Home > Articles > Retatrutide side effects: what the trial reports list
Prepared by: Research Desk
Prepared by: Research Desk. Sources are linked for verification.
Status: Investigational. Retatrutide is not approved by the FDA, and we know of no approval by any other major regulator. The FDA states it "cannot be used in compounding under federal law" and has "not been found safe and effective for any condition" [1]. Our approval status page covers the full regulatory picture.
People searching "retatrutide side effects" often find forum posts, screenshots and secondhand summaries. This page relies only on published trial reports, official trial records and peer-reviewed reviews. It describes what those studies measured and reported. It makes no predictions about any individual, and it gives no guidance on using the drug.
Our trial-by-trial guide covers the efficacy results and the overall evidence for each study in more depth.
Side effects vs adverse events: what trials actually record
Trial reports rarely use the phrase "side effects". They record adverse events. An adverse event is any unwanted medical occurrence during the study, whether or not the drug caused it. A headache during a trial counts as an adverse event even if it has nothing to do with the study drug.
That is why the placebo group matters. In a randomised, double-blind trial, participants are assigned by chance to the study drug or to an inactive comparator. Neither the participants nor the study staff know who received which. If nausea appears in a much larger share of the drug groups than of the placebo group, that gap is the signal. The raw percentage on its own is not.
Trial reports usually track four things:
Frequency. The share of participants in each group who reported a given event.
Severity. Usually graded mild, moderate or severe.
Serious adverse events. Events that meet a regulatory definition, such as those leading to hospital admission.
Discontinuation. The share of participants who stopped the study drug because of an adverse event.
Phase 2 obesity trial (NEJM, 2023)
The phase 2 obesity trial ran for 48 weeks. It randomised 338 adults who had obesity, or who had overweight plus at least one weight-related condition. It compared several retatrutide groups with placebo [2].
The report described these safety findings [2]:
Gastrointestinal events were the most common. These were mainly nausea, diarrhoea, vomiting and constipation. Most were mild to moderate in severity, and they were dose-related.
Heart rate increased. Heart rate rose in a dose-related way. It peaked at around 24 weeks and declined afterwards.
Discontinuation due to adverse events ranged from 6% to 16% across the retatrutide groups, compared with 0% in the placebo group.
This was a mid-sized phase 2 human study, designed to inform the design of phase 3. It was not designed to detect rare events. A 48-week study of a few hundred people cannot rule out uncommon or long-term harms.
Phase 2 type 2 diabetes trial (Lancet, 2023)
A separate phase 2 trial was conducted in the USA. It was randomised and double-blind, and it enrolled 281 adults with type 2 diabetes for 36 weeks [3]. It had two comparators:
a placebo;
an active comparator, dulaglutide, which is an established GLP-1 receptor agonist.
As in the obesity trial, gastrointestinal adverse events were the most frequently reported category, and most were mild to moderate [3].
The active comparator adds useful context. It shows how tolerability in the retatrutide groups compared with a drug class already in wide use, not only with an inactive comparator.
Liver-fat study (Nature Medicine, 2024)
A randomised phase 2a study in humans reported changes in liver fat in participants with metabolic dysfunction-associated steatotic liver disease (MASLD) [4]. Its main purpose was to measure liver fat, not to characterise the safety profile, and it was smaller than the phase 3 programme.
We list it here because it is often cited alongside discussions of side effects. Readers should know what a study was built to measure before drawing safety conclusions from it.
Phase 3: TRIUMPH and TRANSCEND reports
The phase 3 programme is much larger than phase 2, so its safety sections carry more weight. Published or registered phase 3 studies include:
Study | Population (per title or record) | Design | Source |
|---|---|---|---|
TRIUMPH-1 | Adults with obesity or overweight | Phase 3, placebo-controlled | [5][8] |
TRIUMPH-2 | Adults with obesity and type 2 diabetes | Phase 3, double-blind, parallel-group, randomised, placebo-controlled | [6] |
TRANSCEND-T2D-1 | Type 2 diabetes with inadequate glycaemic control on diet and exercise | Phase 3, double-blind, randomised | [7] |
TRIUMPH-3 | Obesity with cardiovascular disease | Phase 3, registered | [9] |
TRIUMPH-4 | Obesity with knee osteoarthritis | Phase 3, registered | [10] |
TRIUMPH-5 | Head-to-head comparison with tirzepatide | Phase 3, registered | [11] |
Phase 3 safety reporting usually adds what phase 2 cannot provide:
larger denominators;
longer follow-up;
adjudicated events for specific categories;
subgroup breakdowns.
