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 Private vs Wegovy — How They Compare
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available privately in the UK. They work through different mechanisms and have different dose schedules. This guide compares the two side-by-side so you can understand the key differences. Both require a clinical assessment before prescription, and individual suitability depends on your personal health profile. Your prescriber will assess which option is most appropriate 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.
How Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways. This dual mechanism may help regulate appetite more effectively by targeting two separate signalling systems in the brain.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating one hormone pathway. Clinical trials showed Wegovy helps participants lose an average of approximately 14.9% of body weight over 68 weeks, whilst SURMOUNT trial data showed Mounjaro achieved average losses of 15–21% depending on dose.
Both are given as once-weekly injections using a KwikPen device. The dual mechanism of Mounjaro does not necessarily mean it is more effective for every individual — results vary significantly between people, and some patients respond better to single-mechanism GLP-1 therapy.
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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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Doses, Side Effects, and Private Access
Mounjaro starts at 2.5 mg and escalates up to 15 mg maximum. Wegovy starts at 0.25 mg and reaches 2.4 mg maximum. Both follow gradual dose escalation over weeks to minimise side effects.
Common side effects for both include nausea, diarrhoea, constipation, and stomach pain — especially during dose escalation. These typically improve over time. Both are available through private online prescribing services in the UK following an online clinical assessment. Neither is currently prescribed on the NHS in routine primary care, though specialist tier 3 weight management services may prescribe them. A UK-licensed prescriber will assess whether you meet eligibility criteria (BMI ≥30 or ≥27 with weight-related health conditions) and determine which medication suits you best.
- 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.
Which is better for weight loss, Mounjaro or Wegovy?
Clinical trials showed both are effective. SURMOUNT data showed Mounjaro achieved 15–21% average weight loss, whilst Wegovy showed approximately 14.9% average loss. However, individual results vary significantly — some people respond better to one than the other. A prescriber will assess which is suitable for your specific health circumstances and preferences.
What is the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist activating two hormone pathways. Wegovy (semaglutide) is a GLP-1 agonist only, activating one pathway. The dual mechanism of Mounjaro does not assures better results — effectiveness depends on individual factors.
Can I switch from Wegovy to Mounjaro privately?
Yes, switching is possible, but it must be managed by your prescriber. There is no official conversion chart — approximate equivalence exists (e.g., Wegovy 2.4 mg ≈ Mounjaro 15 mg), but any switch requires clinical assessment and should follow a gradual tapering and restart protocol.
Are there any differences in side effects between the two?
Both have similar common side effects: nausea, diarrhoea, constipation, and stomach pain. Mounjaro users report these slightly more frequently in trials, possibly because the dual mechanism has a stronger effect. However, side effects typically diminish over time as your body adjusts to each new dose.
How do I access Mounjaro or Wegovy privately in the UK?
Both are available through GPhC-registered online pharmacy services. You complete an online consultation with a UK-licensed prescriber who reviews your health history and determines eligibility based on BMI and health conditions. If approved, a prescription is issued and your medication is dispensed. Costs vary by provider and dose, typically ranging from £129–£320 monthly.
Ready to take control of your weight loss journey?
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