Wegovy vs Mounjaro vs Retatrutide: What UK Adults Should Know Right Now

Step 1 — Understand what each medicine actually does (the mechanisms are not interchangeable)

Wegovy is semaglutide, a GLP-1 receptor agonist made by Novo Nordisk. It mimics a gut hormone that reduces appetite, slows gastric emptying and helps regulate blood sugar. Mounjaro is tirzepatide, made by Eli Lilly. It activates both GIP and GLP-1 receptors, the only dual-agonist weight-loss medicine licensed in the UK. Adding a second pathway appears to produce a meaningful additional effect on fat tissue and appetite signalling, and the trial evidence broadly reflects that.

Retatrutide goes further still: it is a triple agonist, targeting GIP, GLP-1 and glucagon receptors simultaneously. Early phase 2 trial data, published in the New England Journal of Medicine, reported average weight losses well above those seen with either licensed medicine. That is genuinely interesting. It is also the point where many readers assume retatrutide is available, a common misconception worth gently correcting. As of summer 2026 it remains an investigational compound. No phase 3 trial results have been published, no regulatory submission has been made to the MHRA, and there is no licensed product to prescribe in the UK or anywhere else. Sellers offering retatrutide online are selling something outside any approved supply chain.

Understanding the mechanism matters because it shapes the eligibility conversation. The differences between semaglutide, tirzepatide and retatrutide go beyond marketing names, and a prescriber will factor in your health history when weighing up which receptor targets are appropriate for you.

Step 2, Look at what the licensed trial data actually shows

The table below summarises the headline evidence for the two medicines you can currently access, alongside what is known about retatrutide.

In the SURMOUNT-5 open-label trial) 751 adults with obesity, no diabetes, over 72 weeks, tirzepatide produced a greater average weight reduction than semaglutide 2.4mg head-to-head. NICE's appraisal of tirzepatide (TA1026) noted that indirect comparisons also favour tirzepatide, while acknowledging the limitations of cross-trial analysis. The 7.2mg Wegovy pen, approved by the MHRA in April 2026, narrows that gap considerably. Which of these figures is relevant to you depends on your clinical profile, not on which sounds most impressive in a comparison table.

Step 3, Check who is eligible for the two licensed options

Both Mounjaro and Wegovy share broadly similar private eligibility criteria: adults with a BMI of 30 or above, or 27 or above alongside a weight-related condition such as high blood pressure, type 2 diabetes, high cholesterol or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. A prescriber assesses the full picture, not just the number on the scale. The head-to-head comparison of Wegovy and Mounjaro covers eligibility nuances in more depth, including the NHS phases.

On the NHS, tirzepatide was recommended by NICE in December 2024 (TA1026) for adults with a BMI of 35 or above alongside at least one weight-related comorbidity, accessed through a phased rollout. Wegovy was recommended under TA875, maximum two years, within a specialist weight management service. Neither route is quick. Private prescription through a GPhC-registered pharmacy is the realistic option for most people who do not meet current NHS criteria or do not want to wait. You can verify any online pharmacy on the GPhC register.

Retatrutide has no eligibility criteria in the UK because there is nothing to prescribe. If you are still weighing up whether Wegovy or Mounjaro is the better fit for your situation, that is the genuinely useful question to pursue right now. Anyone wondering about cost can set that question aside for now; the Mounjaro and Wegovy price comparison covers what licensed treatment actually costs in the UK.

Step 4, What this means when you speak to a prescriber

The practical upshot is straightforward. If you are researching this three-way comparison, your realistic decision today is between Mounjaro and Wegovy. Both are clinically proven, both are licensed, both carry a Black Triangle designation indicating ongoing MHRA monitoring. Common side effects across both run to a familiar GI pattern (nausea, loose stools, constipation, reflux) typically most pronounced in the first weeks or after a dose step. The NHS tirzepatide page and the equivalent semaglutide page set this out clearly for patients.

Retatrutide may eventually complete phase 3 trials, receive regulatory review and reach a licensed market. That process takes years and is outside anyone's control. Buying anything labelled retatrutide today would mean purchasing an unlicensed compound with no approved manufacturing standards, no MHRA oversight and no clinical evidence from a population representative of UK adults. That is a meaningful risk, not a technicality. The MHRA's warnings about fake and unlicensed weight-loss medicines are worth reading if you have seen retatrutide offered online.

Which of the two licensed medicines is the right fit involves your medical history, any medicines you already take, and how you feel about injections versus an oral option. That is a clinical decision our prescribers make with you. Speak to our prescribers by starting your free consultation; it is reviewed the same day by a real clinician. If you want to read more broadly first, our detailed breakdown of tirzepatide versus Wegovy sets out the full landscape, and this comparison of semaglutide and Mounjaro goes further on the mechanism differences.