Retatrutide / Guide

Retatrutide trial results: phase 2 and phase 3

Retatrutide has produced some of the largest weight losses seen in obesity drug trials, but it isn't approved anywhere yet. These are the published numbers, dose by dose.

By PeptideTracker editorial team · Updated November 8, 2026 · 13 sources

[00] Short answer

  1. Phase 2 (NEJM 2023): in 338 adults with obesity, average weight change at 48 weeks was −8.7% (1 mg), −17.1% (4 mg), −22.8% (8 mg) and −24.2% (12 mg), vs −2.1% on placebo1.
  2. Phase 3 TRIUMPH-1 (NEJM 2026): in 2,339 adults without diabetes, weight change at 80 weeks was −17.6%, −23.7% and −25.0% on 4, 9 and 12 mg, vs −3.9% on placebo3.
  3. Side effects were mostly stomach and gut problems. In TRIUMPH-1, Lilly reported nausea in 42.4% on 12 mg vs 14.8% on placebo5.
  4. Retatrutide isn't approved in any country. Lilly plans to apply to FDA in the first quarter of 2027, and says it's legally available only in its trials5–6.

What did the retatrutide phase 2 trial show?

In the 2023 phase 2 trial, adults on retatrutide 12 mg once a week lost an average of 24.2% of their body weight at 48 weeks, compared with 2.1% on placebo1. The trial enrolled 338 adults with a BMI of 30 or more, or 27 to 30 with at least one weight-related condition. They were randomly assigned to 1 mg, 4 mg, 8 mg or 12 mg once a week, or placebo, for 48 weeks1.

Retatrutide phase 2 obesity trial: average weight change and share of people reaching each weight-loss level (NEJM 2023)
GroupWeight change, 24 weeksWeight change, 48 weeksLost 5% or moreLost 10% or moreLost 15% or more
Placebo-1.6%-2.1%27%9%2%
1 mg-7.2%-8.7%Not reportedNot reportedNot reported
4 mg-12.9%-17.1%92%75%60%
8 mg-17.3%-22.8%100%91%75%
12 mg-17.5%-24.2%100%93%83%

Weight-loss levels are at 48 weeks. The 4 mg and 8 mg rows combine the groups that started at 2 mg and at 4 mg. Least-squares means. Trial doses, not a recommendation.

A second phase 2 trial tested retatrutide in 281 adults with type 2 diabetes. At 24 weeks, HbA1c fell by up to 2.02 percentage points on 12 mg, compared with 0.01 on placebo and 1.41 on dulaglutide 1.5 mg. At 36 weeks, weight fell by up to 16.94% on 12 mg, compared with 3.00% on placebo2.

What side effects did the phase 2 trials report?

The most common side effects of retatrutide in phase 2 were stomach and gut problems. In the obesity trial they rose with the dose, were mostly mild to moderate, and were partly reduced by starting at 2 mg rather than 4 mg1. Heart rate also went up with the dose, peaked at 24 weeks, then came down1.

In the type 2 diabetes trial, 35% of people on retatrutide had mild to moderate nausea, diarrhea, vomiting or constipation. That ranged from 13% at the lowest dose to 50% in one 8 mg group, compared with 13% on placebo and 35% on dulaglutide. There was no severe low blood sugar and no deaths2.

What has the TRIUMPH phase 3 program found?

Four TRIUMPH phase 3 trials have reported, and every dose tested beat placebo for weight loss. Two are published in medical journals. The other two are so far known only from Lilly's press releases, which are company statements, not peer-reviewed results.

