Retatrutide: Side Effects, Results, Legality and More, Answered

The published trials were funded by Eli Lilly ^1,6. The phase 3 programmes are called TRIUMPH (obesity, including people with knee osteoarthritis or sleep apnea) and TRANSCEND (type 2 diabetes) ^3,4,5,11.

All of this work is in humans enrolled in controlled trials. Material sold outside those trials is not the trial product. Amiravo's retatrutide entry lists every trial and registry record.

In cell studies, its activity at the glucagon and GLP-1 receptors was roughly balanced, with relatively more activity at the GIP receptor ⁶. The energy-expenditure finding comes from mice, not humans ⁶.

In humans, early studies showed a half-life of about 6 days, which supported once-weekly injections ¹⁰. "GLP-3" is not a recognised drug class. An FDA warning letter cites a product marketed as "GLP-3R (retatrutide)" ¹⁷.

For the background on single, dual and triple agonists, see GLP-1, GIP and glucagon: from single to dual to triple agonists.

The 2026 phase 3 publications describe retatrutide as an agent under investigation ^3,4,5. The TRIUMPH-1 and TRIUMPH-3 registry records list the trials as completed ^8,16.

Any approval would follow an FDA review of a company application. The company's stated filing plans are covered in Amiravo's news report, Retatrutide: Lilly reports TRIUMPH-2 and TRIUMPH-3 phase 3 results.

These are group averages from monitored trials. Individual stories and photos are not trial evidence.

TRIUMPH-1 also reported larger improvements than placebo in knee-pain scores and in the apnea-hypopnea index in its osteoarthritis and sleep-apnea subgroups ³. A 2026 report of sleep-apnea substudies nested within TRIUMPH-1 and TRIUMPH-2 reported the same direction of effect ¹¹.

Trial results describe averages at set time points, not what one person will see ^1,3,5. No study has examined why some people report that retatrutide "stopped working" or "is not working".

The longest published treatment period is 80 weeks ^3,4. The TRIUMPH-1 registry lists an optional extension to week 104, without published results in the sources reviewed ⁸.

In the phase 2 diabetes trial, HbA1c change at 24 weeks ranged from -0.43 to -2.02 percentage points across doses ². That compares with -0.01 with placebo and -1.41 with dulaglutide ². Body weight fell by up to 16.94% at 36 weeks ².

TRANSCEND-T2D-1 enrolled adults managing diabetes with diet and exercise alone ⁵. TRIUMPH-2 studied adults with both obesity and type 2 diabetes ⁴.

In the phase 2 obesity trial, some groups started at 2 mg and stepped up to their target dose ^1,7. The phase 3 abstracts do not describe the step-up schedules ^3,4,5.

Every trial used fixed doses, not doses by body weight ^1,3. Charts "by weight" and dose calculators found online do not come from the trials. The full list of study arms is on Retatrutide dosage in human studies.

The phase 1b, phase 2 and phase 3 trials all used subcutaneous injection ^1,3,10. Peptides are usually broken down in the gut, which is why most are injected; see Why most peptides are injected.

The trial abstracts describe once-weekly subcutaneous injections and do not mention time of day or food ^3,4. Approved drugs in the same family carry these details on their labels; retatrutide does not have one.

Source: TRIUMPH-2 ⁴. In the phase 2 obesity trial, nausea affected 45% of the highest-dose group versus 11% with placebo ⁷. Heart-rate increases peaked at 24 weeks and declined afterwards ¹.

A 2026 review notes that skin-sensitivity events were also reported in phase 2, at 7% versus 1% ¹⁵. The sources reviewed do not report side effects separately for women and men.

Deaths occurred in TRIUMPH-2 and TRANSCEND-T2D-1; investigators judged all of them unrelated to the study drug ^4,5. Discontinuation for adverse events was 2% to 5% versus 0% in TRANSCEND-T2D-1 ⁵.

FDA warns that unapproved incretin products labeled "for research purposes" are of unknown quality ¹². Trial safety data describe the manufacturer's product given under medical supervision, not research-market vials.

The TRIUMPH-1 abstract lists gastrointestinal events as the most common ³. Hypotension and dysesthesia were reported in TRIUMPH-2 ⁴. Absence from an abstract does not mean an event never occurred.

For comparison, the Zepbound (tirzepatide) label reports hair loss in 4% to 5% versus 1% with placebo ¹³. It reports fatigue in 5% to 7% versus 3% ¹³. Those figures apply to tirzepatide, not retatrutide.

The exclusion criteria are listed in the TRIUMPH-1 registry record ⁸. The tirzepatide label's boxed warning describes thyroid C-cell tumors in rats and states that the human relevance is unknown ¹³.

Retatrutide has no label, so no equivalent warning or long-term safety review exists for it.

FDA has warned telehealth companies, ingredient distributors and outsourcing facilities over retatrutide ¹². These actions are summarised in FDA in 2026: telehealth GLP-1 letters and a line on retatrutide. One FDA warning letter cites a product marketed as "GLP-3R (retatrutide)" ¹⁷. Related news: Lilly files six lawsuits against US retatrutide sellers.

The wider framework is explained in Peptide legality in the United States. If you are judging a research material, the starting point is its certificate of analysis; see Reading a certificate of analysis.

S0 covers any pharmacological substance not addressed by any subsequent section of the List and with no current approval for human therapeutic use ⁹. Retatrutide has no such approval ¹². How anti-doping rules treat peptides is covered in Peptides and sport.

FDA states that retatrutide is not part of any approved drug, so no "how supplied and storage" section exists for it ¹². General handling principles are in Storage and handling basics.

In separate trials, TRIUMPH-1 reported -17.6% to -25.0% at 80 weeks ³ and SURMOUNT-1 reported -15.0% to -20.9% for tirzepatide at 72 weeks ¹⁸. Different designs and lengths make direct comparison unreliable.

The full side-by-side is on Tirzepatide vs retatrutide.

The Ozempic label describes semaglutide as a selective GLP-1 receptor agonist ¹⁴. Retatrutide's receptor profile is described in its trial reports ^3,6.

See Semaglutide vs retatrutide for the full comparison.

The tirzepatide label states that combining it with any other GLP-1 receptor agonist is not recommended ¹³. Retatrutide is a GLP-1 receptor agonist ³.

Amiravo's combination pages list what is known and unknown: cagrilintide + retatrutide, retatrutide + MOTS-c and retatrutide + CJC-1295 + ipamorelin. Muscle-preservation claims for these pairings are untested.