Retatrutide side effects: what trials and regulators have recorded

What are the side effects of retatrutide?

In the Phase 2 obesity trial of 338 adults, funded by the developer, the registry lists gut events most often: nausea in 83 of 267 retatrutide participants (31%) against 8 of 70 on placebo (11%), vomiting in 33 (12%) against 1 (1%), diarrhoea in 37 (14%) against 8 (11%) and constipation in 30 (11%) against 2 (3%), counting only events reported by 5% or more of people in any arm of one small trial (ClinicalTrials.gov NCT04881760). In the 80-week TRIUMPH-2 trial of 1,152 adults with type 2 diabetes, also funded by the developer, nausea affected 14% to 28% of people across the three retatrutide arms against 8% on placebo, a result for that trial population only (Bellido et al., The Lancet, 2026).

In the Phase 2 obesity paper of 338 adults, funded by the developer, the most common adverse events were gut events, they grew with the trial arm level and they were mostly mild to moderate, a description of that trial population only (Jastreboff et al., New England Journal of Medicine, 2023). In the Phase 2 trial of 281 adults with type 2 diabetes, mild to moderate gut events affected 67 of 190 retatrutide participants (35%) against 6 of 45 on placebo (13%), a small early-phase result funded by the developer (Rosenstock et al., The Lancet, 2023).

The table below sets out the Phase 2 registry events side by side. The registry lists events reported by 5% or more of people in any arm, so rarer events do not appear. The pooled counts add the arm counts that the registry reports. For the same question about an approved medicine, tirzepatide's side effects are set out the same way.

Evidence limits

Is retatrutide safe?

Two limits shape every number below. The 2026 Phase 3 papers were read as abstracts only, so their full side-effect tables are not reported here. A trial result also describes trial drug product given under supervision, not a product from any other source.

The last section of this page reports a different kind of record. Regulator alerts and case reports describe products sold as retatrutide, and they cannot give a frequency. They sit apart from the trial figures for that reason.

What serious events have retatrutide trials recorded?

In the Phase 2 obesity trial of 338 adults, the registry lists serious adverse events in 10 of 267 retatrutide participants (4%) and 3 of 70 on placebo (4%), with one death in a retatrutide arm, a small developer-funded trial that cannot show rare events or establish safety (ClinicalTrials.gov NCT04881760). In the Phase 2 obesity trial of 338 adults, the registry lists one case of acute pancreatitis in the highest arm, one of acute cholecystitis (gallbladder inflammation) and one of acute kidney injury, counts too small to show how often such events occur (ClinicalTrials.gov NCT04881760). In TRIUMPH-2, a developer-funded trial of 1,152 adults with type 2 diabetes, seven participants died, six on retatrutide and one on placebo, and the investigators judged every death unrelated to the study intervention (Bellido et al., The Lancet, 2026).

In TRANSCEND-T2D-1, a 40-week developer-funded trial of 537 adults with type 2 diabetes, two deaths were reported, both in the lowest retatrutide arm and judged unrelated to the study drug by the investigators, with no severe hypoglycaemia (Bajaj et al., The Lancet, 2026). The Phase 2 trial of 281 adults with type 2 diabetes reported no deaths and no severe hypoglycaemia, a short early-phase result that cannot show rare events (Rosenstock et al., The Lancet, 2023).

In the Phase 2 obesity trial of 338 adults, the registry lists increased lipase in 15 of 267 retatrutide participants against 2 of 70 on placebo, and increased amylase in 5 against 2, and those are blood-test results that do not establish pancreatitis because the registry does not say how many involved symptoms (ClinicalTrials.gov NCT04881760).

What risks have retatrutide studies recorded besides gut effects?

The Phase 2 obesity paper reports heart-rate increases that grew with the trial arm level, peaked at 24 weeks and declined afterwards in its 338 adults, in a developer-funded trial that describes that population only (Jastreboff et al., New England Journal of Medicine, 2023). In TRIUMPH-2, a developer-funded trial of 1,152 adults with type 2 diabetes, hypotension (low blood pressure) affected 1%, 5% and 6% of people across the retatrutide arms against under 1% on placebo, and dysaesthesia (altered or burning skin sensation) affected 4%, 6% and 7% against 1%, results for that trial population only (Bellido et al., The Lancet, 2026).

In the Phase 2 obesity trial of 338 adults, the registry lists hypertension in 14 of 267 retatrutide participants against 2 of 70 on placebo, hypotension in 6 against 0, hyperaesthesia (raised skin sensitivity) in 7 against 1, and allodynia (pain from a light touch) in 4 against 0, counting only events reported by 5% or more of people in any arm (ClinicalTrials.gov NCT04881760).