Retatrutide TRIUMPH phase 3 trials: average weight change by dose (once weekly)
TrialWho took partLengthWeight changeSource
TRIUMPH-132,339 adults with obesity or overweight, no diabetes80 weeks4 mg: -17.6% · 9 mg: -23.7% · 12 mg: -25% · placebo: -3.9%Peer-reviewed (NEJM 2026)
TRIUMPH-241,152 adults with obesity or overweight and type 2 diabetes80 weeks4 mg: -11.9% · 9 mg: -16.8% · 12 mg: -18.8% · placebo: -5.1%Peer-reviewed (Lancet 2026)
TRIUMPH-361,949 adults with severe obesity (BMI 35 or more) and heart or blood vessel disease80 weeks9 mg: -21.6% · 12 mg: -22.6% · placebo: -3.2%Company statement, efficacy estimand
TRIUMPH-48445 adults with obesity or overweight and knee osteoarthritis, no diabetes68 weeks9 mg: -20% · 12 mg: -23.7% · placebo: -4.6%Company statement, treatment-regimen estimand

The two ways of counting give different numbers. The treatment-regimen estimand includes everyone randomized, whether or not they kept taking the drug. Lilly's efficacy estimand estimates what would have happened if everyone had stayed on treatment3,6, so it's higher. For TRIUMPH-1 at 12 mg, it's 25.0% one way and 28.3% the other3,5.

  • Knee pain: in TRIUMPH-4, Lilly reported knee osteoarthritis pain scores (WOMAC) fell by up to 4.5 points from an average of 6.08. In the knee osteoarthritis group of TRIUMPH-1, it reported up to 4.3 points9.
  • Heart events: in TRIUMPH-3, Lilly reported 44 major heart and blood vessel events on retatrutide and 52 on placebo (hazard ratio 0.82, 95% CI 0.55 to 1.22). The range includes no difference, and Lilly said events were fewer than expected in both groups6.
  • Type 2 diabetes: in TRIUMPH-2, people on retatrutide had more hypotension (low blood pressure) and dysesthesia than on placebo4.

What side effects were reported in the retatrutide phase 3 trials?

Nausea, diarrhea, constipation and vomiting were the most common side effects in TRIUMPH-1, and they were more common at higher doses5. Lilly also reported dysesthesia, an unusual or unpleasant skin sensation, more often on retatrutide than on placebo5.

TRIUMPH-1 side effects, percent of adults (Lilly press release, May 21, 2026)
Side effectPlacebo4 mg9 mg12 mg
Nausea14.8%28.6%38.4%42.4%
Diarrhea13.5%25.2%34.1%32%
Constipation10.9%23.8%25.9%26.1%
Vomiting4.8%10.6%22.8%25.3%
Dysesthesia (odd skin sensations)0.9%5.1%12.3%12.5%
Urinary tract infection5.3%7.5%8.8%8.4%
Stopped because of side effects4.9%4.1%6.9%11.3%

Company statement. Lilly said dysesthesia and urinary tract infections were generally mild to moderate and most resolved during treatment.

Rates differed between trials. In TRIUMPH-4, Lilly reported dysesthesia in 8.8% on 9 mg and 20.9% on 12 mg, vs 0.7% on placebo, and 12.2% and 18.2% stopped because of side effects, vs 4.0%. Lilly said stopping was linked to starting BMI and included people who felt they'd lost too much weight8. In TRIUMPH-2, 12% on 9 mg and 8% on 12 mg stopped for side effects or death, vs 5% on placebo. Seven people died across all groups, and investigators judged none of the deaths related to the study drug4.

The GLP-1 side effects guide compares the approved medicines' label rates.

Is retatrutide approved anywhere?

No. Lilly describes retatrutide as an investigational molecule that cannot be legally sold or marketed for human use7, legally available only to people in its clinical trials5. Lilly says it's completing the manufacturing data package and plans to apply for US approval in the first quarter of 20276. Approval would come only after FDA review.

  • US: FDA says retatrutide cannot be used in compounding, isn't part of any approved drug, and hasn't been found safe and effective for any condition. It has warned companies selling retatrutide labeled “for research purposes”10.
  • UK: the MHRA says retatrutide is not authorised in the UK, and products sold as retatrutide outside clinical trials are supplied illegally. In October 2026 it seized over 12,000 fake retatrutide and tirzepatide pens11.
  • Canada: Health Canada lists retatrutide among unauthorized injectable peptides it has seized12, and no retatrutide product is in its drug database13.

