UK weight loss injection comparison
Mounjaro vs Wegovy: Which Weight Loss Injection Is Better?
Mounjaro and Wegovy are two of the leading prescription weight loss injections available in the UK. Both can help eligible patients lose weight, reduce appetite and improve weight-related health risks, but they work in different ways and may suit different people.
This guide compares Mounjaro and Wegovy using current clinical evidence, including the latest head-to-head trial data, UK guidance and practical considerations such as side effects, dosing, switching and long-term maintenance.
Quick Answer: Is Mounjaro Better Than Wegovy?
For average weight loss, current evidence generally favours Mounjaro. Mounjaro contains tirzepatide, which acts on both GIP and GLP-1 receptors. Wegovy contains semaglutide, which acts on GLP-1 receptors.
In the SURMOUNT-5 head-to-head clinical trial, tirzepatide produced greater average weight loss and waist circumference reduction than semaglutide over 72 weeks. However, this does not mean Mounjaro is automatically the best option for every patient. Wegovy remains an effective treatment and may be more suitable for some people depending on medical history, previous treatment response, side effects, cardiovascular risk, availability and prescriber assessment.
Bottom line: Mounjaro currently has stronger evidence for greater average weight loss, but the right treatment should always be chosen after a clinical review.
Mounjaro vs Wegovy: At a Glance
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Active ingredient | Tirzepatide | Semaglutide |
| Medicine type | Dual GIP and GLP-1 receptor agonist | GLP-1 receptor agonist |
| Injection frequency | Once weekly | Once weekly |
| UK weight management licence | Yes | Yes |
| Average weight loss | Generally higher in current head-to-head evidence | Strong evidence, with newer higher-dose semaglutide data emerging |
| Common side effects | Nausea, diarrhoea, constipation, vomiting, reduced appetite | Nausea, diarrhoea, constipation, vomiting, fatigue |
| May suit | Patients seeking larger average weight loss, where clinically suitable | Patients who tolerate semaglutide well or where Wegovy is clinically preferred |
How Do Mounjaro and Wegovy Work?
How Wegovy Works
Wegovy contains semaglutide. It works by mimicking GLP-1, a naturally occurring hormone involved in appetite regulation, fullness, digestion and blood sugar control. By activating GLP-1 receptors, Wegovy can reduce hunger, help patients feel fuller for longer and support weight loss alongside lifestyle changes.
How Mounjaro Works
Mounjaro contains tirzepatide. It activates both GIP and GLP-1 receptors. This dual incretin action is thought to improve appetite control, satiety and metabolic response, which helps explain why Mounjaro has shown greater average weight loss in clinical studies.
Clinical Evidence: What Do the Latest Trials Show?
The evidence base for both treatments is strong, but recent head-to-head data has made the comparison clearer. Mounjaro has shown greater average weight loss than standard-dose Wegovy in a direct comparison, while Wegovy remains a well-established treatment with important evidence for weight loss and cardiovascular risk reduction in selected patients.
| Study or guidance | Treatment | What it showed | Why it matters |
|---|---|---|---|
| SURMOUNT-1 | Tirzepatide | Substantial and sustained body weight reduction over 72 weeks | Supports Mounjaro’s effectiveness for weight management |
| SURMOUNT-5 | Tirzepatide vs semaglutide | Tirzepatide was superior to semaglutide for weight and waist reduction at 72 weeks | The most important direct comparison between Mounjaro and Wegovy |
| STEP trials | Semaglutide | Clinically meaningful weight loss with semaglutide 2.4mg | Supports Wegovy as an effective weight loss treatment |
| Wegovy 7.2mg approval | Higher-dose semaglutide | The MHRA has approved a higher 7.2mg dose for adult patients with obesity | Newer Wegovy evidence may narrow the gap for some patients |
| NICE guidance | Mounjaro and Wegovy | Both medicines have important UK guidance depending on indication and patient group | Treatment should be clinically appropriate and evidence-led |
References include published clinical trial evidence and UK regulatory/guidance sources such as NEJM, MHRA and NICE. This page is for general information only and does not replace individual medical advice.
Weight Loss Results: Mounjaro vs Wegovy
In general, Mounjaro has produced greater average weight loss than standard-dose Wegovy in clinical evidence. This is one reason many patients ask whether they should start Mounjaro or switch from Wegovy to Mounjaro.
However, real-world results vary. Your outcome can depend on starting weight, dose, side effects, diet, activity levels, sleep, alcohol intake, medical conditions, other medicines and how consistently treatment is used.
