Tirzepatide vs Retatrutide: differences, evidence and safety

Answer first

Tirzepatide switches on the receptors for two gut hormones, GIP and GLP-1, and is an approved prescription medicine. Retatrutide adds a third, for glucagon, and is approved nowhere; its late-stage results exist only as company press releases. No trial comparing the two has reported, so the figures below come from separate studies and cannot be ranked.

At a glance

How they work

Both drugs are peptides made in the laboratory by the same company, Eli Lilly, and both are chains of 39 amino acid building blocks ^[1], ^[2]. They differ in how many hormone docking points, or receptors, they switch on.

Tirzepatide

• Two receptors, GIP and GLP-1. Its chain copies the gut hormone GIP (glucose-dependent insulinotropic polypeptide) and also switches on the receptor for GLP-1 ^[1].
• Stomach and appetite. Switching on the GLP-1 receptor slows the emptying of the stomach and makes people eat less ^[1].
• Insulin and glucagon. According to the label, the body releases more insulin and less glucagon, the hormone that pushes blood sugar up. Both effects only come into play when blood sugar is high ^[1].

Retatrutide

• Three receptors, GIP, GLP-1 and glucagon. In laboratory tests it is more active at the GIP receptor than at the other two ^[3].
• Stomach. A dedicated early-stage study confirmed that the stomach empties more slowly in people ^[4].
• The glucagon part. The idea is that this receptor raises the energy the body burns and changes how the liver handles fat. No direct measurement of this in people could be found in the sources reviewed for this page ^[3].

The glucagon receptor is the core difference. Glucagon on its own pushes blood sugar up. The published explanation for why blood sugar still falls is that the two gut hormone effects outweigh it ^[3]. For neither drug could a trial be found in the sources reviewed for this page that separates what each receptor contributes in people ^[1], ^[3].

Both carry a fatty acid chain that makes them cling to albumin, a carrier protein in the blood. The body takes about five days to clear half a dose of tirzepatide and about six days for retatrutide ^[1], ^[5].

What the studies show

No study that compares tirzepatide and retatrutide directly could be found in the published record reviewed for this page. The one trial built for that purpose, TRIUMPH-5, is registered with 800 participants. It is under way, no longer recruiting, and has not reported ^[6].

Everything below therefore comes from separate trials. They enrolled different people, gave different doses, measured different endpoints and ran for different lengths of time. Their numbers cannot be set against each other. The level of checking differs too: by 6 September 2026 not one late-stage retatrutide trial had been published in full ^[6].

Weight in adults without diabetes

Phase 3 RCT SURMOUNT-1 allocated 2,539 adults with obesity and without diabetes at random to tirzepatide or to a dummy injection, and followed them for 72 weeks. Average weight fell by 15.0%, 19.5% and 20.9% across the three doses tested, against 3.1% on placebo ^[7].

Phase 2 RCT In a mid-stage trial, 338 adults with obesity received one of four retatrutide doses or a dummy injection for 48 weeks. Their weight fell by 8.7%, 17.1%, 22.8% and 24.2% from the lowest to the highest dose, against 2.1% on placebo ^[8].

Phase 3 (press release only) TRIUMPH-1 followed 2,339 adults without diabetes for 80 weeks. The manufacturer reported losses of 19.0%, 25.9% and 28.3% across three retatrutide doses, against 2.2% on placebo. No independent experts have checked these figures yet ^[9].

Weight in adults with type 2 diabetes

Phase 3 RCT SURMOUNT-2 enrolled 938 adults who had obesity together with type 2 diabetes. By week 72 the two tirzepatide groups had lost 12.8% and 14.7% of their weight. The effect was smaller than in people without diabetes, a pattern also seen with other drugs of this class ^[10].

Phase 3 (press release only) TRIUMPH-2 followed 1,152 adults with type 2 diabetes for 80 weeks. The reported weight loss was 12.7%, 19.1% and 20.8% across three retatrutide doses, against 4.0% on placebo ^[11].

Long-term blood sugar

Both drugs were tested on glycated haemoglobin, a blood value that reflects average blood sugar over the past two to three months.

Phase 3 RCT SURPASS-1 enrolled 478 adults with type 2 diabetes who had not yet taken any diabetes medicine. After 40 weeks the value fell by 1.87 to 2.07 percentage points from a starting level of 7.9%. On placebo it crept up by 0.04 points ^[12].

Phase 3 RCT, open-label SURPASS-2 enrolled 1,879 adults already taking metformin. The value fell by 2.01, 2.24 and 2.30 points across the three tirzepatide doses, compared with 1.86 points on semaglutide ^[13].

Phase 2 RCT A mid-stage trial tested retatrutide in 281 adults with type 2 diabetes. After 24 weeks the value fell by 0.43 points on the lowest dose and 2.02 points on the highest. On placebo it barely moved, at 0.01 points, and on the established drug dulaglutide it fell by 1.41 points ^[14].

Phase 3 (press release only) TRIUMPH-2 reported falls of 1.4 to 1.6 points on retatrutide from a starting value of 7.7% ^[11].

