Retatrutide vs Tirzepatide: What's the Difference?
Last updated 13 June 2026
Quick answer
| Retatrutide | Tirzepatide | |
|---|---|---|
| Signals used | Three (GLP-1, GIP, glucagon) | Two (GLP-1, GIP) |
| Made by | Eli Lilly | Eli Lilly |
| Trial stage (2026) | Phase 3 ongoing | Approved medicine |
| Brand names | Retaklik (research) | Mounjaro, Zepbound |
| Top trial weight result | Up to ~71 lb avg (Phase 3) | Up to ~22% (SURMOUNT) |
| UK status | Research use only | Prescription medicine |
What each one is
Both are made by Eli Lilly. Tirzepatide is already an approved medicine in the UK and many other places, sold as Mounjaro. Retatrutide is newer and still in trials. Learn the basics on our retatrutide guide.
How they work (simple)
Tirzepatide copies two gut signals. GLP-1 tells your brain you are full. GIP helps the body handle sugar. Retatrutide copies those two and adds a third, glucagon, which helps the body burn stored energy. More signals working together is the headline difference. See how retatrutide works.
What the trials found
Tirzepatide's SURMOUNT trials showed strong weight loss and led to its approval. Retatrutide's Phase 2 study showed up to 17.5% weight loss in 24 weeks, and Phase 3 trials in 2025–2026 showed even larger results. The catch: these are different trials with different people and rules. So the numbers hint that retatrutide may be stronger, but they are not a clean head-to-head.
Which is "stronger"?
On the trial numbers so far, retatrutide leads on weight change. But "promising in research" is not the same as "proven better for you". Tirzepatide has the big advantage of being an approved, regulated medicine you can actually be prescribed.
UK status of each
Tirzepatide is a prescription medicine. Retatrutide is not approved and is sold only as a research chemical. If you are comparing research suppliers, read our where-to-buy guide first.
If the triple-agonist edge is what interests you, see our guide to buy retatrutide UK safely.
Looking at suppliers?
Compare UK research suppliersCommon questions
Is retatrutide stronger than tirzepatide?+
In separate trials, retatrutide showed larger average weight loss than tirzepatide. They have not been tested head-to-head in one big trial yet, so this is a careful comparison based on different studies, not a final answer.
Is tirzepatide the same as Mounjaro?+
Yes. Tirzepatide is the drug name. Mounjaro and Zepbound are brand names for it.
What is the main difference?+
Tirzepatide switches on two signals: GLP-1 and GIP. Retatrutide adds a third, glucagon. That extra signal is the core difference and may help the body burn more energy.
Which one can I buy in the UK?+
Tirzepatide is a prescription medicine. Retatrutide is not approved and is sold only as a research chemical for laboratory use.