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 Week 5 vs Wegovy: What's the Difference?
By week 5 of treatment, you'll likely be settling into your Mounjaro or Wegovy routine—but which is right for you? Both are prescription-only GLP-1-type weight management injections licensed in the UK, but they work differently and progress through their dose schedules at different rates. At week 5, Mounjaro users are typically on a 5mg dose, while Wegovy users are escalating from 0.5mg. This comparison explains the key differences to help you understand how these medications compare, though only your prescriber can assess which is suitable for your individual circumstances.
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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 Differ at Week 5
Mechanism: Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—it activates two hormone pathways that regulate appetite and blood sugar. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. This dual action is why Mounjaro may produce different effects than Wegovy, though individual responses vary significantly.
Dose at week 5: Mounjaro follows a slower escalation—you'll typically be on 5mg at week 5 (after 4 weeks on the 2.5mg starting dose). Wegovy escalates more rapidly—at week 5 you're usually moving from 0.5mg towards 1mg. Despite different absolute doses, clinical trials showed Mounjaro produced average weight loss of around 15–21% body weight and Wegovy around 15% body weight, though results vary considerably between individuals.
What this means: The different dose schedules reflect different underlying pharmacology. Neither schedule is "better"—prescribers choose based on individual suitability following clinical assessment. Use our free GLP-1 weight loss calculator to explore projected weight loss outcomes with either medication.
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Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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Which Is Right for You?
Both Mounjaro and Wegovy require a UK prescription and clinical assessment—your GP or a licensed prescriber will decide based on your BMI, health conditions, and medical history. Neither is universally "better"; suitability is individual. Some people respond better to a dual mechanism (Mounjaro), others to a single mechanism (Wegovy). Some prefer weekly injections (both), others find the slower Mounjaro escalation easier to tolerate, whilst others prefer Wegovy's faster titration.
At week 5, side effects like nausea are often improving as your body adjusts, though this varies. Both medications require a reduced-calorie diet and increased physical activity to maximise results—injection alone is not sufficient. If you're unsure whether your current medication is working for you, discuss this with your prescriber; they can adjust your dose or explore alternatives based on your progress.
- 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.
What's the key difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist activating two hormone pathways, whilst Wegovy (semaglutide) is a GLP-1 agonist only. This dual mechanism may produce different effects, though clinical trial results for average weight loss were broadly similar—around 15–21% for Mounjaro and 15% for Wegovy. Individual results vary significantly.
What dose am I typically on at week 5 of Mounjaro vs Wegovy?
At week 5, Mounjaro users are usually on 5mg (after 4 weeks on the starting 2.5mg dose). Wegovy users are typically transitioning from 0.5mg towards 1mg. Mounjaro escalates more slowly; Wegovy escalates more rapidly. Both follow their own dose titration schedule designed for their respective pharmacology.
Which medication causes fewer side effects?
Both Mounjaro and Wegovy cause similar common side effects—nausea, diarrhoea, constipation, and stomach pain are very common. Individual tolerability varies; some people tolerate one better than the other. By week 5, many side effects improve as your body adapts, though this is not assured. Your prescriber can advise if tolerability becomes an issue.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official established conversion chart—your GP or prescriber will assess whether switching is appropriate and how to manage the transition safely. This typically requires a gap between doses and clinical guidance.
How do I know which medication is working better for me?
Progress is individual and varies week to week. Track your weight consistently using our free progress tracker and discuss results with your prescriber at regular reviews. At week 5, you may not yet see dramatic changes—most significant weight loss occurs over weeks 12–52 of treatment. Your prescriber can assess whether your current medication is right for you based on progress, tolerability, and your health goals.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.