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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Is Wegovy As Effective As Mounjaro For Weight Loss?
Both Wegovy and Mounjaro are prescription-only weight loss injections licensed in the UK, but they work differently and have different effectiveness profiles. Mounjaro (tirzepatide) uses a dual GIP and GLP-1 mechanism, while Wegovy (semaglutide) is a single GLP-1 agonist. Clinical trials show Mounjaro generally produces slightly greater average weight loss, but individual results vary significantly. Both are available through NHS tier 3 specialist services and private prescribing, with eligibility assessed on a personalised basis. This guide explains the real differences in effectiveness between them.
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Calculate Your BMI Instantly
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 Average Weight Loss
Mounjaro (tirzepatide) clinical trials (SURMOUNT-1) showed average weight loss of approximately 15–21% of body weight depending on dose, with the maximum 15 mg dose achieving around 20.9% loss over 72 weeks. Wegovy (semaglutide) trials (STEP-1) showed average weight loss of approximately 14.9% of body weight at the maximum 2.4 mg dose over 68 weeks. Both medications were used alongside a reduced-calorie diet and increased physical activity.
The difference is modest—around 5–6 percentage points on average at maximum doses—but individual outcomes vary considerably. Some people lose significantly more on either medication, whilst others lose less. Your own genetics, starting weight, diet adherence, and activity level are often more influential than which medication you take. Use our GLP-1 weight loss calculator to see projected estimates based on clinical trial averages, though your actual result may differ.
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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
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS Access, Eligibility, And How To Get Prescribed
Both Wegovy and Mounjaro are available through NHS tier 3 specialist weight management services following referral from your GP. Eligibility is the same for both: BMI ≥30, or BMI 27–29.9 with weight-related health conditions. NHS waiting lists vary significantly by region and can be lengthy in many areas. Alternatively, both are available through private UK prescribing following an online clinical assessment with a licensed prescriber. Costs differ between medications and doses, typically ranging from £129–£320 per month. Your prescriber will assess which is most suitable based on your medical history, current medications, and personal circumstances—there is no blanket "best" option for everyone.
- 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 more effective than Wegovy for weight loss?
Clinical trials suggest Mounjaro achieves slightly higher average weight loss (around 5–6% more body weight), but individual results vary significantly. Many people lose similar amounts on either medication. Your personal response depends on genetics, lifestyle, and consistency rather than which one you choose.
How does a Mounjaro KwikPen differ from a Wegovy pen?
Mounjaro uses a reusable KwikPen device with replaceable cartridges containing 4 weekly doses. Wegovy uses pre-filled disposable pens. Both are once-weekly injections. The delivery method doesn't affect effectiveness—it's mainly a practical and cost consideration.
Can I switch from Wegovy to Mounjaro on the NHS?
Potentially, yes, but any medication change requires your prescriber's approval. You cannot switch between medications without guidance. Rough dose equivalence exists—for example, Wegovy 2.4 mg is approximately equivalent to Mounjaro 10–15 mg—but your prescriber will manage any transition safely.
What does NICE guidance say about Mounjaro versus Wegovy?
NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for weight management in adults with obesity or overweight plus comorbidities. Both are considered appropriate options; choice depends on individual clinical assessment, availability, and patient suitability rather than one being recommended over the other.
How long do results take with Wegovy or Mounjaro?
Both typically show noticeable weight loss within 8–12 weeks at effective doses. Doses are increased gradually over 16–20 weeks to reach maximum. Weight loss continues throughout treatment and for several months after stopping, though weight can return if lifestyle habits don't change permanently.
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.