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 6 vs Wegovy — What's the Difference?
By week 6 of treatment, you're likely on your first stable dose of either Mounjaro or Wegovy. Both are prescription-only GLP-1-based weight management injections licensed in the UK, but they work slightly differently and show different results in clinical trials. This guide compares the two medications to help you understand which might be more suitable for your situation, and how they differ in terms of mechanism, dosing schedule, and expected outcomes. Your prescriber will assess your individual health needs to recommend the right choice for you.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
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.
Clinical Trial Data and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. This dual action may contribute to greater appetite suppression and food craving reduction. In the SURMOUNT-1 clinical trial, participants on 5 mg (typically reached by week 6) achieved an average weight loss of approximately 15% of body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, targeting a single hormone pathway. In the STEP-1 trial, participants achieved an average weight loss of approximately 14.9% of body weight at the maximum 2.4 mg dose over 68 weeks. By week 6, most patients are still in the escalation phase and have not yet reached the maintenance dose.
- Mounjaro: dual GIP + GLP-1 mechanism; once-weekly injection; reaches 5 mg by week 4–5
- Wegovy: GLP-1 only; once-weekly injection; typically still escalating at week 6 (usually on 0.5 mg or 1 mg)
- Both show meaningful weight loss in clinical trials; individual results vary significantly
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How It Works
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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Dosing, Side Effects, and Individual Suitability
At week 6, you're likely on 5 mg of Mounjaro (after reaching this dose by week 4) or still escalating Wegovy through 0.5 mg or 1 mg doses. Both medications can cause nausea, diarrhoea, and constipation — especially during the dose escalation phase. These side effects often settle as your body adjusts.
The choice between Mounjaro and Wegovy depends on your individual health profile, tolerability, and GP or prescriber assessment. Neither medication is "better" — both are effective for suitable candidates. Your prescriber will consider your medical history, any other medications, and whether the dual mechanism of Mounjaro suits you better than the single GLP-1 mechanism of Wegovy. Use our GLP-1 weight loss calculator to estimate potential outcomes with either medication, and track your progress with our free progress tracker as you continue your treatment.
- 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 main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist (two hormone pathways), while Wegovy is a GLP-1 receptor agonist only (one pathway). This dual mechanism may make Mounjaro slightly more effective for appetite suppression, though both medications support meaningful weight loss when combined with lifestyle changes.
What dose of Mounjaro or Wegovy will I be on at week 6?
By week 6, you're typically on 5 mg of Mounjaro (reached by week 4). With Wegovy, you're usually still in the escalation phase, around 0.5 mg or 1 mg. Wegovy takes 17 weeks to reach the maximum 2.4 mg dose, whereas Mounjaro reaches 15 mg over approximately 20 weeks.
Which one causes fewer side effects?
Both medications cause similar common side effects: nausea, diarrhoea, and constipation — especially during dose escalation. Individual tolerance varies. Side effects often settle after a few weeks as your body adjusts. Your prescriber can advise on managing them.
How much weight loss should I expect by week 6?
By week 6, you're typically still in the early phase of treatment. Meaningful weight loss usually becomes noticeable between weeks 8 and 16. Trial data shows average weight loss of 15–21% over 68–72 weeks, but results vary individually. Your progress tracker can help you monitor your journey.
Which medication should I choose?
This is a decision for your prescriber based on your medical history, other medications, and individual health factors. Both are prescription-only, require a clinical assessment, and must be combined with dietary and lifestyle changes. Your GP or specialist will recommend the most suitable option for you.
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.