Retatrutide vs Tirzepatide: Which Is Better? (October 2026)

01 · The verdict

Which is better for you: the verdict up front

If you are choosing a treatment in the UK now, tirzepatide is the only one of the two you can obtain through a regulated pathway. Mounjaro is the brand name for tirzepatide, a once-weekly injection licensed in the UK for weight management in adults and for type 2 diabetes.¹ Retatrutide has no UK licence.⁷ That single fact settles the practical question, whatever excitement surrounds the newer name.

Tirzepatide suits adults who meet the licensed weight-management criteria and want a medicine with large trial datasets, a published dose ladder and a prescriber who reviews them monthly. Retatrutide suits nobody as a purchase today: a vial from an unregulated seller has no regulated supply chain and no safety data behind that supply.⁷ If you are curious about future medicines, the sensible move is to start a licensed treatment now and ask your prescriber what changes if anything is licensed later.

Only SURMOUNT-5 supports a direct tirzepatide-versus-semaglutide comparison, and no trial compares tirzepatide with retatrutide.¹⁵

02 · Side by side

Tirzepatide vs retatrutide at a glance

03 · How to decide

The decision factors that actually matter

First, legality and accountability. A licensed medicine comes with a product leaflet, a manufacturer responsible for quality, a known storage and expiry regime and a prescriber who can report side effects through the Yellow Card scheme.¹⁹ An unlicensed peptide has none of those safeguards.

Second, evidence you can verify. Tirzepatide's results come from published trials, including the 2,539-adult SURMOUNT-1 trial and the 751-adult SURMOUNT-5 head-to-head.²¹⁵ Third, cost and continuity. You can see the full Mounjaro pen prices and consultation before you commit, and the consultation is free. Our guide to retatrutide versus tirzepatide cost goes further on money.

Fourth, your own health profile. Which licensed option is right depends on your medical history, tolerance and prescriber advice, not a headline number alone.¹⁵ To start, begin your free consultation; it is reviewed by a GPhC-registered prescriber, and unsuitable orders are refunded automatically.

04 · What each medicine is

What tirzepatide and retatrutide actually are

Tirzepatide is the active ingredient in Mounjaro, a once-weekly injectable prescription medicine made by Eli Lilly. In the UK it is licensed for weight management in adults and for type 2 diabetes. It comes as a pre-filled multi-dose pen, the KwikPen, in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ Prescription-only status means it is supplied only after a consultation reviewed by a GPhC-registered prescriber.

Retatrutide is a different matter. It has no UK licence, and the only way to buy it is as a so-called research peptide from sellers outside the regulated system.⁷ That is not a small technicality. A licence means a regulator has reviewed quality, safety and efficacy evidence, set a licensed dose and approved the product information. Without it, nobody has verified what is in a vial, how strong it is or how it was stored. The MHRA publishes counterfeit medicine alerts for precisely this reason.⁷

If a page tells you retatrutide is definitively "stronger", ask which trial, which dose, which duration and which population, and whether it has been compared head to head with tirzepatide in a peer-reviewed study.

How tirzepatide works is well described. It activates two natural gut-hormone receptors at once, GIP and GLP-1. Together these help regulate appetite, slow how quickly the stomach empties and improve how the body responds to insulin. Most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹ This dual action distinguishes it from single-action GLP-1 medicines such as semaglutide (Wegovy and Ozempic).

Tirzepatide's half-life is about five days, so after a final dose it takes roughly 4–5 weeks to clear the system. Nothing needs doing while it clears, and nothing speeds it up.¹ Remember too that treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them. For a wider look at the newer-medicine landscape, our comparison of retatrutide, semaglutide and tirzepatide sets out the same licensing picture for all three.

05 · Trial evidence

Weight loss results: what the trials say

Verified trial evidence for tirzepatide is detailed. In SURMOUNT-1, which enrolled 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks. The lifestyle-changes-alone group lost 3.1%.² These are trial averages, and individual results vary.

The distribution matters as much as the average. At 72 weeks, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of their body weight. Half of participants on 10mg and 57% on 15mg lost at least 20%.² As a worked example only, for someone starting at 100 kg, 20.9% is about 21 kg. Your own result depends on dose reached, diet, activity and biology, and trial averages do not predict your own result.

SURMOUNT-5 is the first large head-to-head trial in this class. In 751 adults over 72 weeks, average loss was 20.2% on tirzepatide versus 13.7% on semaglutide 2.4mg (Wegovy). Detailed results: at least 10% of body weight was lost by 81.6% on tirzepatide versus 60.5% on semaglutide; at least 15% by 64.6% versus 40.1%; at least 20% by 48.4% versus 27.3%; and at least 25% by 31.6% versus 16.1%. Average loss was 22.8 kg versus 15.0 kg.¹⁵ Both are effective, licensed treatments, and which suits you depends on health profile, tolerance and prescriber advice.

For context, in the STEP 1 trial adults on semaglutide 2.4mg lost on average 14.9% of body weight over 68 weeks, compared with 2.4% on placebo.⁹ Only SURMOUNT-5 supports a direct tirzepatide-versus-semaglutide comparison.

