Retatrutide in the UK: TRIUMPH-1 Phase 3 results, honest timeline and what to do right now (2026)

  • By Amina Mughal

Published: Thursday, June 18, 2026

TL;DR — key facts

Retatrutide is Eli Lilly's triple-agonist injection targeting GLP-1, GIP and glucagon simultaneously — the first of its class to reach Phase 3. TRIUMPH-1 (published May 2026): 28.3% average weight loss at 80 weeks on 12mg — 45.3% of participants achieved ≥30% loss, matching bariatric surgery outcomes. Not approved by the MHRA. Cannot be legally prescribed in the UK in 2026. 

Realistic UK private availability: late 2027 to mid-2028. NHS via NICE: 2029 at earliest.

28.3%

Average weight loss at 80 weeks (12mg, TRIUMPH-1)

45.3%

Participants achieving ≥30% loss — bariatric surgery level

2027–28

Earliest realistic UK private availability
Title

What is retatrutide and why is everyone talking about it?

Developed by Eli Lilly (makers of Mounjaro) under code LY3437943, retatrutide is the world's first triple hormone receptor agonist to reach Phase 3. Semaglutide pulls one lever, tirzepatide pulls two — retatrutide pulls three, adding glucagon receptor activation that increases energy expenditure, not just appetite suppression. This is why the weight loss numbers are in a category of their own... 

 

Important: what is sold online as "retatrutide pens" is not Eli Lilly's compound. These are unregulated research chemicals.

Title

The TRIUMPH Phase 3 programme: what the data actually shows

Clinical trial data Average body weight loss — retatrutide vs approved treatments TRIUMPH-1 Phase 3 at 80 weeks (Eli Lilly, May 2026)
Retatrutide (investigational — not approved)
Licensed in UK
Placebo
45.3% of participants on retatrutide 12mg achieved ≥30% weight loss — a level historically associated only with bariatric surgery. No direct head-to-head trial has been conducted.
Sources: TRIUMPH-1 Phase 3 NCT05929066 (Eli Lilly, May 2026) · Mounjaro: SURMOUNT-1 72-week data · Wegovy: STEP 1 68-week data. Retatrutide is not approved by the MHRA.

Mechanism comparison

Treatment comparison

Retatrutide vs approved UK weight loss treatments

Drug How it works Weight loss Women UK status
Retatrutide 12mg · Eli Lilly Triple agonist — GLP-1, GIP + glucagon. Boosts energy burn, not just appetite. 28.3% at 80 wks 30.3% at 104 wks ✓ Yes Phase 3Not MHRA approved
Mounjaro 15mg · Tirzepatide Dual agonist — GLP-1 + GIP. Best currently approved option. ~22.5% at 72 wks ✓ Yes Licensed
Wegovy 7.2mg Semaglutide · New dose GLP-1 mono agonist. Highest licensed semaglutide dose globally. ~18.7% at 72 wks ✓ Yes Jan 2026
Wegovy 2.4mg Semaglutide · Standard GLP-1 mono agonist. First widely available weight-loss semaglutide. ~15% at 68 wks ✓ Yes Licensed
Orlistat Xenical / Alli Lipase inhibitor — blocks dietary fat absorption in the gut. ~8% at 52 wks ✓ Yes OTC licensed
Retatrutide 12mg Phase 3
How it works
Triple agonist — GLP-1, GIP + glucagon
Weight loss
28.3% at 80 wks · 30.3% at 104 wks
Women
✓ Yes
UK status
Not approved — Phase 3
Mounjaro 15mg Licensed
How it works
Dual agonist — GLP-1 + GIP
Weight loss
~22.5% at 72 weeks
Women
✓ Yes
UK status
Licensed
Wegovy 7.2mg Jan 2026
How it works
GLP-1 mono agonist — new higher dose
Weight loss
~18.7% at 72 weeks
Women
✓ Yes
UK status
Licensed
Wegovy 2.4mg Licensed
How it works
GLP-1 mono agonist — standard dose
Weight loss
~15% at 68 weeks
Women
✓ Yes
UK status
Licensed
Orlistat Licensed OTC
How it works
Lipase inhibitor — blocks fat absorption
Weight loss
~8% at 52 weeks
Women
✓ Yes
UK status
OTC licensed

Weight loss figures are from separate clinical trials and cannot be directly compared. Retatrutide is investigational and not approved by the MHRA as of June 2026. Consult a registered UK clinician before starting any weight management treatment.

