Retatrutide vs Tirzepatide: What You Can Learn Before a Direct Test
Retatrutide has Phase 2 findings, while tirzepatide has Phase 3 findings. Only one study using both can compare their benefit and harm fairly.
What retatrutide adds and why the studies aren't equal
Can you tell whether retatrutide beats tirzepatide now? No, because no completed study has tested them against each other.
Tirzepatide is FDA-approved and copies GLP-1, a hunger hormone, plus a meal hormone that affects insulin. Retatrutide isn't approved and also copies glucagon, which may raise calorie use.
Eli Lilly makes both drugs. Glucagon is the extra action that separates the two drugs.
Phase 2 checks benefit and common harm in a mid-size group. Phase 3 uses a much larger group before an approval decision.
Retatrutide's earlier weight change topped tirzepatide's later figure. Since the people and study length differed, those numbers can't name a better drug.
A direct TRIUMPH test has begun, but its results remain unavailable. For now, the figures show only what happened in separate groups, not your likely result.
What added glucagon may do
In your body, both drugs copy GLP-1, the hunger hormone, and a meal hormone that helps insulin work. Retatrutide also copies part of glucagon.
- Tirzepatide: It copies GLP-1 and the meal hormone and is FDA-approved. It doesn't copy glucagon.
- Retatrutide: It copies GLP-1, the meal hormone, and glucagon, and isn't approved. Glucagon may raise calorie use and move fat from the liver [3][6].
Frozen lab samples showed retatrutide touching the protein that reads each hormone [3]. Tests with lab-grown cells showed that the glucagon path worked without sharply raising your sugar [3].
A 2025 review said glucagon may help explain the added weight loss [11]. A second 2025 review asked whether these drugs might improve weight, sugar, liver fat, and heart risk [12].
That second review did not show that both drugs improved every problem in people. Only one trial giving both drugs to like groups can give you that answer.
What the separate Phase 2 retatrutide and Phase 3 tirzepatide studies found
Published Phase 2 figures below help you compare different studies. Differences in the people, study length, and way weight was judged can change the result.
Average body-weight change:
| Drug | Weekly amount | Study | Time | Average change |
|---|---|---|---|---|
| Retatrutide | 12 mg each week | Phase 2 obesity [1] | 48 weeks | −24.2% |
| Retatrutide | 8 mg each week | Phase 2 obesity [1] | 48 weeks | −22.8% |
| Tirzepatide | 15 mg each week | Phase 3 obesity | 72 weeks | about −22.5% |
| Retatrutide (diabetes) | 12 mg each week | Phase 2 diabetes [2] | 36 weeks | −16.94% |
Tirzepatide's figure came from SURMOUNT-1, a longer Phase 3 study with more people. It gives you context but can't settle which medicine would work better for you.
Three-month blood-sugar change in type 2 diabetes:
- Retatrutide 12 mg in Phase 2: −2.02%, compared with −0.01% for placebo, the shot without retatrutide, at 24 weeks [2].
- Tirzepatide's Phase 3 diabetes studies found drops of −1.87% to −2.09% at the top amounts over 40 weeks.
Liver fat in fatty liver disease:
- Retatrutide 12 mg in the liver study: −82.4% at 24 weeks [5].
- Tirzepatide: Phase 3 liver findings were still coming out. Its Phase 2 work showed drops, but by mid-2026 the published Phase 3 figures were less complete.
What each drug may do to your stomach, pulse, and muscle
Both drugs can upset your stomach with nausea, vomiting, or diarrhea. These problems often make a person stop treatment.
- Heart rate: Retatrutide raised the average by about 5–7 beats per minute, peaking near week 24 [1]. The Phase 3 source calls tirzepatide's rise smaller but gives no number here, so you can't compare the size fairly.
- Stopping for stomach trouble: At 12 mg, retatrutide had an 18% stop rate from those problems [1]. The Phase 3 source gives no exact tirzepatide rate beside the Phase 2 retatrutide rate, so you can't compare the rates.
- Muscle loss: Both drugs can reduce muscle. A 2025 retatrutide study measured both muscle loss and fat loss [4].
- Long-term health: Tirzepatide finished Phase 3 work in diabetes and obesity and now has approved uses. Retatrutide's long-term studies remain under way [9][10].
No trial has tested their safety side by side. The separate findings can't show which choice would carry less risk for you.
What the direct TRIUMPH study may settle
Eli Lilly's TRIUMPH Phase 3 work includes a study that gives people retatrutide or tirzepatide. No results were available in mid-2026.
Only that kind of study can compare benefit and harm in the same sort of people under the same rules. Until it reports, retatrutide results can only tell you what retatrutide did in its own studies.
What approval changes about your access and safety facts
Tirzepatide: It gained FDA approval for type 2 diabetes in 2022 and obesity in 2023. A licensed health worker can prescribe it.
Retatrutide: The drug has no approval, so a prescription isn't available to you. It remains in active Phase 3 studies [7][9][10], with no approval request filed by mid-2026.
That gap matters in real life. Tirzepatide has an approved schedule and reports gathered over years from people using it outside studies.
Retatrutide doesn't yet have that safety record. Its Phase 3 studies and later review must build the facts you would need.