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 and Wegovy Doses Explained
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available in the UK, but they work differently and use different dose ranges. Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg once weekly, whilst Wegovy begins at 0.25 mg and reaches 2.4 mg maximum. Understanding how these doses compare, what they achieve in clinical trials, and how they're prescribed can help you discuss options with your GP or a licensed prescriber. Both require clinical assessment and work best alongside lifestyle changes.
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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.
Mounjaro vs Wegovy: Dose Ranges and Mechanism
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two separate hormone pathways to regulate appetite and blood sugar. Starting at 2.5 mg, the dose increases every 4 weeks through 5 mg, 7.5 mg, 10 mg, 12.5 mg, to a maximum of 15 mg once weekly. Each KwikPen contains four doses (four weeks' supply).
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway. It starts at 0.25 mg and escalates over five weeks through 0.5 mg, 1 mg, and 1.7 mg, reaching 2.4 mg maximum once weekly. The lower starting dose and slower escalation mean it takes longer to reach maintenance.
The key difference: Mounjaro's dual mechanism may offer stronger appetite suppression, whilst Wegovy's single mechanism has a longer safety history (semaglutide has been used for diabetes management since 2017). Clinical trial data from SURMOUNT (Mounjaro) and STEP (Wegovy) both show significant weight loss, though results vary between individuals. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
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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.
Free Weight Loss Tools & Guides
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Clinical Trial Results and Individual Suitability
In the SURMOUNT-1 trial, participants on Mounjaro 15 mg lost an average of 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy 2.4 mg achieved approximately clinically studied weight loss over 68 weeks. However, individual results vary significantly — some people lose more, some less, depending on genetics, lifestyle adherence, and how their body responds.
Both medications are prescribed based on clinical assessment by your GP or a licensed prescriber, who will consider your BMI, health conditions, and medication history. Neither is suitable for everyone — those with a history of thyroid cancer, pancreatitis, or severe gastroparesis may not be eligible. Your prescriber will determine the right starting dose and escalation plan for you. Whichever you're prescribed, combine it with a reduced-calorie diet and increased physical activity for best results.
- 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 difference between Mounjaro and Wegovy doses?
Mounjaro starts at 2.5 mg and goes up to 15 mg weekly (dual GIP+GLP-1 mechanism). Wegovy starts at 0.25 mg and reaches 2.4 mg weekly (GLP-1 only). Mounjaro escalates faster and reaches a higher maximum dose, reflecting its dual action.
Which weight loss injection is stronger, Mounjaro or Wegovy?
Clinical trials show Mounjaro achieves slightly higher average weight loss (20.9% vs 14.9%), but both are effective. "Stronger" depends on how your body responds — individual results vary. Your prescriber will recommend which suits you best after clinical assessment.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible and managed by your prescriber. Approximate dose equivalents exist (e.g. Wegovy 1.7 mg ≈ Mounjaro 10 mg), but any switch must be supervised. Never attempt to switch without medical guidance — your prescriber will manage the transition safely.
How long does it take to reach maximum Mounjaro dose?
Mounjaro escalates every 4 weeks: 2.5 mg (weeks 1–4), 5 mg (5–8), 7.5 mg (9–12), 10 mg (13–16), 12.5 mg (17–20), 15 mg (week 21+). Reaching maximum dose takes approximately 20 weeks if you tolerate each step well.
Do I need an NHS prescription or can I get Mounjaro privately?
In the UK, you can access Mounjaro through NHS specialist tier 3 weight management services (via GP referral) or privately through a GPhC-registered online pharmacy following clinical assessment. NHS waiting lists vary by region; private access is typically faster.
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.