Quick answer: no retatrutide stack has been tested in people. No published trial or registered study combines retatrutide with tirzepatide, tesamorelin, MOTS-c or testosterone (TRT). Retatrutide itself is investigational and not FDA-approved, and FDA says it cannot be used in compounding.[1] What is known comes from studies of each drug on its own, and that is what this page sets out.

Retatrutide is Eli Lilly’s once-weekly triple agonist of the GIP, GLP-1 and glucagon receptors. For the trial evidence on it alone, see the retatrutide profile, retatrutide side effects and is retatrutide safe?.

What “stacking” means and why there is no data

“Stacking” means taking two or more drugs at once in the hope that their effects add up. It is common in online peptide communities, usually with products sold as “research chemicals”. Our general guide to peptide stacking explains the idea.

Every retatrutide trial so far has tested retatrutide by itself:

  • TRIUMPH-1 gave 2,339 adults with obesity 4, 9 or 12 mg weekly or placebo for 80 weeks. Average weight change was −17.6%, −23.7% and −25.0%, versus −3.9% on placebo.[2]
  • TRIUMPH-2 tested the same doses in 1,152 adults with obesity and type 2 diabetes.[4]
  • TRIUMPH-5 compares retatrutide with tirzepatide in about 800 adults, as separate treatments, not together.[7]

A search of ClinicalTrials.gov and PubMed in October 2026 found no human study of retatrutide combined with cagrilintide, tesamorelin, MOTS-c or testosterone. The only combination data are from rats (see below).

Retatrutide with tirzepatide

This is the most searched combination, and the one with the clearest reason not to do it.

  • They overlap. Tirzepatide (Zepbound, Mounjaro) activates GIP and GLP-1 receptors. Retatrutide activates both of those plus the glucagon receptor.[2] Adding them together doubles up on the same targets.
  • The label says no. Zepbound’s FDA label states that combining it with other tirzepatide-containing products or with any GLP-1 receptor agonist is not recommended.[6] Retatrutide is a GLP-1 receptor agonist.
  • Side effects are dose-related. In TRIUMPH-1, nausea rose from 28.6% on 4 mg to 42.4% on 12 mg, and vomiting from 10.6% to 25.3%. Stopping treatment because of side effects rose from 4.1% to 11.3%.[3] Stacking two drugs in this class would likely push exposure past anything tested.
  • Lilly tests them apart. Even in Lilly’s own liver-outcomes study, SYNERGY-Outcomes, people are randomized to retatrutide, tirzepatide or placebo, never both.[8]

Tirzepatide’s label also warns about severe stomach side effects, acute kidney injury from dehydration, gallbladder disease and pancreatitis.[6] These are the risks that would be expected to grow with higher combined doses. For how the two drugs compare when used separately, see retatrutide vs tirzepatide.

Retatrutide with tesamorelin

Tesamorelin is a growth hormone-releasing factor analog. It is FDA-approved (as Egrifta) for one use: reducing excess abdominal fat in adults with HIV and lipodystrophy. Its label says it is not indicated for weight loss because its effect on weight is neutral.[9]

The label lists warnings that matter if it were combined with a metabolic drug:[9]

  • Glucose intolerance or diabetes. In trials, 5% of people on tesamorelin had a rise in HbA1c to 6.5% or more by week 26, versus 1% on placebo. The label advises checking glucose before and during treatment.
  • Raised IGF-1. It stimulates growth hormone and raises IGF-1, a growth factor. The effects of long-term elevation are unknown.
  • Fluid retention, such as swelling, joint pain and carpal tunnel syndrome.
  • Not for people with active cancer or during pregnancy.

No study has tested tesamorelin with retatrutide or any GLP-1 drug. Retatrutide lowers blood sugar, while tesamorelin can raise it, so the net effect on glucose in one person is unpredictable. For tesamorelin’s own label dosing, see tesamorelin dosage.

Retatrutide with MOTS-c

MOTS-c is a 16-amino-acid peptide made by mitochondria. Its metabolic effects have been studied in rodents and cells.

In a July 2026 review, FDA scientists wrote that they found no clinical studies or human exposure data for MOTS-c by any route, so its safety risks in humans are unknown. They also raised concern about immune reactions to injected MOTS-c because of possible impurities and clumping (aggregation).[10] FDA’s advisory committee still voted 7 to 5, with 2 abstentions, to recommend allowing it in compounding; the vote is not binding.[11]

With no human data on MOTS-c alone, there is nothing to say about MOTS-c plus retatrutide except that it is untested. Our MOTS-c dosage guide explains why no human dose exists.

Retatrutide with TRT

Testosterone replacement therapy (TRT) is a prescription treatment for men with confirmed low testosterone. No trial has studied retatrutide in people taking testosterone, and none is registered.

What can be said is general: rapid weight loss changes many things a TRT prescriber monitors, so anyone on testosterone who starts any weight-loss medicine should tell the clinician managing both. For how TRT differs from peptide treatments, see peptides vs TRT.

Retatrutide with cagrilintide: rat data only

Cagrilintide is Novo Nordisk’s amylin analog, tested in people only with semaglutide (as CagriSema). A 2026 study in obese male rats found that daily retatrutide plus cagrilintide reduced weight and food intake more than either drug alone.[13] That is an animal result, and it has not been tested in people. Our page on cagrilintide with retatrutide covers it in detail.

The bigger risk: what is in the vial

Retatrutide is not approved; Lilly plans to submit it to the FDA in the first quarter of 2027.[14] FDA has warned companies selling retatrutide “for research purposes” or “not for human consumption” and says these products are of unknown quality.[1]

A 2026 study of 13,589 social media users describing their own unapproved retatrutide use found a symptom pattern unlike the trials, led by increased appetite, fatigue and insomnia. The authors noted that the reports may reflect product or dose variability and “peptide stacking”, the concurrent use of several unapproved peptides.[12] Combining several unverified products makes it impossible to know which one caused a problem.

What the trials did show about retatrutide alone

To keep this in perspective, retatrutide on its own produced large weight loss with mostly stomach-related side effects. In TRIUMPH-2, dysesthesia (abnormal skin sensation) affected 4% to 7% versus 1% on placebo, and low blood pressure up to 6% versus under 1%.[4] In phase 2, heart rate rose with dose, peaked at 24 weeks and then declined.[5] Any of these could interact with a second drug in ways no one has measured.

Questions to ask a clinician

  • Is an approved medicine such as tirzepatide or semaglutide right for me on its own?
  • Would I qualify for a retatrutide clinical trial, with proper monitoring?
  • I take testosterone (or another hormone). What would need checking if I started a weight-loss drug?
  • How should we manage muscle loss or side effects without adding unproven products?

For the doses tested in trials, see the retatrutide dosage guide, and for the legal picture, is retatrutide legal?.