The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro 5mg vs Wegovy — What's the Difference?
If you're considering prescription weight loss treatment in the UK, you may have heard of both Mounjaro and Wegovy. Both are weekly weight loss injections licensed for adults with obesity or overweight with health conditions, but they work in different ways and have different dose ranges. Understanding how they compare helps you and your prescriber decide which might be right for you. This guide breaks down the key differences between Mounjaro's 5mg dose and Wegovy, based on clinical evidence and NHS guidance.
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What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How Mounjaro and Wegovy Work Differently
The fundamental difference between these two weekly weight loss injections lies in their mechanism of action. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in the body. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) work together to regulate appetite, reduce cravings, and help you feel fuller after smaller meals.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating just the GLP-1 pathway. This single mechanism still helps with appetite suppression and satiety, but does not activate the GIP pathway.
In clinical trials, this dual-action approach of Mounjaro has shown slightly higher average weight loss compared to Wegovy. At the 5mg dose, Mounjaro showed approximately 15% average body weight loss in the SURMOUNT-1 trial, whilst Wegovy showed approximately 14.9% average weight loss in the STEP-1 trial — though individual results vary significantly. Both medications are prescription-only and require a clinical assessment before being prescribed.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Dose Ranges and Clinical Context
Mounjaro's 5mg dose is a maintenance dose typically reached after four weeks of dose titration starting from 2.5mg. Mounjaro's dose range spans from 2.5mg up to 15mg weekly. Wegovy, by contrast, starts at 0.25mg and escalates to a maximum of 2.4mg weekly. This means Mounjaro's therapeutic doses are considerably higher in absolute terms.
Both are given as a once-weekly injection via a KwikPen or pre-filled pen. The choice between them depends on individual health factors, how your body responds during dose titration, and your prescriber's clinical assessment. Your GP can refer you to an NHS specialist weight management service, or you can access these medications through private prescribing following an online clinical consultation. Our free GLP-1 weight loss calculator can help you understand potential outcomes with different doses, and use our BMI calculator to track where you stand on NHS health guidelines.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is Mounjaro 5mg stronger than Wegovy?
Mounjaro's 5mg dose is not directly comparable to Wegovy's doses because they use different mechanisms and dose ranges. Mounjaro activates both GIP and GLP-1 pathways, whilst Wegovy activates GLP-1 only. Clinical trial data suggests Mounjaro may produce slightly higher average weight loss, but individual results vary significantly. Your prescriber will assess which is more suitable for you.
Can I switch from Wegovy to Mounjaro 5mg?
Switching between these medications is possible but must be managed by your prescriber. There is no official conversion chart, but approximate clinical equivalence suggests Wegovy 1.7mg is similar to Mounjaro 5mg. Any switch requires a new assessment and prescription. Do not change medications without medical guidance.
What are the side effects of Mounjaro 5mg compared to Wegovy?
Both medications cause similar common side effects: nausea, diarrhoea, vomiting, constipation, and stomach pain — particularly during dose escalation. Mounjaro users report comparable side effect profiles to Wegovy users in clinical trials. Most side effects are temporary and improve as your body adjusts. Always report persistent or concerning symptoms to your prescriber.
How do I access Mounjaro or Wegovy on the NHS in the UK?
Both medications are available through NHS specialist tier 3 weight management services. You'll need a GP referral and assessment. Access varies significantly by region and availability can involve waiting lists. Private access is available through GPhC-registered online pharmacies following a clinical assessment, without needing an NHS referral.
Which weight loss injection should I choose — Mounjaro or Wegovy?
This is a decision for you and your prescriber based on your individual health, medical history, previous medication responses, and clinical assessment. Both are prescription-only and require clinical evaluation. Factors like your BMI, comorbidities, and how you respond to GLP-1 medications will influence suitability. Your GP or prescriber will advise which is appropriate for you.
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