Retatrutide vs tirzepatide: limits of comparison.

What one extra hormone action may change

Of these two drugs, retatrutide remains under study while tirzepatide is approved. This retatrutide vs tirzepatide page explains the key difference and the separate study results. Tirzepatide copies GLP-1 and GIP. Retatrutide adds glucagon as a third action.

In its Phase 2 trial, people on retatrutide's highest dose dropped an average 24.2% over 48 weeks ^[1]. People on tirzepatide's highest dose lost about 20-22% in a separate Phase 3 trial. The people and study rules differed, so these figures do not prove which drug works better. A direct Phase 3 TRIUMPH vs tirzepatide trial has not reported yet.

This page keeps that limit in view for you. It explains each result without calling retatrutide better. The direct trial is fairer because both drugs are studied under the same rules.

What the third hormone action does in retatrutide

Both drugs act at the hormone targets for GLP-1 and GIP. The first action can curb hunger and slow the stomach from emptying. After a meal, GIP prompts insulin release. Together, those actions help with weight and blood sugar.

Retatrutide also copies glucagon. Blood sugar can rise with glucagon, yet calorie use may climb and liver fat may fall. That sounds odd in a weight drug. The other two hormone actions may help balance the sugar rise.

Close lab pictures placed retatrutide at all three hormone targets ^[3]. GIP was its strongest action, while glucagon was made milder. Those lab facts may explain the design, but they don't predict any person's weight change.

Tirzepatide has no glucagon action. Researchers don't know how much of the gap between separate trials came from glucagon. Differences in the people and study rules could explain part of it too. The head-to-head trial should help sort out that gap for you.

What separate Phase 2/3 trials do not prove

The two drugs were tested in different people under different rules. Weight, diabetes, other illnesses, and study length can all change a result. The main goal measured by each trial can differ as well. Therefore, side-by-side figures give you background, not a direct contest.

In its Phase 2 obesity trial, the 12 mg retatrutide group shed an average 24.2% over 48 weeks. In that group, 63% lost at least 20% of body weight ^[1]. A 2025 review of three retatrutide trials found that people on the drug lost 14.33% more weight on average than people on a dummy shot ^[8]. Those figures cover groups; they cannot predict your result.

A review in the science journal Cell described weight losses of about 20-30% with drugs that copy more than one hormone ^[9]. A 2025 review in the journal Biomolecules called retatrutide's loss of about 24% at 12 mg a large step from older drugs ^[6]. Reviews compare published work; they do not create a direct trial. Weight-loss surgery is also a different kind of care.

Tirzepatide has Phase 3 results and an FDA label for blood-sugar control. In the retatrutide diabetes Phase 2 trial, HbA1c, a blood test of average sugar, fell by 2.02%, against 0.01% on the dummy shot at 24 weeks ^[2]. A fair answer needs the direct trial, where the rules match.

What risks the two drugs share, and what they do not

Both drugs can cause nausea, vomiting, diarrhea, and constipation. Higher doses brought more of these problems. Both trial programs raised amounts slowly to make gut effects easier to bear. Much of the shared trouble comes from the GLP-1 action.

Retatrutide also raised resting pulse. At the top doses, resting pulse rose by an average of about 5-7 beats per minute, with its high point near week 24 ^[1]. Tirzepatide doesn't copy glucagon, so the same pulse effect hasn't stood out. A heart study is checking what the retatrutide rise means over years.

Tirzepatide has finished its own large heart trial, and that trial reported a benefit to the heart. The matching retatrutide trial is still running. Both drugs can reduce lean mass, including muscle, along with fat. Weight can also return after GLP-1-class drugs are stopped ^[13].

Retatrutide isn't approved. Tirzepatide is approved for obesity and type 2 diabetes in several places, including the US. That means tirzepatide has passed Phase 3 review and is watched after sale. Retatrutide hasn't reached those steps.

What the direct TRIUMPH trial will compare

A 2026 Phase 3 trial put retatrutide against tirzepatide directly ^[3]. Both drugs are tested under the same rules, which makes the comparison fairer. Until results arrive, published work doesn't prove that retatrutide is better or worse for a given result. The head-to-head trial will help settle the issue for you.

The Retatrutide references page lists the published papers. The full study guide explains the retatrutide studies in order. Those pages also show which questions remain open.