Home / Compare / Retatrutide vs tirzepatide
Retatrutide vs tirzepatide
Retatrutide · Mounjaro (tirzepatide)
The short answer
One of these is a medicine and one is not, yet.
Retatrutide has produced the largest weight-reduction figures reported in this class. It is also not approved in any country, so nobody independent has weighed its benefits against its risks. Tirzepatide is licensed in the UK, available on prescription, and has years of real-world use behind it.
Comparing a phase 3 candidate to a licensed medicine on effect size alone is how people end up buying vials from strangers.
Everything below goes into the detail, with sources on each record.
01Side by side
| Retatrutide | Mounjaro (tirzepatide) | |
|---|---|---|
| UK status | Not licensed anywhere | MHRA licensed |
| Availability | Clinical trials only | Prescription only |
| Evidence base | Phase 3 ongoing | Human RCT, phase 3 |
| Controlled drug | No | No |
| Drug class | Triple receptor agonist | Dual GIP and GLP-1 receptor agonist |
02What is the same
- Both are peptides given as weekly injections.
- Both act on GLP-1 and GIP receptors. Retatrutide adds a third.
- Both from Eli Lilly.
- Both reduce appetite, and both would be expected to show weight regain after stopping.
03What actually differs
| Retatrutide | Tirzepatide | |
|---|---|---|
| Receptors | GLP-1, GIP and glucagon | GLP-1 and GIP |
| Approved anywhere? | No | Yes, including the UK |
| How to obtain lawfully | Clinical trial only | Prescription |
| Safety profile | Not established by any regulator | SPC, plus additional MHRA monitoring |
| Yellow Card cover | No | Yes |
The third receptor is glucagon, which raises blood glucose by design while also increasing energy expenditure. Whether that trade works out safely over years is exactly what phase 3 exists to determine, and it has not reported fully.
04What the evidence says
Retatrutide's phase 2 results generated enormous attention for weight reductions beyond anything previously reported. The phase 3 TRIUMPH programme is ongoing, with regulatory submission publicly discussed for late 2026 and any UK licence later than that.
There is no head-to-head trial against tirzepatide. Every comparison you have read lines up separate trials with different populations, durations and designs, which is exactly the unreliable method that made CagriSema look competitive until REDEFINE 4 tested it directly against tirzepatide and it lost.
CagriSema was widely expected to beat tirzepatide on the strength of separate-trial comparisons. When they were compared head to head, tirzepatide won and CagriSema missed its non-inferiority threshold. Cross-trial comparisons are not evidence, and this class has already produced a worked example.
05Which suits whom
If you are considering retatrutide, there are two honest options.
- Join a trial. Be Part of Research lists UK studies. You get the drug, monitoring by clinicians, and the product is what it says it is.
- Use something licensed in the meantime. Tirzepatide is available, assessed and monitored.
The third option, buying it online, means an unlicensed injectable of unverifiable identity, purity and concentration, with no monitoring and no route to report harm. The MHRA seized over 2,000 unlicensed weight-loss pens along with raw manufacturing ingredients in October 2025, which tells you what part of that supply chain actually looks like.
06Getting either in the UK
Retatrutide has no marketing authorisation anywhere. It cannot be lawfully supplied for human use in the UK, and the only lawful route to receiving it is an authorised clinical trial.
Tirzepatide is licensed and available on NHS prescription under criteria, or privately through registered pharmacies.
07The honest bottom line
Retatrutide may well turn out to be the most effective drug in this class. Nobody knows yet, because the trials that would establish it, and establish its risks, have not finished.
Waiting for a licensed medicine is not a compromise. It is the difference between a product somebody has verified and a vial somebody has posted you.
08Common questions
Is retatrutide better than Mounjaro?
Unknown. Retatrutide's phase 2 figures were larger, but there is no head-to-head trial, and cross-trial comparisons are unreliable. CagriSema looked competitive on that basis until a direct comparison against tirzepatide went the other way.
Can I buy retatrutide in the UK?
Not lawfully. It has no marketing authorisation anywhere, so supplying it for human use is prohibited under the Human Medicines Regulations 2012. It is sold on the grey market as a research chemical.
When will retatrutide be available?
Regulatory submission has been publicly discussed for late 2026, with any UK licence and NHS decision later than that. Those are estimates from company statements, not commitments.
What does the third receptor actually add?
Glucagon receptor activation, which raises blood glucose but also increases energy expenditure. The bet is that the GLP-1 component offsets the glucose effect. Whether that holds safely over years is what phase 3 is for.
Full record
Retatrutide
Still in trials. Widely sold on the grey market, which is illegal and unverifiable.
Full record
Tirzepatide
The other licensed drug in this space, and the first approved anywhere to act on two hormone receptors at once.
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