Liver

Phase 2 RCT SYNERGY-NASH treated 190 adults for 52 weeks whose fatty liver had become inflamed and scarred, confirmed by a tissue sample (fibrosis F2 or F3). Among 157 people with an assessable follow-up sample, the inflammation cleared without worse scarring in 44%, 56% and 62% on tirzepatide, against 10% on placebo ^[15].

Phase 2a RCT A retatrutide sub-study enrolled 98 people without diabetes whose livers were at least 10% fat. After 24 weeks, scans showed the fat content down by 42.9%, 57.0%, 81.4% and 82.4% across four doses. On placebo it edged up by 0.3% ^[16].

The two studies measured different things. One judged inflammation and scarring in tissue samples, the other the amount of fat on a scan.

Heart

Phase 3 RCT, active comparator SURPASS-CVOT followed 13,299 adults with type 2 diabetes and hardened arteries for a median of 210.1 weeks, roughly four years. A serious heart event occurred in 12.2% of those on tirzepatide and 13.1% of those on dulaglutide ^[17].

That is a risk 8% lower (hazard ratio 0.92), but the range compatible with the data, 0.83 to 1.01, included no difference at all. The trial showed that tirzepatide is no worse than dulaglutide (p = 0.003); being better was tested and not shown (p = 0.09) ^[17].

Phase 3 RCT SUMMIT followed 731 people who had obesity and the stiff form of heart failure for a median of 104 weeks. Death from a heart cause or worsening heart failure occurred in 9.9% on tirzepatide and 15.3% on placebo (hazard ratio 0.62, range 0.41 to 0.95). Almost all of that came from worsening heart failure ^[18].

Phase 3 (press release only) TRIUMPH-3 enrolled 1,949 adults with severe obesity and diagnosed heart disease. Counted broadly, serious heart events numbered 44 on retatrutide against 52 on placebo (hazard ratio 0.82, range 0.55 to 1.22). Counted narrowly, they numbered 27 against 23 (hazard ratio 1.12, range 0.64 to 1.96) ^[11].

Both retatrutide ranges include no difference, so they show neither a benefit nor a harm. The trial built to answer the question, TRIUMPH-Outcomes, enrols 10,000 people and will not reach its main result before February 2029 ^[19].

Keeping the weight off

Phase 3 RCT, randomised withdrawal In SURMOUNT-4, all 670 participants first took tirzepatide openly for 36 weeks. Between week 36 and week 88 those who carried on lost a further 5.5%, while those switched to placebo regained 14.0% ^[20].

No comparable retatrutide result could be found in the sources reviewed for this page. The longest follow-up is 104 weeks, in an extension limited to people with a body mass index of at least 35 ^[9]. TRIUMPH-6 is testing whether the weight stays off; it is registered with 643 participants and has not reported ^[6].

Outcomes studied for only one of the two

• Tirzepatide and sleep apnoea. SURMOUNT-OSA enrolled 469 adults with obesity and moderate to severe obstructive sleep apnoea. By week 52 breathing interruptions fell by 20.0 and 23.8 events per hour of sleep more than on placebo ^[21].
• Retatrutide and knee pain (press release only). TRIUMPH-4 enrolled 445 adults with worn knee joints. Over 68 weeks their pain score fell by 4.5 and 4.4 points from 6.0, against 2.4 points on placebo. No ranges of uncertainty were published ^[22].

Safety

The two safety records come from very different sources. Tirzepatide's figures come from approved US product information that pools the weight-loss trials. Retatrutide's come only from trials run by the manufacturer, and the late-stage figures only from its press releases. The lists below are therefore not a ranking.

Tirzepatide. The pooled weight-loss trials covered 3,477 people on the drug ^[23].

• Stomach and bowel. Nausea affected 25–29% against 8% on placebo, diarrhoea 19–23% against 8%, vomiting 8–13% against 2% and constipation 11–17% against 5% ^[23].
• Stopping treatment. Side effects led 4.8–6.7% of participants to stop, against 3.4% on placebo ^[23].
• Boxed warning. In rats, tirzepatide causes tumours in the C-cells of the thyroid gland, more often at higher doses and longer exposure. Whether this applies to people is unknown ^[1], ^[23].
• Who must not take it. People with medullary thyroid cancer, personally or in the family, or with the inherited condition multiple endocrine neoplasia type 2 ^[1], ^[23].
• Further label warnings. Pancreas inflammation, kidney damage from fluid loss, gallbladder trouble, low blood sugar alongside insulin and worsening diabetic eye disease ^[1], ^[23].

Retatrutide. The figures compare the highest dose with placebo in TRIUMPH-1 ^[9].

