What do trials show about retatrutide side effects and results?
Under the TRIUMPH-1 efficacy estimand (NCT05929066), the 12 mg group lost an average 28.3% of body weight at 80 weeks, versus 2.2% with placebo. The trial enrolled adults with obesity or overweight, a weight-linked condition, and no diabetes. Lilly's release says 2,339 people were randomized and gives no confidence interval. ClinicalTrials.gov now lists actual enrollment of 2,335, so the source counts differ. Both records were checked 21 August 2026. Eli Lilly is the lead sponsor and reported the result. Retatrutide side effects most often involved the gut across the human trials reported below.
The TRIUMPH-1 figure was sponsor-reported rather than published in a peer-reviewed full results paper when PubMed was checked on 21 August 2026. Peer-reviewed Phase 2 and Phase 3 results are reported separately below.
What is retatrutide?
GSRS lists Retatrutide, LY3437943, and LY-3437943 as names for the same base substance. It assigns that substance UNII NOP2Y096GV. The database lists retatrutide sodium under a separate UNII, LQ42M82ZU6. This page therefore does not treat the salt as an alias of the base form.
The Phase 2 obesity paper calls the compound an agonist of GIP, GLP-1, and glucagon receptors. That claim appears in PMID 37366315 and was checked on 21 August 2026.
What retatrutide results have human trials reported?
The studies ask separate questions in separate groups. The table keeps sponsor topline and peer-reviewed findings apart.
| Evidence | Population and sample | Measured result | Interval, funding, and verification |
|---|---|---|---|
TRIUMPH-1 Phase 3 sponsor release, NCT05929066 | Adults with obesity or overweight and a weight-related condition, without diabetes; Lilly reports 2,339 randomized, while the registry lists 2,335 actual | Under the efficacy estimand at 80 weeks, mean body-weight change was -19.0% at 4 mg, -25.9% at 9 mg, -28.3% at 12 mg, and -2.2% with placebo. Under the treatment-regimen estimand, it was -17.6%, -23.7%, -25.0%, and -3.9%, respectively. | The release reports no confidence intervals. Eli Lilly is lead sponsor and reporter; no separate funder is named. Checked 21 August 2026. |
Phase 2 obesity trial, PMID 37366315, NCT04881760 | 338 adults with obesity, or overweight plus a weight-related condition | At 48 weeks, least-squares mean body-weight change was -8.7% at 1 mg, -17.1% in the combined 4 mg groups, -22.8% in the combined 8 mg groups, -24.2% at 12 mg, and -2.1% with placebo | The PubMed abstract reports no confidence intervals for these values. Funded by Eli Lilly. Checked 21 August 2026. |
Phase 2 type 2 diabetes trial, PMID 37385280, NCT04867785 | 281 adults with type 2 diabetes; 275 entered the efficacy analysis | At 36 weeks, body weight fell by a mean 16.94% in the 12 mg group, versus 3.00% with placebo and 2.02% with dulaglutide | The abstract reports standard errors, not confidence intervals, for these values. Funded by Eli Lilly. Checked 21 August 2026. |
Phase 2 liver-fat substudy, PMID 38858523, NCT04881760 | 98 adults from the obesity trial with at least 10% liver fat | At 24 weeks, mean relative liver-fat change was -42.9%, -57.0%, -81.4%, and -82.4% across the 1, 4, 8, and 12 mg groups, versus +0.3% with placebo | The abstract reports all comparisons as P<0.001 and gives no confidence intervals there. The parent trial discloses Eli Lilly funding. Checked 21 August 2026. |
TRANSCEND-T2D-1 Phase 3, PMID 42250575, NCT06354660 | 537 adults with type 2 diabetes inadequately controlled by diet and exercise | At 40 weeks, mean body-weight change at 12 mg was -15.3% (SE 0.8), versus -2.6% (SE 0.5) with placebo. The HbA1c treatment difference was -1.12 percentage points (95% CI -1.39 to -0.85). | Funded by Eli Lilly. Checked 21 August 2026. |
The TRIUMPH design paper, PMID 41090431, describes more than 5,800 people across four Phase 3 studies. Eli Lilly funded that paper. TRIUMPH-1 and TRIUMPH-2 are basket trials with sleep-apnoea or joint-pain studies nested inside them. TRIUMPH-3 studies people with heart disease. TRIUMPH-4 is a stand-alone knee joint-pain trial. The paper describes trial designs, not outcomes. These points were checked on 21 August 2026.
What retatrutide side effects did the trials record?
Lilly's TRIUMPH-1 release reports the following event rates at 80 weeks. These are sponsor-reported results for NCT05929066, not a peer-reviewed full results paper. Eli Lilly is the lead sponsor and reporter. The source was checked on 21 August 2026.
| Event | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 28.6% | 38.4% | 42.4% | 14.8% |
| Diarrhoea | 25.2% | 34.1% | 32.0% | 13.5% |
| Constipation | 23.8% | 25.9% | 26.1% | 10.9% |
| Vomiting | 10.6% | 22.8% | 25.3% | 4.8% |
| Upper respiratory tract infection | 14.2% | 12.2% | 13.1% | 11.6% |
| Dysesthesia | 5.1% | 12.3% | 12.5% | 0.9% |
| Urinary tract infection | 7.5% | 8.8% | 8.4% | 5.3% |
| Stopped treatment because of an adverse event | 4.1% | 6.9% | 11.3% | 4.9% |
The release says dysesthesia and urinary tract infections were usually mild to moderate. It also says most of those events went away during treatment. Most affected people kept taking retatrutide.