So where does that leave retatrutide? Honestly, in a gap. The question "which is stronger" therefore cannot be answered, and a confident answer from a seller or a social-media account should be treated with caution. Our retatrutide versus Mounjaro page covers the same ground from the brand angle.

06 · Dosage chart

Dosage chart: tirzepatide, Wegovy and retatrutide

A dosage chart is only meaningful for a licensed medicine, because a licence is what fixes the doses and schedule. Tirzepatide is injected once weekly and comes in six pen strengths. Each pen lasts four weeks, and your prescriber moves you up the ladder at a pace that suits your tolerance and response.¹

These are standard prices. A new customer's first order, at any dose, is £40 less with code FIRST40, and every later order is £25 less (code DOSE25). All six doses are in stock.

For comparison, Wegovy (semaglutide) pens are 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg once weekly. Titration steps up after at least four weeks and reaches the 2.4mg maintenance dose from week 17, which is the licensed maintenance dose for weight management.¹⁸ Milligram numbers are not comparable between the two medicines: 2.4mg of semaglutide is not equivalent to 2.4mg of anything else.

And retatrutide? There is no licensed dose, no titration schedule and no regulated product. Any chart you find online is not a prescribing standard. Vials from unregulated sellers carry no verified strength, which is exactly the situation the MHRA's counterfeit alerts address.⁷ Starting at an arbitrary dose of a product of unknown content is not something we, or any regulated prescriber, can support. Our page on retatrutide versus Mounjaro dosage explains the same point in more depth.

If you start Mounjaro and step up after 4 weeks on each dose, your first four pens (2.5mg to 10mg) cost £879.96 at standard prices before discounts. Not everyone needs to climb to the top strength; your prescriber reviews each step with you.

07 · Cagrilintide and others

Cagrilintide, mazdutide and other names you will see

Whether cagrilintide is better than tirzepatide is not something that can be answered with a figure. Figures vary, and your prescriber can advise.

First, check whether it holds a UK licence. A licensed weight-management medicine in the UK has been through regulator review and has a patient information leaflet and summary of product characteristics. The licensed injectable options we describe are Mounjaro (tirzepatide), Wegovy (semaglutide 2.4mg) and Saxenda (liraglutide), which is a daily injection supplied at 6mg per millilitre, unlike once-weekly Mounjaro and Wegovy.¹⁸

Two weight-loss tablets are now licensed in the UK as well: Wegovy tablets (oral semaglutide), approved by the MHRA in June 2026, and Foundayo (orforglipron), approved in August 2026. They are different medicines from Mounjaro, with their own dosing, eligibility checks and trial results, and both are prescription-only.²⁰²¹ For current Wegovy tablet pricing, see our weight loss treatments overview. There is no tablet form of Mounjaro: tirzepatide is injection-only in the UK.

Second, ask whether a named comparison is head to head. Only SURMOUNT-5 supports a direct tirzepatide-versus-semaglutide comparison. Lists ranking weight loss injections by setting different trials side by side are not comparing like with like, because populations, durations and designs differ.

Third, be wary of anything sold as a "research peptide". Mounjaro must not be combined with other GLP-1 medicines, unlicensed research peptides such as retatrutide, or compounded copies. These combinations have no safety data and no regulated supply chain.¹ If something promises faster results outside a licensed pathway, that is the warning sign.

If you are weighing several newer names against each other, our pages on mazdutide, tirzepatide and retatrutide and survodutide, tirzepatide and retatrutide apply the same evidence-first approach.

08 · Safety and side effects

Safety: what we know and what nobody can tell you

Safety is where the licensed-versus-unlicensed difference bites hardest. For tirzepatide, side effects are described in the product information, the patient leaflet and the prescribing references, and your prescriber reviews them with you.¹³ The commonest early effects are mild nausea, altered appetite and tiredness in the first days after each injection, and they usually settle.

For retatrutide, there is no licensed product information and no approved safety evidence. It is not a case of "no known problems": it is a case of no verified information at all about what you would actually be injecting. If you have kidney, heart or other conditions, discuss any weight-loss treatment with a prescriber who has your full history.

The additional risk with unregulated vials is contamination, mislabelling and counterfeit products. The MHRA publishes counterfeit medicine alerts and runs the Yellow Card scheme so that suspected side effects and fake products can be reported.⁷¹⁹ If you have already used an unlicensed peptide and feel unwell, get medical help straight away and report it. Do not stop being honest with your prescriber about what you have taken; they cannot manage a risk they do not know about.

For perspective on the licensed alternatives, side-effect data in STEP 1 showed gastrointestinal effects reported by 74.2% of people on semaglutide 2.4mg compared with 47.9% on placebo, and 7.0% stopped treatment because of side effects versus 3.1% on placebo.⁹ Our page on retatrutide versus Mounjaro side effects covers this further.

