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Tirzepatide and Retatrutide Together: What Is Known

Tirzepatide and Retatrutide taken together: what each one is, how each is regulated, and what is known about combining them.

Medically reviewed by Juan Pablo Frías, MD · · DisclosureUpdated
GLP-1 / GIP dual agonistFDA approved (Mounjaro, Zepbound)TirzepatideFDA-approved dual GIP and GLP-1 receptor agonist; in a large trial, mean weight change at week 72 was -15.0% on 5-mg and -19.5% on 10-mg weekly doses.[15]GLP-1 & metabolicGLP-1 / GIP / glucagon triple agonistInvestigational · phase 3RetatrutideInvestigational triple GIP, GLP-1 and glucagon receptor agonist, not FDA-approved; a phase 3 TRIUMPH trial reported mean weight change of -25.0% at the 12-mg dose versus -3.9% with placebo.[1]GLP-1 & metabolic
Interaction notes

Timing, interactions and safety

Evidence for the combination

No studies tested these together (PubMed search: 108 results, 2 Oct 2026).

Retatrutide is not FDA approved, and we have no sourced data on combining it with Tirzepatide.
Each component

Side by side

Showing 9 of 13 fields where the two differ. Category, PCAC vote, Jul 2026, Evidence strength, Named in FDA warning letters, 2026 are the same or both unknown.

FieldTirzepatideRetatrutide
ClassGLP-1 / GIP dual agonistGLP-1 / GIP / glucagon triple agonist
Also calledtirz, tirze, Mounjaro, Zepboundreta, GLP-3, LY3437943
FDA statusFDA approved (Mounjaro, Zepbound)Investigational · phase 3
WADANot on the WADA Prohibited ListGLP-1 and GIP agonists are not named anywhere on the 2026 list. This one is an approved medicine, so the catch-all S0 (which only covers drugs with no approval anywhere) does not apply to it.Prohibited by WADA (S0)Retatrutide is not named, and GLP-1/amylin class agonists are not listed. But it is an investigational drug with no approval in the sources we reviewed, and S0 prohibits drugs under clinical development that no authority has approved. If it is approved somewhere this would change.
Half-lifeapproximately 5 dayssubcutaneous · FDA label (Mounjaro)approximately 6 dayssubcutaneous · Lancet 2022, PMID 36354040
Human studies we summarised24 human (22 randomized or controlled) of 30 summarised11 human (11 randomized or controlled) of 16 summarised
Typical study doses
Vial sizes sold5 mg, 10 mg, 15 mg, 20 mg, 30 mg, 40 mg, 50 mg, 60 mg, 120 mg5 mg, 10 mg, 12 mg, 15 mg, 20 mg, 24 mg, 30 mg, 36 mg, 40 mg, 50 mg, 60 mg
US searches per month1,220,000 · +30% searches823,000 · +172% searches
Related tools

Tirzepatide vs Retatrutide

Choosing between the two rather than combining them? The comparison lines them up field by field.

Open the comparison
ComparisonTirzepatide vs Retatrutide

What people search

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US monthly searches, Google Keyword Planner, Oct 2026. Shown so you can see which questions this page answers.

Sources

  1. 1Retatrutide phase 3 TRIUMPH-1 results publishedNEJM (PubMed 42814954) · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  2. 2FDA warning letters to five research-peptide sellersFDA warning letter (NuScience Peptides; 1 of 5) · 2026fda.govAccessed 2 Oct 2026
  3. 3Eli Lilly sues six retatrutide sellersEli Lilly (press release) · 2026investor.lilly.comAccessed 2 Oct 2026
  4. 4FDA proposes excluding semaglutide, tirzepatide and liraglutide from the 503B bulks listFDA · 2026fda.govAccessed 2 Oct 2026
  5. 5Seven FDA warning letters to online sellers of GLP-1 productsFDA warning letter (Gram Peptides; 1 of 7) · 2026fda.govAccessed 2 Oct 2026
  6. 6World Anti-Doping Code International Standard Prohibited List 2026World Anti-Doping Agency · 2026wada-ama.orgAccessed 2 Oct 2026
  7. 7These highlights do not include all the information needed to use MOUNJARO safely and effectively. See full prescribing information for MOUNJARO. MOUNJARO ® (tirzepatide) Injection, for subcutaneous uFDA label (Mounjaro), DailyMed · current labeldailymed.nlm.nih.govAccessed 2 Oct 2026
  8. 8Ixekizumab With Tirzepatide Achieved Greater Disease Control Than Ixekizumab Alone in Adults With Psoriatic Arthritis and Overweight or Obesity: Results From a Randomized Clinical Trial.Arthritis & rheumatology (Hoboken, N.J.) · 2026PMID 41903163Accessed 2 Oct 2026
  9. 9Psychiatric Safety of Tirzepatide in People With Obesity and No Known Major Psychopathology: A Post Hoc Analysis of SURMOUNT.Obesity (Silver Spring, Md.) · 2026PMID 41537305Accessed 2 Oct 2026
  10. 10Tirzepatide as Compared with Semaglutide for the Treatment of Obesity.The New England journal of medicine · 2025PMID 40353578Accessed 2 Oct 2026
  11. 11LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial.Lancet (London, England) · 2022PMID 36354040Accessed 2 Oct 2026
  12. 12Retatrutide-Associated Improvements in Cardiovascular Risk Biomarkers in Adults With Obesity With or Without Type 2 Diabetes.Diabetes, obesity & metabolism · 2026PMID 42608321Accessed 2 Oct 2026
  13. 13Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2, double-blind, parallel-group, placebo-controlled, randomised trial.The lancet. Diabetes & endocrinology · 2025PMID 40609566Accessed 2 Oct 2026
  14. 14PubMed search: (retatrutide[tiab] OR LY3437943[tiab]) AND (tirzepatide[tiab] OR Mounjaro[tiab] OR Zepbound[tiab] OR LY3298176[tiab])PubMed · 2026pubmed.ncbi.nlm.nih.govAccessed 2 Oct 2026
  15. 15Tirzepatide Once Weekly for the Treatment of Obesity.The New England journal of medicine · 2022PMID 35658024Accessed 2 Oct 2026

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