• Stomach and bowel. Nausea affected 42.4% against 14.8%, diarrhoea 32.0% against 13.5%, constipation 26.1% against 10.9% and vomiting 25.3% against 4.8% ^[9].
• Odd skin sensations. Tingling, burning or numbness (dysesthesia) affected 12.5% against 0.9% in TRIUMPH-1. In TRIUMPH-4 it reached 8.8% and 20.9% against 0.7%, mostly mild ^[9], ^[22].
• Stopping treatment. In TRIUMPH-1, 4.1%, 6.9% and 11.3% stopped across the three doses, against 4.9% on placebo ^[9].
• A faster pulse. In the mid-stage trial the heart rate rose with the dose and peaked at week 24 ^[8]. One independent assessment puts the largest rise at 6.7 beats per minute; another flags mild to moderate irregular heartbeat ^[24], ^[25].
• No approved product information. No authority has weighed its benefits against its risks. There is no official list of warnings or of people who must not take it ^[26], ^[27].

A 2026 case report describes a man with type 1 diabetes who injected a product sold online under the retatrutide name. He developed severe vomiting, a dangerous build-up of acids in the blood and sudden kidney damage ^[28].

Why this page lists no doses. Tirzepatide is prescription-only wherever it is approved, and retatrutide is an experimental drug approved nowhere. Choosing an amount is a matter for the product information and the prescribing doctor. This page therefore names doses only by their rank among those tested, from lowest to highest, never as an amount.

Legal status

Tirzepatide is an approved, prescription-only medicine in eight markets. The United States cleared it on 13 May 2022 and the European Union on 15 September 2022; the United Kingdom, Australia, Canada, Switzerland and Japan followed ^[29], ^[30], ^[31]. Retatrutide is approved nowhere; the manufacturer has announced a US application for early 2027 but had not filed it ^[11], ^[26]. In sport, tirzepatide is not on the 2026 prohibited list and has been on the penalty-free monitoring programme since 1 January 2026 ^[32], ^[33]. Retatrutide is banned at all times under section S0, which covers unapproved substances ^[34]. Both monographs reflect the position on 6 September 2026.

Used together?

The myPeptides blend directory lists no product that combines tirzepatide and retatrutide. Its only entry containing retatrutide, Loretta, pairs it with eloralintide, a copy of the appetite hormone amylin; both are in phase 3 and approved nowhere.

No study of the two drugs given together could be found in the sources reviewed for this page. TRIUMPH-5 involves both, but it pits one against the other rather than combining them ^[6]. Retatrutide itself already acts on the GIP and GLP-1 receptors that tirzepatide targets ^[3].

Frequently asked questions

Which is better, tirzepatide or retatrutide?

The evidence does not say. In SURMOUNT-1, among 2,539 adults without diabetes, the highest tested dose of tirzepatide lowered weight by 20.9% over 72 weeks. Retatrutide was not part of that trial; in its own mid-stage trial of 338 adults with obesity, its highest dose lowered weight by 24.2% over 48 weeks. The trial comparing the two directly, TRIUMPH-5, has not reported.

Is tirzepatide or retatrutide safer?

No trial comparing their safety directly could be found in the sources reviewed for this page. Tirzepatide's record comes from approved product information and a heart trial of 13,299 people. It carries a boxed warning about thyroid tumours in rats. Retatrutide's record comes only from the manufacturer's trials, and it includes a faster pulse and odd skin sensations. With both drugs, nausea, diarrhoea, constipation and vomiting are the most common complaints.

What is the difference between tirzepatide and retatrutide?

Tirzepatide switches on two hormone receptors, GIP and GLP-1. Retatrutide switches on those two plus the receptor for glucagon. Tirzepatide is an approved prescription medicine in eight markets. Retatrutide is an experimental drug approved in none, and its late-stage results exist only as press releases.

Can tirzepatide and retatrutide be taken together?

No study of the two drugs given together could be found in the sources reviewed for this page, and the myPeptides blend directory lists no combination of them. The only trial that involves both, TRIUMPH-5, compares one against the other rather than combining them. Retatrutide is approved nowhere, and tirzepatide is available only on prescription.

Is retatrutide just a newer version of tirzepatide?

No. Both come from Eli Lilly and both are chains of 39 amino acids, but retatrutide also acts on the glucagon receptor. The two also stand in completely different legal positions: tirzepatide is approved in eight markets, retatrutide in none.

When will retatrutide be available?

No date can be given. As of 6 September 2026 no country had approved retatrutide, and the manufacturer had announced a US application for early 2027 without having filed it. Since August 2026 a US expanded access programme exists, but it is a compassionate route for a small number of individual cases, not an approval.

Has retatrutide been tested against tirzepatide?

Yes, but without results so far. TRIUMPH-5 is registered with 800 participants and pits retatrutide directly against tirzepatide. It is under way and has not reported, so every comparison published before then rests on separate trials.

Are tirzepatide and retatrutide banned in sport?

Tirzepatide is not on the 2026 prohibited list; it has been on the monitoring programme since 1 January 2026, which carries no penalty. Retatrutide is banned at all times under section S0, which covers substances that no health authority has approved. It falls under the ban because of that status, not because it is named on the list.

How long do tirzepatide and retatrutide stay in the body?

The body takes about five days to clear half a dose of tirzepatide and about six days for retatrutide. In both, a fatty acid chain makes the peptide cling to albumin, a carrier protein in the blood, which slows its removal.