Description
How it works
GLP-1 medicines like Wegovy work on a single hormone receptor. Mounjaro adds a second (GIP). Retatrutide adds a third — glucagon — into the mix. Each pathway contributes a different effect:
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GLP-1 reduces appetite, slows stomach emptying, and helps regulate blood sugar (the same pathway as Wegovy).
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GIP improves how the body handles fats and amplifies the appetite-suppressing effect of GLP-1 (the same pathway added by Mounjaro).
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Glucagon activation, at the right level, increases the body's resting energy expenditure — meaning the body burns slightly more energy at rest, even before factoring in reduced food intake.
The combination is designed to deliver greater weight loss than either single- or dual-receptor approaches by addressing both sides of the energy balance equation: less in (appetite), and more out (energy expenditure).
Who it may be suitable for
Retatrutide isn't licensed yet, so no eligibility criteria are formally set. Based on Lilly's Phase 3 programme and existing UK GLP-1 prescribing patterns, it is being studied in:
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Adults with a BMI of 30 or above (obesity)
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Adults with a BMI of 27 or above who also have at least one weight-related health condition (such as type 2 diabetes, high blood pressure, high cholesterol, obstructive sleep apnoea, or knee osteoarthritis)
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Adults with type 2 diabetes, with or without obesity (in the TRANSCEND-T2D programme)
Retatrutide is being studied as part of a structured plan that also includes a reduced-calorie diet and increased physical activity — not as a standalone treatment.
Side Effects
The most common side effects in retatrutide trials have been gastrointestinal, in line with the wider GLP-1 class, and most noticeable during dose increases:
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Nausea, indigestion or reflux
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Vomiting
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Diarrhoea or constipation
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Reduced appetite (also the intended effect)
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Headache, dizziness or fatigue in the early weeks
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Injection-site reactions (mild, usually short-lived)
A side effect to be aware of: dysesthesia
In the TRIUMPH-4 Phase 3 trial, around 21% of participants on the highest 12 mg dose reported dysesthesia — an unusual skin sensation often described as tingling, sensitivity to touch, or mild burning. Most cases were mild, and discontinuation rates remained low, but this is a side effect that hasn't been prominent with semaglutide or tirzepatide and is worth being aware of as a potentially distinguishing feature of retatrutide.
Typical GLP-1 comfort tips
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Eat smaller, slower meals and stop at comfortable fullness
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Prioritise lean protein, fibre and fluids; keep very fatty or spicy foods modest
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Avoid lying flat immediately after eating if you're prone to reflux
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Gentle walks can help with bloating
Additional Info
As a GLP-1-class medicine, retatrutide is likely to share the class-level cautions seen across this group of treatments: a class warning regarding thyroid C-cell tumours based on animal studies (not confirmed in humans), avoidance in people with a personal or family history of medullary thyroid cancer or Multiple Endocrine Neoplasia syndrome type 2, and known class risks of pancreatitis and gallbladder problems. Because retatrutide also activates the glucagon receptor — a novel addition for this drug class — its long-term cardiovascular and metabolic safety profile is still being characterised. Definitive UK-specific precautions will only be confirmed once the MHRA reviews and licenses the medicine.
FAQs
Is retatrutide available on the NHS?
No. Retatrutide is not licensed anywhere in the world, so it cannot be prescribed on the NHS or privately in the UK. Even after any future MHRA approval, NHS availability would depend on a separate appraisal by the National Institute for Health and Care Excellence (NICE), which usually adds several months. Realistic NHS access is unlikely before 2028 or 2029.
When will retatrutide be available in the UK?
No timeline has been confirmed. Eli Lilly has not yet submitted a marketing application to any regulator. Industry expectation is for an FDA filing in late 2026 or early 2027, with a US decision potentially in late 2027 or 2028. UK MHRA approval would typically follow the FDA's lead by 6–12 months. A realistic earliest window for private UK prescribing is 2028.
Can I buy retatrutide online now?
No. Retatrutide isn't licensed in any country, so there is no legitimate supply through a UK pharmacy. Any website, social media account or "research peptide" supplier offering retatrutide for human use is doing so unlawfully, and cannot guarantee that the product is genuine, sterile, correctly dosed or safe. This is one of the riskier corners of the unlicensed weight-loss-drug market — please don't.
How does retatrutide compare to Wegovy and Mounjaro?
On weight loss alone, the published trial figures put retatrutide ahead of both. Wegovy's pivotal STEP-1 trial showed about 15% average weight loss; Mounjaro's SURMOUNT-1 trial showed about 21% at the 15 mg dose; retatrutide's TRIUMPH-4 trial showed about 29% at the 12 mg dose. However, Wegovy and Mounjaro are approved, established treatments with long real-world safety records, while retatrutide is still being studied. The dysesthesia (skin sensitivity) finding is also unique to retatrutide and not seen at the same rate with semaglutide or tirzepatide.
Why does it have three "agonist" actions instead of one?
Wegovy works through one hormone pathway (GLP-1). Mounjaro works through two (GLP-1 and GIP). Retatrutide adds a third — glucagon — which contributes to weight loss by raising the body's energy expenditure, in addition to suppressing appetite. The hypothesis behind the triple-agonist approach is that combining three complementary mechanisms produces greater weight loss than any single or dual approach.
What is dysesthesia, and should I be worried about it?
Dysesthesia is an unusual skin sensation — typically tingling, mild burning, or sensitivity to touch. In the TRIUMPH-4 trial, it was reported by around 21% of participants at the highest 12 mg dose of retatrutide. Most cases were mild and didn't lead to people stopping treatment, but it's a side effect that hasn't been prominent with semaglutide or tirzepatide. As more Phase 3 data is published, the picture should become clearer.
Can I put my name on a waiting list?
We don't keep waiting lists for unlicensed medicines. The most reliable way to stay updated is to subscribe to our newsletter — we publish updates as UK licensing develops. If you'd like to start a weight management treatment now, our weight loss service offers consultations for Wegovy and Mounjaro.
What happens if I stop taking retatrutide?
Evidence across the GLP-1 class consistently shows that stopping treatment leads to some weight regain over time, particularly without sustained changes to diet and activity. Whether retatrutide's longer-term picture differs from Wegovy or Mounjaro will only become clear once long-term Phase 3 data is published.
Who makes retatrutide?
Retatrutide (development code LY3437943) is being developed by Eli Lilly and Company, the same pharmaceutical company behind Mounjaro and the recently FDA-approved oral GLP-1 tablet, Foundayo (orforglipron).
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