff AM, le Roux CW, Stefanski A, et al. · The New England journal of medicine · 2025 · Randomised controlled trial DOIPubMed 39536238
  13. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight Look M, Dunn JP, Kushner RF, et al. · Diabetes, obesity & metabolism · 2025 · Randomised controlled trial DOIPubMed 39996356Full text
  14. Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical Trial Aronne LJ, Sattar N, Horn DB, et al. · JAMA · 2024 · Randomised controlled trial DOIPubMed 38078870Full text
  15. Tirzepatide for Weight Reduction in Chinese Adults With Obesity: The SURMOUNT-CN Randomized Clinical Trial Zhao L, Cheng Z, Lu Y, et al. · JAMA · 2024 · Randomised controlled trial DOIPubMed 38819983Full text
  16. Tirzepatide for the Treatment of Obstructive Sleep Apnea and Obesity Malhotra A, Grunstein RR, Fietze I, et al. · The New England journal of medicine · 2024 · Randomised controlled trial DOIPubMed 38912654Full text
  17. Tirzepatide vs Insulin Lispro Added to Basal Insulin in Type 2 Diabetes: The SURPASS-6 Randomized Clinical Trial Rosenstock J, Frías JP, Rodbard HW, et al. · JAMA · 2023 · Randomised controlled trial DOIPubMed 37786396Full text
  18. 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 Garvey WT, Frias JP, Jastreboff AM, et al. · Lancet (London, England) · 2023 · Randomised controlled trial DOIPubMed 37385275
  19. Tirzepatide Reduces Appetite, Energy Intake, and Fat Mass in People With Type 2 Diabetes Heise T, DeVries JH, Urva S, et al. · Diabetes care · 2023 · Randomised controlled trial DOIPubMed 36857477Full text
  20. Effect of Subcutaneous Tirzepatide vs Placebo Added to Titrated Insulin Glargine on Glycemic Control in Patients With Type 2 Diabetes: The SURPASS-5 Randomized Clinical Trial Dahl D, Onishi Y, Norwood P, et al. · JAMA · 2022 · Randomised controlled trial DOIPubMed 35133415Full text
  21. Tirzepatide Once Weekly for the Treatment of Obesity Jastreboff AM, Aronne LJ, Ahmad NN, et al. · The New England journal of medicine · 2022 · Randomised controlled trial DOIPubMed 35658024
  22. Efficacy and safety of a novel dual GIP and GLP-1 receptor agonist tirzepatide in patients with type 2 diabetes (SURPASS-1): a double-blind, randomised, phase 3 trial Rosenstock J, Wysham C, Frías JP, et al. · Lancet (London, England) · 2021 · Randomised controlled trial DOIPubMed 34186022
  23. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes Frías JP, Davies MJ, Rosenstock J, et al. · The New England journal of medicine · 2021 · Randomised controlled trial DOIPubMed 34170647
  24. LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus: From discovery to clinical proof of concept Coskun T, Sloop KW, Loghin C, et al. · Molecular metabolism · 2018 · Randomised controlled trial DOIPubMed 30473097Full text
  25. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity Aronne LJ, Horn DB, le Roux CW, et al. · The New England journal of medicine · 2025 · Clinical trial DOIPubMed 40353578
  26. Cardiovascular Outcomes with Tirzepatide versus Dulaglutide in Type 2 Diabetes Nicholls SJ, Pavo I, Bhatt DL, et al. · The New England journal of medicine · 2025 · Clinical trial DOIPubMed 41406444
  27. Tirzepatide, a dual GIP/GLP-1 receptor co-agonist for the treatment of type 2 diabetes with unmatched effectiveness regrading glycaemic control and body weight reduction Nauck MA, D'Alessio DA · Cardiovascular diabetology · 2022 · Review DOIPubMed 36050763Full text
  28. Semaglutide and Tirzepatide in Patients With Heart Failure With Preserved Ejection Fraction Krüger N, Schneeweiss S, Fuse K, et al. · JAMA · 2025 · Journal article DOIPubMed 40886075Full text
  29. Semaglutide vs Tirzepatide for Weight Loss in Adults With Overweight or Obesity Rodriguez PJ, Goodwin Cartwright BM, Gratzl S, et al. · JAMA internal medicine · 2024 · Journal article DOIPubMed 38976257Full text
  30. New Drug: Tirzepatide (Mounjaro(™)) Gettman L · The Senior care pharmacist · 2023 · Journal article DOIPubMed 36751934