What's the Difference Between Tirzepatide and Retatrutide? (October 2026)

01 · The short verdict

Tirzepatide vs retatrutide: the verdict

For anyone in the UK who wants a weight-loss injection, tirzepatide is the only one of the two that can be prescribed, dispensed and supported by a regulated pharmacy. It is licensed for weight management in adults and for type 2 diabetes, and it comes as a once-weekly KwikPen in six strengths from 2.5mg to 15mg.¹ Retatrutide has no UK licence, so there is no UK product information to check, no approved dose and no regulated supplier.¹

Tirzepatide suits you if: you are an adult wanting medically supervised weight management, you want a prescriber-reviewed plan, and you want genuine, traceable pens with follow-up support.

Retatrutide does not suit anyone as a UK purchase today: products sold as retatrutide online sit outside the licensed pathway. If something promises faster results outside a licensed pathway, that is the warning sign.¹

02 · Side by side

Tirzepatide and retatrutide compared

03 · How to decide

The decision factors that matter

The first factor is legality and traceability. A licensed pen from a GPhC-registered pharmacy has a known manufacturer, a patient information leaflet and a prescriber who can adjust your dose. An unlicensed vial has none of these.

The second is evidence you can read. Tirzepatide's results are published in the New England Journal of Medicine, with named trials and stated durations.²

The third is follow-up. Our prescribing team provides monthly reviews, dose titration and side-effect support, and repeat orders re-check suitability. Starting is straightforward: start your free consultation, and if you are unsuitable, the order is refunded automatically.

If you want to compare tirzepatide with other licensed options instead, our guide to the semaglutide and tirzepatide differences uses head-to-head trial data, and the full list of weight loss treatments shows what else is available.

04 · What tirzepatide is

What tirzepatide is and how it works

Tirzepatide is the active ingredient in Mounjaro, a once-weekly injectable prescription medicine made by Eli Lilly.¹ 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

It is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1. Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin.¹ In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹

It is a dual action, which distinguishes it from single-action GLP-1 medicines such as semaglutide (Wegovy and Ozempic).¹ Tirzepatide has a half-life of about five days, so after a final dose it takes roughly 4–5 weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹

05 · Retatrutide's UK status

Where retatrutide stands in the UK

Retatrutide has no UK licence.¹

You will see it advertised online as a "research" peptide. Those products have no safety data for use in people and no regulated supply chain.¹ The MHRA publishes counterfeit medicine alerts for good reason.⁷

Our related guides cover the Mounjaro and retatrutide comparison and the differences between reta and tirzepatide.

06 · Tirzepatide trial evidence

What the trial evidence shows for tirzepatide

In the SURMOUNT-1 trial of 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, compared with 3.1% with lifestyle changes alone.² These are trial averages. Individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.²

As a worked example, for someone starting at 100 kg, 20.9% is about 21 kg. Trial averages do not predict your own result.

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% of their body weight.²

SURMOUNT-5 is the first large head-to-head trial of tirzepatide and semaglutide for weight loss. In that first large head-to-head trial, adults on tirzepatide lost on average 20.2% of body weight over 72 weeks versus 13.7% on semaglutide 2.4mg (Wegovy).¹⁵ Both are effective, licensed treatments. Which suits you depends on your health profile, tolerance and prescriber advice, not the headline number alone.¹⁵ In the separate 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 Those two trials should not be set side by side, because only SURMOUNT-5 compared the medicines directly. For more detail, see our guide to the differences between semaglutide and tirzepatide and the Mounjaro and Wegovy comparison.

07 · Safety and stacking

Safety: why you should not combine them

Mounjaro must not be combined with other GLP-1 medicines, unlicensed "research" peptides (such as retatrutide, which has no UK licence), or compounded copies.¹ These combinations have no safety data and no regulated supply chain.¹ People sometimes ask whether they can "stack" a licensed pen with a research peptide to get more. The answer is no: these combinations have no safety data.

If you take a licensed medicine, follow the patient information leaflet and your prescriber's instructions. If you notice a new or lasting symptom, tell your prescriber, and you can report suspected side effects through the MHRA Yellow Card scheme.¹⁹ 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 or eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing.

Two practical warning signs of an unsafe seller are an offer to supply without a consultation or prescription, and dramatic weight-loss claims that go beyond published trial averages. A regulated pharmacy will always ask about your health first. You can check any UK pharmacy on the GPhC register; ours is registration 9012878.¹²

The wider confusion around peptides is covered in our explainer on the difference between tirzepatide and peptides.

08 · Getting tirzepatide in the UK

How to get tirzepatide in the UK

There are two routes: the NHS and regulated private treatment. Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first (initially BMI 40+ with four or more qualifying conditions).⁴⁶ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.

Privately, the process with us has four steps:

• A free online consultation: a short health questionnaire, no charge and no obligation.
• A review by a GPhC-registered prescriber. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full.
• Dispensing by our registered pharmacy, with same-day dispatch when ordered by 3pm.
• Free next-day tracked delivery in temperature-controlled packaging. Saturday delivery is £14.99.

All six doses are in stock, supplied through official LillyDirect supply. Standard prices per month (one 4-week pen) run from £169.99 at 2.5mg to £299.99 at 15mg, as of October 2026. New customers save £40 on their first order with code FIRST40, and an automatic £25 reorder discount applies to every future order (code DOSE25). If you step up after 4 weeks on each dose, your first four pens (2.5mg to 10mg) cost £879.96 at standard prices. You can view the Mounjaro pen prices and consultation at any time.

09 · Other comparisons

Saxenda, semaglutide and which injection is best

No licensed medicine is best for everyone; your prescriber decides what suits you. An unlicensed product described as "stronger" has no UK product information.

Saxenda (liraglutide) is a different type of product. Liraglutide is supplied at a concentration of 6mg per millilitre and is a daily injection, unlike once-weekly Mounjaro and Wegovy.

Wegovy (semaglutide) is a once-weekly injection whose dose ladder runs 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg, stepping up after at least four weeks and reaching the 2.4mg maintenance dose from week 17.¹⁸ Tirzepatide's difference is that it acts on two receptors rather than one.¹

The phrase "poor man's Ozempic" is a nickname for low-cost supplements marketed as alternatives. These are available cheaply without assessment, with no clinical oversight, and their dosing is not standardised. They are not equivalent to a licensed medicine, and no trial result for tirzepatide or semaglutide applies to them.

There is also a page on retatrutide and tirzepatide differences.