The peer-reviewed trials add findings that the topline table does not cover:
- In
PMID 37366315, gut events were the most common events among 338 adults. The paper describes them as dose-related and mostly mild to moderate. Dose-linked heart-rate rises peaked at week 24 and fell afterwards. Eli Lilly funded the trial; checked 21 August 2026. - In
PMID 37385280, gut events occurred in 67 of 190 people given retatrutide (35%). They occurred in 6 of 45 people given placebo (13%) and 16 of 46 given dulaglutide (35%). The trial recorded no severe low blood sugar and no deaths. Eli Lilly funded the trial; checked 21 August 2026. - In
PMID 42250575, adverse events led 2-5% of people given the drug to stop treatment, versus 0% with placebo. The trial recorded no severe low blood sugar. Two deaths occurred in the 4 mg group, and the authors assessed both as unrelated to the study drug. The trial included 537 adults and was funded by Eli Lilly; checked 21 August 2026.
What retatrutide doses did the studies administer?
The studies did not test one standard retatrutide dose. They tested different weekly amounts in defined populations and monitored the participants. The amounts below describe research arms only.
| Study | Retatrutide amounts studied | Population and duration |
|---|---|---|
NCT04881760, PMID 37366315 | 1 mg, 4 mg, 8 mg, or 12 mg | 338 adults with obesity or overweight; 48 weeks |
NCT04867785, PMID 37385280 | 0.5 mg, 4 mg, 8 mg, or 12 mg | 281 adults with type 2 diabetes; 36 weeks |
NCT06354660, PMID 42250575 | 4 mg, 9 mg, or 12 mg | 537 adults with type 2 diabetes; 40 weeks |
NCT05929066, sponsor topline | 4 mg, 9 mg, or 12 mg | 2,339 randomized in the release and 2,335 actual in the registry; 80 weeks |
The three peer-reviewed trials disclose Eli Lilly funding. ClinicalTrials.gov names Eli Lilly as the lead sponsor for TRIUMPH-1. Every row was checked against its primary record on 21 August 2026.
What has testing found in retatrutide vials?
Direct vial tests and human trials answer separate questions. Trial results do not identify the contents of another vial.
Direct retatrutide testing
A 2026 preprint analysed a public testing-service dataset covering 6,487 reports across 14 peptides. The authors reported 59 retatrutide identity failures. Figure 5 labels the retatrutide abundance-and-purity analysis N=507.
This compound had the highest dual-pass rate among the 14 peptides under both study models. 67.8% met the study's 90-110% label-amount and at least 98% purity thresholds. 47.0% met its 95-105% label-amount and at least 99.5% purity thresholds. The paper does not print a compound-level denominator beside those rates in its text.
Across all 6,285 reports retained for abundance and purity analysis, median measured amount was 101.80% of the label. Median purity was 99.80%. Endotoxin results existed for 243 reports across the full dataset, but the paper gives no retatrutide-specific endotoxin result in its text.
The sample was self-selected rather than random or representative. Buyers and sellers sent samples by choice. The authors say firms sure of their goods may be more likely to take part. Poor batches may therefore be missed. The preprint received no external funding, and its authors declared no conflict of interest.
Source, checked 21 August 2026: Mendias and Awan preprint, DOI 10.20944/preprints202604.1748.v1.
What the peer-reviewed purchase study can establish
The peer-reviewed purchase study tested semaglutide, not retatrutide. The team ordered six products and got three vials. Purity was 7.70%, 14.37%, and 8.97% against labels claiming 99%. Drug content was above the labels by 28.56%, 38.69%, and 33.58%.
Endotoxin was detected in all three vials at 2.1645-8.9511 EU/mg. No viable microorganisms were found at the time of testing. The paper reports no peptide-like impurities. Three selected vials cannot establish a rate for retatrutide or for the wider market.
Source, checked 21 August 2026: Ashraf and colleagues, PMID 39509151, PMCID PMC11582493.
More detail on what different tests can and cannot show is on what is in the vial.
When will retatrutide be available?
The primary sources opened for this page do not give a public sale date. Lilly's 21 May 2026 release calls the compound investigational. ClinicalTrials.gov records Phase 3 studies, but a completed trial is not a marketing authorisation.
Retatrutide did not appear in the EMA centralised medicines workbook on 21 August 2026. The workbook contained 2,731 medicine records. Five semaglutide records and one tirzepatide record were found as positive controls. National medicine registers were not surveyed, so this is a finding about the EMA centralised dataset only.
Primary records: Lilly's TRIUMPH-1 release, ClinicalTrials.gov NCT05929066, and the EMA medicines workbook. All were checked on 21 August 2026.
Where can a reader go next?
The weight-loss research hub compares the main measured findings across compounds. The counterfeit GLP-1 evidence covers tested products sold as semaglutide and tirzepatide. The retatrutide register record separates peer-reviewed results, sponsor toplines, source-reported amounts, user reports and direct vial tests. Neither route ranks one compound as better or safer than another.