Retatrutide vs Mounjaro vs Wegovy
One of these medicines does not exist yet as a product. The other two are available in the UK right now. Here is the honest comparison — numbers, caveats, and what it means if you are choosing treatment today.
Independently written · Last reviewed: · editorial policy
Key facts in 30 seconds
- Best trial averages: Wegovy ≈14.9% (STEP 1, 68 weeks), Mounjaro ≈20.9% (SURMOUNT-1, 72 weeks), retatrutide 28.3% (TRIUMPH-1, 80 weeks) — different trials, not head-to-head.
- “Retatrutide is a third more effective than Mounjaro” is arithmetic, not evidence; the TRIUMPH-5 head-to-head settles it in late 2026/2027.
- Mounjaro and Wegovy are MHRA-authorised now, roughly £94–£230 and £100–£170 per month privately through GPhC-registered pharmacies.
- Retatrutide has no approval, no price and no legal supply — a reason to check back in 2028, not to pay anyone today.
- Whichever medicine: prescription-only supply must go through a GPhC-registered pharmacy after a genuine clinical consultation.
Side by side
| Wegovy (semaglutide) | Mounjaro (tirzepatide) | Retatrutide (LY3437943) | |
|---|---|---|---|
| Mechanism | GLP-1 agonist | GIP + GLP-1 agonist | GIP + GLP-1 + glucagon agonist |
| Best trial average | ≈14.9% weight loss (STEP 1, 68 wks) | ≈20.9% (SURMOUNT-1, 72 wks) | 28.3% (TRIUMPH-1, 80 wks) |
| Status in the UK (Sept 2026) | MHRA-authorised; private + limited NHS | MHRA-authorised; private + phased NHS | Not authorised anywhere; trials only |
| Typical private cost | From roughly £100–£170/month depending on dose and pharmacy | From roughly £94–£230/month depending on dose and pharmacy; tracked at monj.co.uk | No price exists — none has been announced by anyone |
| Common side effects | Nausea, diarrhoea, vomiting, constipation | Same class pattern | Same class pattern, dose-related; heart-rate rise under study |
| Head-to-head evidence | vs tirzepatide: tirzepatide ahead (SURMOUNT-5) | — | vs tirzepatide: TRIUMPH-5, expected late 2026/2027 |
The number everyone quotes — and why to hold it lightly
“Retatrutide is a third more effective than Mounjaro” comes from dividing 28.3% by 20.9%. It is arithmetic, not evidence. TRIUMPH-1 ran 80 weeks against SURMOUNT-1's 72, in different populations with different dropout rates and different lifestyle support. The scientifically valid comparison — randomised, same protocol, same population — is TRIUMPH-5, retatrutide versus tirzepatide head-to-head, whose results are expected around late 2026 or 2027. Until then the honest statement is: retatrutide's trial numbers are the highest ever reported for this class, very likely meaningfully ahead of tirzepatide, with the size of the edge unproven.
What the difference might actually mean
Even if the edge holds, a few points of extra average weight loss matter differently for different people. For someone with severe obesity and multiple conditions, the larger effect may be genuinely important. For someone closer to their goal, an available, well-understood, cheaper medicine they can start this week often beats a marginally stronger one that is years away. Side-effect burden is also real: the bigger the effect, the more pronounced the gastrointestinal titration tends to be, and retatrutide's 12 mg maintenance dose had more discontinuations than lower doses.
If you are choosing treatment in the UK now
- Mounjaro (tirzepatide) currently offers the strongest approved effect. Our sister site monj.co.uk independently tracks UK pharmacy prices and verifies GPhC registration — delivery-inclusive prices start around £94/month at the starter dose.
- Wegovy (semaglutide) remains a solid option, particularly where supply or price suits, and oral GLP-1 options are beginning to widen the field.
- Retatrutide is a reason to check back in 2028, not a reason to hand money to a website today. There is no legal retatrutide for sale — anywhere.
Whichever medicine: the same UK safety rules
- Prescription-only medicines must come through a GPhC-registered pharmacy, after a genuine clinical consultation.
- Check the pharmacy yourself on the official GPhC register.
- Confirm the full delivered price — prescription, consultation, delivery and any extras — before paying.
- Be wary of sellers who need no consultation, or who advertise unapproved medicines by name.
Cite this page
Johnson N. Yezz — independent UK retatrutide information. Medstack Ltd, 10 September 2026. https://yezz.co.uk/retatrutide-vs-mounjaro-vs-wegovy
Sources
Every factual claim on this page traces to one of these primary sources. We link out so you can check the original.
- 1.Trial result summaries and cross-trial context — TRIUMPH and SURMOUNT/STEP headline figures
- 2.TRIUMPH-1 vs SURMOUNT-1 vs STEP 1 comparison notes — cross-trial caveats (a research-chemical seller — we cite only its trial data summary)
- 3.TRIUMPH-5 head-to-head registration — expected completion, December 2026
- 4.monj.co.uk — independent UK Mounjaro price tracking — live GPhC-verified pharmacy prices used for the Mounjaro cost range above
- 5.GPhC pharmacy register — official register for verifying any UK pharmacy