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 vs Wegovy: Which Weight Loss Peptide Is Right for You?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but they work differently and produce different results. Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy targets GLP-1 only. This guide compares both medications factually, including clinical trial data, eligibility, and how your prescriber will assess which is suitable for you. Individual results vary significantly, and both require a clinical assessment before prescription.
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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 — Mechanism and Trial Data
Mounjaro (tirzepatide) activates two hormone pathways simultaneously: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. This dual mechanism may enhance appetite suppression and metabolic effects. In the SURMOUNT-1 clinical trial, participants taking the maximum 15 mg dose lost an average of approximately 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) activates GLP-1 receptors only, using a single mechanism. In the STEP-1 clinical trial, participants on the maximum 2.4 mg dose achieved an average weight loss of approximately 14.9% of body weight over 68 weeks under the same lifestyle conditions.
- Mounjaro starting dose: 2.5 mg weekly; maximum: 15 mg weekly
- Wegovy starting dose: 0.25 mg weekly; maximum: 2.4 mg weekly
- Both require 4-week minimum intervals between dose increases
- Both are once-weekly injections using pre-filled pen devices
Clinical trial averages do not assures individual outcomes. Use our GLP-1 weight loss calculator to explore projected results at different doses based on clinical evidence.
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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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Eligibility, Side Effects, and How Your Prescriber Decides
UK eligibility for both medications is identical: a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. People of South Asian, Chinese, Black African, or Black Caribbean heritage may have lower thresholds (BMI 27.5+). Both medications carry similar common side effects including nausea, diarrhoea, constipation, and vomiting—typically improving as your body adjusts.
Your prescriber will assess your individual health, medical history, and preferences to determine which is suitable for you. Neither medication is inherently "better"—suitability depends on your personal circumstances, response, and tolerability. Both require prescription and can be accessed through NHS specialist weight management services or private online prescribing following a clinical assessment. Track your progress using our free progress tracker once you begin 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.
Is Mounjaro better than Wegovy?
Clinical trials show Mounjaro achieved slightly higher average weight loss (20.9% vs 14.9%), but individual results vary widely. "Better" depends on your personal response, tolerability, and suitability assessed by your prescriber. Both are prescription-only and require clinical assessment.
Can I switch from Wegovy to Mounjaro?
Your prescriber may recommend a switch if Wegovy isn't working or causing side effects. Approximate dose equivalences exist (0.5 mg Wegovy ≈ 5 mg Mounjaro), but any switch must be managed by your healthcare provider—never self-manage dose transitions.
How do I know which one to try first?
Your GP or prescriber will assess your health, medication history, and preferences. Some may suggest starting with Wegovy (lower starting dose) and escalating if tolerable; others may recommend Mounjaro directly. Clinical assessment determines the best choice for you individually.
Do Mounjaro and Wegovy work if I don't diet or exercise?
Both medications work best alongside a reduced-calorie diet and increased physical activity—as shown in clinical trials. They are tools to support lifestyle changes, not replacements for them. Sustainable weight loss requires both medication and behaviour change.
Where can I get Mounjaro or Wegovy in the UK?
Both are available through NHS specialist weight management services (tier 3) following GP referral, or through private online prescribing following a clinical assessment. NHS access varies by region; private access is more immediate but involves costs. Check availability in your area with your GP. ```
Ready to take control of your weight loss journey?
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