Stacking is the other big issue. People ask which peptide is best to stack with retatrutide. The straightforward answer is none: combinations of unlicensed products have no safety data and no regulated supply chain, and a plateau is not a reason to double doses or add unlicensed products.¹ If progress stalls, the licensed responses are to review food intake honestly, protect protein and activity, check sleep and alcohol, and discuss with your prescriber whether a dose step-up is appropriate if you are not yet at maximum.

Finally, new or worrying symptoms on any medicine deserve a conversation with the prescriber and, where relevant, a Yellow Card report.¹⁹

09 · PCOS and who it suits

PCOS, belly fat and who each option suits

Many readers arrive with a specific situation, and PCOS is a common one. Mounjaro is not licensed specifically for PCOS, but many women with PCOS meet the licensed weight-management criteria, and weight loss itself is a first-line recommendation that can improve insulin resistance, cycles and symptoms. Eligibility is assessed on the standard BMI criteria. Mention PCOS and any fertility plans in your consultation, because improving weight can restore ovulation, which matters for contraception and pregnancy planning. Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive; if you become pregnant during treatment, stop the medicine and tell your prescriber promptly. Mounjaro can reduce how well oral contraceptive pills are absorbed, so switch to a non-oral method, or add a barrier method such as condoms, for 4 weeks after starting and for 4 weeks after each dose increase.

The practical route for PCOS is the same as for anyone: a prescriber-reviewed consultation, a licensed treatment and a plan that includes diet and activity.

Belly fat is another frequent question: what shrinks belly fat fastest? What the tirzepatide trials show is average improvement in waist size, blood pressure, cholesterol and blood-sugar measures alongside weight loss, and most participants with prediabetes returned to normal blood-sugar levels. These are trial-average secondary outcomes, not promises, but they are why prescribers talk about weight management as health management rather than appearance.²

On pace, weight loss on Mounjaro is gradual by design. The first weeks on 2.5mg are an adjustment phase and losses are usually modest. Most measurable progress builds from 5mg onward, month by month, and trials measured results at 72 weeks. A sensible three-month expectation on a standard titration is mid single digits as a percentage of body weight, with wide individual variation, and slower early progress does not predict failure.² Treatment response is reviewed: if you have lost less than 5% of your starting weight after 6 months on the highest dose you can tolerate, your prescriber will discuss whether continuing or stopping is right for you.⁴

Who suits what, then? Tirzepatide suits adults who meet the licensed criteria, want a regulated supply and value verified evidence. Wegovy suits people for whom semaglutide is the better fit on health profile or tolerance, since both are effective licensed treatments. Neither injectable replaces a reduced-calorie diet and increased physical activity. Retatrutide, until and unless it is licensed, is not a treatment we or any regulated UK pharmacy can offer, and it is not appropriate to treat the unregulated market as a substitute for medical care.

10 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹

11 · Switching and ordering

Switching, stopping and how ordering works

Can you switch from retatrutide to tirzepatide? If you have already used an unlicensed peptide, tell the prescriber everything: product, dates and doses as best you know them. There is no licensed conversion between any of these medicines, and no approved guidance for coming off retatrutide specifically. For the licensed switch from semaglutide, the position is clear: there is no licensed direct conversion between semaglutide and tirzepatide. Switching is done under prescriber supervision, typically stopping the previous medicine, observing a washout interval and starting Mounjaro at a dose your prescriber judges appropriate, often the 2.5mg starting dose, sometimes adjusted based on your history.¹ Never run two GLP-1 medicines together, and do not combine Mounjaro with unlicensed research peptides.

If you are on tirzepatide and curious about something newer, the sensible approach is to stay on your licensed treatment and ask your prescriber at your monthly review. Because tirzepatide takes roughly 4–5 weeks to clear after a final dose, changes should be planned rather than improvised.¹

Ordering Mounjaro with us follows four steps. First, a free online consultation: a short health questionnaire with no charge and no obligation. Second, review by a GPhC-registered prescriber: payment is taken when you place the order, and if the prescriber decides the treatment is not suitable, the order is refunded automatically in full. Third, dispensing by our registered pharmacy, with same-day dispatch when ordered by 3pm. Fourth, free next-day tracked delivery in discreet, temperature-controlled packaging. Saturday delivery is £14.99.

We supply through official LillyDirect supply, meaning Mounjaro direct from Eli Lilly's UK distribution, genuine KwikPens, with all six doses stocked from 2.5mg to 15mg. You can check our registration on the GPhC register (9012878). Needles, a sharps bin and injection guidance are included with every order, and ongoing monthly reviews, dose titration and side-effect support are part of aftercare. Repeat orders re-check suitability, with no auto-shipping.

Support is available Monday to Friday, 9am to 5pm, by email at support@everydaymeds.co.uk, account portal chat or phone on 0333 207 0413. You can also track your journey with GLPTrackr, our free companion app for iOS and Android. If you are ready, see the Mounjaro pen page, or compare with the Wegovy pen.

Mounjaro (tirzepatide) is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber. It is used alongside a reduced-calorie diet and increased physical activity. Individual results vary. This page is information, not a substitute for medical advice.