The published TRIUMPH-1, TRIUMPH-2 and TRANSCEND-T2D-1 papers present their findings by assigned group, and the TRANSCEND-T2D-1 report names safety alongside efficacy in its title [5][6][7]. We do not reproduce their tables here. Readers who want exact percentages are best served by the papers themselves.
The ClinicalTrials.gov records list the prespecified outcome measures for each study. Once results are posted, they also carry the results summaries [8][9][10][11].
How the pattern compares with the wider drug class
Gastrointestinal adverse events are not unique to retatrutide. A 2025 systematic review of randomised trials of GLP-1 receptor agonists for weight loss in adults without diabetes assessed both efficacy and safety, and gastrointestinal adverse events featured prominently among its tolerability findings [12]. A broader 2025 systematic review examined emerging obesity pharmacotherapies, a category that includes newer multi-receptor agonists such as retatrutide [13].
Secondary literature needs some caution, because some reviews use enthusiastic framing. For example, a 2025 review in Biomolecules called retatrutide a "game changer" in its title [14]. A review summarises other studies. It does not generate new safety data, and a title is not evidence. When a review makes a claim about side effects, it is worth checking against the primary trial report that the review cites.
Trial findings vs products sold online
Every number above comes from controlled studies. Those studies used a manufacturer-supplied investigational product of known identity and purity. Participants were monitored under a registered study plan.
None of that applies to substances sold online under the retatrutide name. The FDA says retatrutide cannot be compounded and has not been found safe and effective for any condition [1]. The same FDA page describes warnings issued to companies that marketed it [1].
A product of unknown identity has no published adverse event profile at all. The trial data simply do not describe it.
Reading a safety table: five checks
Compare against placebo, not against zero.
Check the denominator. Note how many people were in each group, and for how long.
Separate severity grades. "Any nausea" and "severe nausea" are different findings.
Look at discontinuations. They show which events were disruptive enough to end participation.
Note what the trial could not detect. Rare and long-term events need larger, longer studies.
Further reading on trial methods
The checklist above draws on general principles of trial design and statistics. Readers who want to go deeper can choose from many well-regarded books on these subjects.
A few neutral criteria separate useful titles in this category from weak ones:
Edition date. Reporting standards and statistical practice change over time. A recent edition is more likely to reflect current conventions for reporting harms.
Level. Some titles assume calculus or prior statistics training, while others are written for general readers. The preface or table of contents usually makes the level clear.
Coverage of harms. Many methods books concentrate on efficacy endpoints. The strongest titles include chapters on adverse event reporting, multiplicity and interpreting rare events.
Worked examples. Books that walk through real published tables are easier to apply than purely theoretical texts.
Format and price transparency. Paperback, hardback and ebook prices can differ widely. Independent bookseller platforms show the list price up front, and buying through them supports local bookshops.
A good methods book makes any published safety table easier to interpret, whatever the subject of the study. That makes it a long-lasting reference for anyone who follows trial results closely.
Frequently asked questions
What is the most common retatrutide side effect reported in trials?
Gastrointestinal adverse events were the most frequently reported category in the phase 2 obesity and type 2 diabetes trials [2][3]. These were mainly nausea, diarrhoea, vomiting and constipation, and most were graded mild to moderate. Gastrointestinal events are also a prominent tolerability finding across the wider GLP-1 receptor agonist class [12].
Did retatrutide trials report heart rate changes?
Yes. The phase 2 obesity trial reported dose-related increases in heart rate that peaked at around 24 weeks and declined afterwards [2]. Larger and longer phase 3 studies, including TRIUMPH-3 in people with cardiovascular disease, are positioned to describe cardiovascular findings more fully [9].
Do trial side-effect findings apply to retatrutide sold online?
No. Trial data describe a manufacturer-supplied investigational product used under a registered study plan, while the FDA states that retatrutide cannot be compounded and has not been found safe and effective for any condition [1]. Our approval status page covers legal status, and our About page explains our sourcing standards.
Last updated: 19 October 2026.
Related on this site
Is retatrutide FDA approved? Legal status and approval timeline
Retatrutide: mechanism, trial findings and side effects explained
How to read retatrutide trial results: endpoints, placebo, dropouts
Books about clinical trials: a reading list for following research
Retatrutide vs tirzepatide: how the trial designs and data compare
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