"Clear improvements in assessed cardiometabolic health measures were recorded across all doses."

— Prof. Ania Jastreboff, Lead Investigator, Yale School of Medicine
Title

UK regulatory pathway: honest timeline

2023–2025

Phase 3 TRIUMPH trials initiated

8 trials across obesity, type 2 diabetes, osteoarthritis, cardiovascular risk.

May 2026

TRIUMPH-1 results published — pivotal obesity data

28.3% weight loss at 80 weeks. All doses met primary endpoints. Lilly expected to file FDA NDA Q3/Q4 2026.

Q3–Q4 2026

FDA submission — we are here

Priority review could shorten FDA timeline to 6 months → potential approval Q2–Q3 2027.

Late 2027 – mid 2028

MHRA marketing authorisation

Typically 4–12 months after FDA. Private prescriptions available within weeks of approval — before NHS access.

2029 onwards

NHS access via NICE technology appraisal

12–24 months post-MHRA. Phased rollout expected — highest BMI patients first. Scotland, Wales, NI assessed separately.
Title

Should I wait for retatrutide or start treatment now?

Start treatment now

Active weight-related comorbidities

Can't wait 18–24 months

Partial response to GLP-1s already

Consider: Mounjaro, Wegovy 7.2mg

Monitor PP405

Mild-moderate BMI, stable health

Plateau on Mounjaro / Wegovy

Willing to join a clinical trial

Register: NIHR Be Part of Research

Title

The scam problem: what's being sold online as "retatrutide"

Lab testing of UK-sold research peptides has found contamination, incorrect dosing, bacterial growth and in some cases entirely different substances in products sold as retatrutide. Products marketed as "retatrutide pens" at £120–£200 on Telegram and TikTok are not Eli Lilly's compound. The MHRA has already dismantled UK manufacturing operations producing fake GLP-1 pens...

Frequently asked questions

What is retatrutide and how does it differ from Mounjaro?

Retatrutide adds a third mechanism — glucagon receptor agonism — on top of the GLP-1 and GIP agonism that Mounjaro already uses. This increases energy expenditure, not just appetite suppression, which explains the higher weight loss figures in trials.

What did the TRIUMPH-1 Phase 3 results show?

All three doses met primary and key secondary endpoints. At 12mg, participants lost an average of 28.3% body weight at 80 weeks, with 45.3% achieving ≥30% loss — a threshold historically associated only with bariatric surgery.

When will retatrutide be available in the UK?

PP405 is being trialled in both men and women — unusually, it was designed for both sexes from the outset. This makes it potentially significant for women with female-pattern hair loss, who have very limited licensed options (finasteride is not MHRA-licensed for women).

What is the dysesthesia side effect and how common is it?

Dysesthesia is an abnormal tingling or painful skin sensation. It occurred in 20.9% of TRIUMPH-4 participants on the 12mg dose, vs 0.7% on placebo. Events were generally mild and rarely led to treatment discontinuation — but regulators will scrutinise this closely.

How much will retatrutide cost privately in the UK?

No official price announced. Based on Mounjaro pricing comparators and the more complex triple-action mechanism, analysts expect £200–£400/month at private launch — potentially higher if supply is constrained.

Are the retatrutide pens sold online real?

No. Independent lab testing of UK-sold peptide pens has found contamination, wrong concentrations, and in some cases entirely different substances. Retatrutide is not approved for sale anywhere in the world. Never buy from unregulated sources.

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