Retatrutide vs tirzepatide (Zepbound): which is better?

Retatrutide is not FDA approved

Tirzepatide is approved as Zepbound and Mounjaro. Retatrutide is still in testing. FDA status, proof and safety are rated separately.

By the Peptide Science Desk Editorial TeamFact-checked against FDA and official sources · Oct 30, 2026Not yet reviewed by a licensed clinician. How we check facts

Short answer: Nobody can say yet. In separate trials, retatrutide led to more weight loss (25.0% in TRIUMPH-1) than Zepbound (tirzepatide) did (20.9% in its main trial). But the trials had different people and lengths. The real head-to-head trial, TRIUMPH-5, has not reported. Stomach side effects look similar or a bit higher with retatrutide. The biggest difference: Zepbound is FDA approved, and retatrutide is not. "Reta" sold online is not the tested drug.

A scientist looks into a microscope in a lab — A scientist looks at a slide under a microscope (2005 photo).Photo: Diane A. Reid, National Cancer Institute (NIH), public domain

Is retatrutide better than tirzepatide?

We do not know yet. No finished trial has put them side by side.
Lilly, which makes both, is running TRIUMPH-5. It compares retatrutide with tirzepatide in about 800 adults with obesity for 80 weeks.
ClinicalTrials.gov lists its main finish date as November 2026. Results come after that.
Retatrutide has now been tested head to head against one approved drug: Ozempic 2 mg (semaglutide), in TRANSCEND-T2D-2. Lilly reported on Oct 28, 2026 that it lowered A1C more (2.2% vs 1.8%) and led to more than double the weight loss (19.5% to 20.9% vs 9.4%) in adults with type 2 diabetes over 80 weeks. That says nothing directly about tirzepatide.

Retatrutide vs tirzepatide: how much weight did people lose?

Retatrutide, TRIUMPH-1 (2,339 adults without diabetes, 80 weeks): 25.0% at the highest dose vs 3.9% on placebo.
Zepbound, main FDA label trial (adults without diabetes, 72 weeks): 20.9% at the highest dose vs 3.1% on placebo.
In people with type 2 diabetes: retatrutide 18.8% vs 5.1% (TRIUMPH-2, 80 weeks); Zepbound 14.7% vs 3.2% (72 weeks).
Different trials cannot be compared directly. The retatrutide trials were 8 weeks longer.

Why does Lilly say 20.8% but the paper says 18.8%?

Both are about TRIUMPH-2. They count people in 2 different ways.
The Lancet paper's main result (18.8% vs 5.1%) counts everyone who started, even people who stopped the drug.
Lilly's news release (20.8% vs 4.0%) estimates what would happen if everyone stayed on the drug.
Neither is wrong. The first one is closer to what happens in real life, because some people stop.

Retatrutide vs tirzepatide side effects

Both mostly cause stomach side effects: nausea, diarrhea, vomiting and constipation.
At the highest dose, nausea was 28% on both (vs 8% on placebo). Diarrhea was 34% on retatrutide in TRIUMPH-2 vs 23% on Zepbound.
In TRIUMPH-2, retatrutide also caused more low blood pressure (up to 6% vs under 1%) and dysesthesia, an odd skin feeling like tingling (up to 7% vs 1%).
More people stopped retatrutide because of side effects at the 2 higher doses (12% and 8%) than on placebo (5%).

How do retatrutide and tirzepatide work?

Tirzepatide acts on 2 gut hormone signals: GLP-1 and GIP.
Retatrutide acts on 3: GLP-1, GIP and glucagon. That is why people call it a "triple agonist" or "triple G."
Both are weekly shots in the trials.

Is retatrutide FDA approved like tirzepatide?

No. Tirzepatide is FDA approved as Zepbound (weight loss and sleep apnea) and Mounjaro (type 2 diabetes).
Retatrutide is not approved for anything. Lilly says it plans to apply in early 2027.
On Oct 2, 2026, the FDA said retatrutide counts as a drug, not a biologic. That is about which rules apply, not an approval.

Is "retatrutide" sold online real?

Lilly says any product claiming to be retatrutide outside its clinical trials is unlawful, and it does not sell it to the public.
You may see a "Retatrutide Pen" on DailyMed, a US government drug label website. That listing was posted by a Chinese e-commerce company and is marked "Export only." A listing is not an FDA approval.
Online "reta" has not been tested like the trial drug, so its strength and purity are unknown.

The numbers in charts

Retatrutide vs tirzepatide: weight lost in big trials

Average % of body weight lost at the highest dose vs placebo. Separate trials, not head to head.

Retatrutide: TRIUMPH-1not approved2,339 adults, no diabetes · 80 weeks

−25.0%

−3.9%

Zepbound (tirzepatide): Study 1FDA label · 2,539 adults, no diabetes · 72 weeks

−20.9%

−3.1%

Retatrutide: TRIUMPH-2not approved1,152 adults with type 2 diabetes · 80 weeks

−18.8%

−5.1%

Zepbound (tirzepatide): Study 2FDA label · adults with type 2 diabetes · 72 weeks

−14.7%

−3.2%

Retatrutide numbers are each journal paper’s main result, which counts everyone who started. Lilly’s news releases use "if everyone stayed on the drug" math and show bigger numbers (TRIUMPH-2: 20.8% vs 4.0%).