A 2026 pharmacovigilance analysis examined spontaneous reports of dysaesthesia in the VigiBase safety database and in French pharmacovigilance case narratives, with a literature review; its abstract gives no report count, its report analysis covered approved GLP-1 receptor agonists and tirzepatide rather than retatrutide, and spontaneous reports cannot give a frequency or prove cause (Laroche et al., European Journal of Clinical Pharmacology, 2026). On the kidneys, a post hoc analysis of the two Phase 2 trials (281 adults with type 2 diabetes and 338 with overweight or obesity), run after the trials by authors including developer employees, found eGFR (a kidney filtering measure) unchanged in people with type 2 diabetes and higher in people with obesity (Heerspink et al., Kidney International Reports, 2025). The hair-loss question is covered on the study findings page.

How many people stopped retatrutide trials because of side effects?

In the 80-week TRIUMPH-2 trial of 1,152 adults with type 2 diabetes, permanent discontinuation because of an adverse event or death was 4%, 12% and 8% across the three retatrutide arms against 5% on placebo, a result for that developer-funded trial only (Bellido et al., The Lancet, 2026). In TRANSCEND-T2D-1, a 40-week trial of 537 adults with type 2 diabetes, discontinuations because of adverse events were 2% to 5% with retatrutide and 0% with placebo, counted differently from TRIUMPH-2 and so not comparable with it (Bajaj et al., The Lancet, 2026). The Phase 2 obesity registry lists an adverse event as the reason for leaving the study for 6 retatrutide participants and none on placebo, in a small developer-funded trial of 338 adults that cannot show how often rarer events lead to stopping (ClinicalTrials.gov NCT04881760).

The counts differ between trials because the trials differ in length, population and the rules for counting. TRIUMPH-2 combined adverse events and deaths into one measure, and TRANSCEND-T2D-1 counted adverse events alone (Bellido et al., The Lancet, 2026; Bajaj et al., The Lancet, 2026). A percentage only means something while it stays attached to the trial that produced it.

What have Australian authorities reported about products sold as retatrutide?

Australian authorities have issued two warnings about products sold as retatrutide. On 14 September 2026 the TGA reported that one consumer had uncontrollable vomiting that tore the oesophagus and needed hospital care, and that laboratory testing of the unmarked vial found undeclared semaglutide at about eight times the level in semaglutide products on the Australian Register of Therapeutic Goods, and no retatrutide, a report about one person and one sample that does not show how common such events are (TGA safety alert, 14 September 2026). On 19 June 2026 the Victorian Chief Health Officer reported six cases of acute liver injury since January 2026 in people who had used products labelled retatrutide, possibly linked to a contaminant, in an alert about case reports in which the cause was not established (Victorian health alert, 19 June 2026).

A 2026 laboratory study tested three products sold as retatrutide in Australia. All three matched the expected molecular weight, but the measured peptide content ranged from 51% to 190% of the labelled amount, a three-product sample that cannot show what the wider market holds (Piatkowski et al., Drug and Alcohol Review, 2026). A 2026 case report describes one woman in her mid-20s with five days of nausea and vomiting that resolved within a week after exposure to an unverified product reported to contain retatrutide, with probable causality on the Naranjo scale, and a single case cannot show how common this is (Buzzi et al., BMJ Case Reports, 2026).

These records describe specific products and specific people. They cannot show how common such harms are, and they are not trial data. Retatrutide's legal status in Australia sets out the TGA statements with their dates.

Which clinical trial paper reports retatrutide's half-life?

The Phase 1b trial of 72 adults with type 2 diabetes reports retatrutide's half-life as approximately six days and its pharmacokinetics as dose proportional, in a small early-phase trial funded by the developer that describes that group only (Urva et al., The Lancet, 26 November 2022). The registry lists the trial as enrolling those 72 adults at four US centres from 18 December 2019 to 28 December 2020 (ClinicalTrials.gov NCT04143802). The first-in-human study in Cell Metabolism reports a separate pharmacokinetic profile in 45 healthy adults, from a small single-exposure study that describes those adults only (Coskun et al., 2022).

Pharmacokinetics means what the body does to a compound over time. The pharmacokinetics page sets out the half-life range, the time to peak concentration and the gaps in the record, such as the absence of a published human metabolism study among the sources checked.

Do these side-effect records apply to research-use retatrutide?

No. The trial figures on this page come from trial drug product given to enrolled participants who were screened and monitored by trial staff (Bellido et al., The Lancet, 2026; Jastreboff et al., NEJM, 2023), and the regulator and case-report records describe products from outside trials whose contents were unverified at the time of exposure, although the TGA later tested one of them in a laboratory (TGA safety alert, 14 September 2026). Research-use retatrutide is a laboratory compound. Research material is not a medicine, is not a substitute for one, and is not for human or animal use. No side-effect record here describes it, and these records cannot establish the effects of other products.

What exists for laboratory work is reference material with paperwork. This site's retatrutide reference material listing is freeze-dried laboratory stock. Available reports cover historical samples, and matching current certification is unverified. The retatrutide research guide covers the compound itself.