Retatrutide: what the trials of the new triple-hormone jab show
Retatrutide is a new weekly weight-loss injection that has produced some of the largest weight losses seen in medicine trials. Here's what the research shows, and why you shouldn't buy it online.
Medically reviewed by Dr LJ Ncube, MBChB · Updated November 2026
- Retatrutide copies three hormones, one more than Mounjaro
- In the main phase 3 trial, people lost about a quarter of their body weight on average over 80 weeks
- It isn't approved by regulators yet (as of November 2026)
- Products sold online as retatrutide are unregulated and may not contain what they claim
How it works
Semaglutide (Ozempic, Wegovy) copies one gut hormone, GLP-1. Tirzepatide (Mounjaro) copies two, GLP-1 and GIP. Retatrutide copies three: GLP-1, GIP and glucagon. The first two reduce appetite. Glucagon is thought to increase the energy your body uses and help clear fat from the liver.
What the trials show
Show as a table
| Retatrutide 12 mg | 25% |
| Retatrutide 9 mg | 23.7% |
| Retatrutide 4 mg | 17.6% |
| Placebo | 3.9% |
Source: Jastreboff AM, et al. N Engl J Med. 2026.
| Trial | Who took part | Average weight loss |
|---|---|---|
| Phase 2 (2023) | 338 adults with obesity | About 24% at the highest dose, after 48 weeks |
| TRIUMPH-1, phase 3 (2026) | 2,339 adults with obesity, without diabetes | About 25% at the highest dose, after 80 weeks (about 4% with placebo) |
| TRIUMPH-2, phase 3 (2026) | 1,152 adults with obesity and type 2 diabetes | About 19% at the highest dose, after 80 weeks (about 5% with placebo) |
In TRIUMPH-1, people with knee arthritis also had less knee pain, and people with sleep apnoea had fewer breathing pauses at night.
These are averages from tightly run trials with regular check-ups. They're also funded by the manufacturer, which is normal for medicine trials, but worth knowing.
Side effects
The most common side effects were stomach-related, such as nausea, diarrhoea and vomiting, and were more common at higher doses. In the TRIUMPH-2 trial, about a third of people on the two higher doses had diarrhoea. In the earlier trial, heart rate went up a little, peaking around 6 months and then settling. Long-term safety is still being studied.
Can I get it?
Not as an approved medicine yet. As of November 2026, retatrutide hasn't been approved by the US FDA or other major regulators. In the US, a small compassionate-use programme exists for people with severe obesity who haven't responded to other treatment.
Why not buy it online?
- Anything sold now as retatrutide hasn't come from an approved, checked supply
- The dose, purity and even the contents of the vial are unknown
- Injecting unsterile products can cause serious infections
- There's no doctor checking for side effects or adjusting your dose
Approved medicines such as semaglutide and tirzepatide already produce large weight losses for many people. A doctor can tell you whether one is right for you now.
Answer a few questions online and our doctor will reply on WhatsApp, usually within 24 hours.
Common questions
Is retatrutide better than Mounjaro?
In separate trials, average weight loss was higher with retatrutide, but the two haven't been compared directly in a published head-to-head trial yet.
When will retatrutide be available?
Nobody can say for sure. It depends on regulators reviewing the evidence, which usually takes about a year after an application is submitted.
Is retatrutide a peptide?
Yes, like semaglutide and tirzepatide. Unlike unregulated research peptides, it has been tested in large clinical trials.
Related
Sources
We base our guides on peer-reviewed research and guidance from health authorities. Where studies disagree or evidence is limited, we say so.
- Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med. 2023. PubMed
- Jastreboff AM, et al. Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1). N Engl J Med. 2026. PubMed
- Bellido V, et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2). Lancet. 2026. PubMed
- Brown C. Retatrutide: obesity drug opens to compassionate use in US. BMJ. 2026. PubMed
This guide is general information, not advice for your situation. Speak to a doctor before starting or changing any medicine.