Practical interpretation
If your main priority is the highest average weight loss, Mounjaro may be the stronger option. If you have tolerated Wegovy well, have specific cardiovascular considerations, or have already had good results with semaglutide, Wegovy may still be appropriate.
Side Effects: Is Mounjaro or Wegovy Easier to Tolerate?
Both Mounjaro and Wegovy can cause side effects, especially during the first few weeks of treatment or after dose increases. Most common side effects are gastrointestinal.
| Side effect | Mounjaro | Wegovy |
|---|---|---|
| Nausea | Common | Common |
| Constipation | Common | Common |
| Diarrhoea | Common | Common |
| Vomiting | Can occur | Can occur |
| Reduced appetite | Common and expected | Common and expected |
| Fatigue | Can occur | Can occur |
Side effects are often mild to moderate and may improve as your body adjusts. Some patients need slower dose increases, additional dietary advice or a treatment review. You should seek urgent medical advice if you develop severe abdominal pain, persistent vomiting, signs of dehydration, symptoms of gallbladder problems, symptoms of pancreatitis, allergic reaction symptoms or any concerning new symptoms.
Dosing: How Do the Treatment Schedules Compare?
Both treatments are taken once weekly and are usually increased gradually to reduce side effects and improve tolerability.
| Treatment | Typical starting dose | Dose escalation | Maintenance doses |
|---|---|---|---|
| Mounjaro | 2.5mg once weekly | Usually increased every 4 weeks if suitable | 5mg, 7.5mg, 10mg, 12.5mg or 15mg depending on response and tolerance |
| Wegovy | 0.25mg once weekly | Usually increased gradually if suitable | Commonly 2.4mg, with higher-dose 7.2mg now approved for adult patients with obesity |
Dose increases are not automatic. A prescriber may advise staying on the same dose for longer if appetite control is good or side effects are troublesome.
Eligibility for Mounjaro or Wegovy in the UK
Private weight loss treatment is usually considered for adults with a BMI of 30 or above, or a BMI of 27 or above with a weight-related health condition. Suitability is always assessed individually.
These medicines may not be suitable during pregnancy or breastfeeding, or for people with certain medical conditions, eating disorder history, pancreatitis history, gallbladder disease, significant gastrointestinal disease, or specific medication risks. A clinician will review your medical questionnaire, BMI, health history and current medication before deciding whether treatment is appropriate.
Can You Switch From Wegovy to Mounjaro?
Some patients can switch from Wegovy to Mounjaro, but it should only be done after a clinical review. The prescriber will consider your current dose, side effects, weight loss response, BMI, medical history, treatment gap and whether it is safer to restart at a lower dose.
You should not overlap Wegovy and Mounjaro or change between treatments without professional guidance. If you have had a treatment break, you may need to restart at a lower dose to reduce the risk of side effects.
For more information, read our guidance on switching weight loss injections or contact our pharmacy team for advice.
Mounjaro vs Wegovy Prices
Price is important, but it should not be the only factor. Patients should compare the full service, including clinical assessment, pharmacy support, delivery, follow-up, safety checks and whether the provider is appropriately registered.
You can compare our current treatment information and pricing here:
Lifestyle Support: Getting the Best Results
Mounjaro and Wegovy can reduce appetite, but long-term results are stronger when treatment is paired with sustainable lifestyle changes. This does not mean extreme dieting. It means building habits that are realistic enough to continue.
Protein
Prioritise lean protein such as chicken, fish, eggs, Greek yoghurt, tofu, lentils and beans.
Fibre
Include vegetables, fruit, wholegrains and legumes to support fullness and digestion.
Hydration
Drink regularly, especially if appetite is reduced or you experience nausea or constipation.
Movement
Walking, resistance training and light activity can help protect muscle and support weight maintenance.
Read more in our Mounjaro lifestyle tips guide.
Which Treatment Should You Choose?
| Your priority | Treatment that may be considered | Why |
|---|---|---|
| Highest average weight loss | Mounjaro | Head-to-head evidence favours tirzepatide over standard-dose semaglutide. |
| Established GLP-1 treatment | Wegovy | Wegovy has strong clinical evidence and may suit some patients well. |
| Previous poor response to Wegovy | Mounjaro may be reviewed | A switch may be appropriate after clinical assessment. |
| Previous good response to Wegovy | Wegovy may remain suitable | There may be no need to switch if it is effective and well tolerated. |
| Complex medical history | Requires prescriber decision | Safety and suitability matter more than headline weight loss results. |
FAQs
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