Show the numbers as a table

Retatrutide vs tirzepatide: weight lost in big trials: Average % of body weight lost at the highest dose vs placebo. Separate trials, not head to head.
Trial	On the drug (highest dose)	On placebo
Retatrutide: TRIUMPH-1 (not approved) 2,339 adults, no diabetes · 80 weeks	−25.0%	−3.9%
Zepbound (tirzepatide): Study 1 FDA label · 2,539 adults, no diabetes · 72 weeks	−20.9%	−3.1%
Retatrutide: TRIUMPH-2 (not approved) 1,152 adults with type 2 diabetes · 80 weeks	−18.8%	−5.1%
Zepbound (tirzepatide): Study 2 FDA label · adults with type 2 diabetes · 72 weeks	−14.7%	−3.2%

Retatrutide trials were 8 weeks longer, so this is not a fair race. The real head-to-head trial, TRIUMPH-5, has not reported yet. Sources: Jastreboff et al., Retatrutide for obesity (TRIUMPH-1), NEJM 2026 (PMID 42814954); Bellido et al., Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2), Lancet 2026 (PMID 42810372); Zepbound (tirzepatide), FDA label (Aug 2026); ClinicalTrials.gov: TRIUMPH-5, retatrutide vs tirzepatide (NCT06662383).

Retatrutide vs tirzepatide: stomach side effects at the highest dose

% of people with nausea or diarrhea, drug vs placebo

Nausea: retatrutidenot approvedTRIUMPH-2, 12 mg

28%

Nausea: Zepbound (tirzepatide)FDA label, 15 mg

28%

Diarrhea: retatrutidenot approvedTRIUMPH-2, 12 mg

34%

13%

Diarrhea: Zepbound (tirzepatide)FDA label, 15 mg

23%

Doses are shown only to say which trial group the numbers come from. They are not advice.

Show the numbers as a table

Retatrutide vs tirzepatide: stomach side effects at the highest dose: % of people with nausea or diarrhea, drug vs placebo
Side effect (source)	On the drug	On placebo
Nausea: retatrutide (not approved) TRIUMPH-2, 12 mg	28%	8%
Nausea: Zepbound (tirzepatide) FDA label, 15 mg	28%	8%
Diarrhea: retatrutide (not approved) TRIUMPH-2, 12 mg	34%	13%
Diarrhea: Zepbound (tirzepatide) FDA label, 15 mg	23%	8%

TRIUMPH-2 was in people with type 2 diabetes. The Zepbound numbers are pooled from its weight-loss trials. Different people, so compare with care. Sources: Bellido et al., Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2), Lancet 2026 (PMID 42810372); Zepbound (tirzepatide), FDA label (Aug 2026).

More charts: Peptides by the numbers

The big trials behind these numbers

All were paid for by Eli Lilly, which makes both drugs.

Study type	People	Main finding	Limits
Phase 3 trial, TRIUMPH-1 (retatrutide)	2,339	Up to 25.0% weight loss vs 3.9% at 80 weeks	Not yet reviewed by FDA
Phase 3 trial, TRIUMPH-2 (retatrutide)	1,152	Up to 18.8% vs 5.1% at 80 weeks in type 2 diabetes	More stops due to side effects at higher doses
FDA label trials (Zepbound)	2,539 in Study 1	Up to 20.9% vs 3.1% at 72 weeks	Reviewed by FDA
Head-to-head trial, TRIUMPH-5	About 800 (planned)	No results yet; main finish date November 2026	Still running

Retatrutide vs tirzepatide at a glance

	Retatrutide	Tirzepatide (Zepbound, Mounjaro)
FDA approved?	No, still in testing	Yes
Hormone signals it acts on	3: GLP-1, GIP, glucagon	2: GLP-1, GIP
Weight loss, main trial, no diabetes	25.0% vs 3.9% (80 weeks)	20.9% vs 3.1% (72 weeks)
Weight loss, type 2 diabetes	18.8% vs 5.1% (80 weeks)	14.7% vs 3.2% (72 weeks)
Most common side effects	Nausea, diarrhea, vomiting	Nausea, diarrhea, vomiting, constipation
Head-to-head trial vs each other	TRIUMPH-5: still running	TRIUMPH-5: still running
Head-to-head vs Ozempic 2 mg	TRANSCEND-T2D-2 (type 2 diabetes): 19.5% to 20.9% vs 9.4% weight loss (Lilly, Oct 2026)	Not part of that trial
Can a doctor prescribe it?	No (only in trials)	Yes

Check any peptide in 1 secondFree FDA Status Checker: approved, being tested, or not proven.

FAQ

Which loses more weight, retatrutide or tirzepatide?

In separate trials retatrutide showed more, but no finished trial compared them directly. TRIUMPH-5 will.

Has retatrutide been compared with Ozempic?

Yes. In TRANSCEND-T2D-2 (Lilly, Oct 28, 2026), retatrutide led to 19.5% to 20.9% weight loss vs 9.4% on Ozempic 2 mg in adults with type 2 diabetes over 80 weeks. The full paper is not published yet.

Is retatrutide stronger than Zepbound?

It acts on one more hormone signal (glucagon). Whether that makes it better for you is not known yet.

When will retatrutide be approved?

Lilly plans to apply in early 2027. FDA review takes time after that, and approval is not guaranteed.

Can I switch from Zepbound to retatrutide?

Not legally outside a clinical trial. Retatrutide is not approved. Talk to your doctor before changing any medicine.

Does retatrutide cost more than tirzepatide?

There is no legal price for retatrutide, because it is not sold. Zepbound has maker cash prices; see our GLP-1 pill vs shot tool.

We never share doses or tell you where to buy. Always ask your doctor. Print our doctor questions sheet.

Sources

Not medical advice. Medical disclaimer.