Questions

How much weight did people lose on retatrutide in the phase 2 trial?

At 48 weeks, average weight change was -8.7% on 1 mg, -17.1% on 4 mg, -22.8% on 8 mg and -24.2% on 12 mg once a week, compared with -2.1% on placebo, in 338 adults with obesity (NEJM 2023).

What were the TRIUMPH-1 results?

In 2,339 adults with obesity and without diabetes, average weight change at 80 weeks was -17.6% on 4 mg, -23.7% on 9 mg and -25.0% on 12 mg, compared with -3.9% on placebo (NEJM 2026). Lilly's efficacy estimand, which assumes everyone stayed on treatment, gave 28.3% at 12 mg.

What are the side effects of retatrutide?

Mostly nausea, diarrhea, constipation and vomiting, more often at higher doses. Trials also reported dysesthesia (odd skin sensations), up to 20.9% on 12 mg in TRIUMPH-4 per Lilly, and more low blood pressure than placebo in TRIUMPH-2. Heart rate rose with dose in phase 2.

When will retatrutide be approved?

It isn't approved anywhere as of November 8, 2026. Lilly plans to submit it to FDA in the first quarter of 2027. Any approval would come after FDA's review, so there's no confirmed date.

Is retatrutide better than tirzepatide?

No published trial has compared them head to head. Weight loss figures from different trials can't be compared directly, because the people, trial lengths and methods differ.

Is retatrutide available in the UK?

No. The MHRA says retatrutide isn't authorised in the UK and that products sold as retatrutide outside clinical trials are being supplied illegally.

Sources

Checked against the phase 2 trials (NEJM 2023, Lancet 2023), TRIUMPH-1 (NEJM 2026) and TRIUMPH-2 (Lancet 2026) on PubMed, and Eli Lilly press releases for readouts not yet published. How we check

  1. 1Jastreboff AM et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med. 2023;389:514-526
  2. 2Rosenstock J et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a phase 2 trial. Lancet. 2023;402:529-544
  3. 3Jastreboff AM et al. Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1). N Engl J Med. 2026;395:1781-1793. treatment-regimen estimand
  4. 4Bellido V et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2). Lancet. 2026;408:1455-1472. treatment-regimen estimand
  5. 5Eli Lilly press release: retatrutide delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH-1), May 21, 2026. company statement; adverse events and discontinuation rates
  6. 6Eli Lilly press release: retatrutide successful in two additional Phase 3 obesity trials (TRIUMPH-2 and TRIUMPH-3), July 23, 2026. company statement; TRIUMPH-3 results, MACE analyses, estimand definition and regulatory plans
  7. 7Eli Lilly press release: retatrutide delivered substantial weight loss and A1C reduction (TRIUMPH-2), September 29, 2026. company statement; investigational status
  8. 8Eli Lilly press release: retatrutide delivered weight loss of up to an average of 71.2 lbs along with relief from osteoarthritis pain (TRIUMPH-4), December 11, 2025. company statement
  9. 9Eli Lilly press release: retatrutide drove improvements in weight, A1C, knee osteoarthritis pain and obstructive sleep apnea (ADA 2026), June 6, 2026. company statement
  10. 10FDA: FDA's concerns with unapproved GLP-1 drugs used for weight loss
  11. 11MHRA: Counterfeit weight loss pens worth £2 million seized by MHRA and West Midlands Police, October 15, 2026
  12. 12Health Canada: Think twice before injecting peptides bought online (public advisory RA-81874). published April 9, 2026
  13. 13Health Canada Drug Product Database, active ingredient search for retatrutide. no products found, searched November 8, 2026

This guide explains what labels and published studies say. It isn't medical advice and doesn't replace your prescriber or pharmacist.

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