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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Wegovy Versus Mounjaro: Key Differences Explained
Both Wegovy and Mounjaro are prescription-only weight loss injections licensed in the UK, but they work differently and have distinct dosing schedules. Wegovy contains semaglutide (a GLP-1 receptor agonist), while Mounjaro contains tirzepatide (a dual GIP and GLP-1 receptor agonist). This guide compares both medications to help you understand how they differ in mechanism, dosing, clinical evidence, side effects, and UK accessibility. Individual results vary significantly, and eligibility depends on your personal health profile assessed by a licensed prescriber.
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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 Wegovy and Mounjaro Work: The Key Difference
Wegovy (semaglutide) activates a single hormone pathway: GLP-1 (glucagon-like peptide-1). This helps signal fullness to the brain, reduces appetite, and slows how quickly food leaves the stomach.
Mounjaro (tirzepatide) activates two hormone pathways: both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. The dual mechanism may offer a more potent appetite-suppressing effect than GLP-1 alone, though clinical evidence shows both medications produce meaningful weight loss.
In the STEP-1 clinical trial, Wegovy helped participants lose an average of approximately 15% body weight. In the SURMOUNT-1 trial, Mounjaro at the maximum dose (15 mg) helped participants lose approximately 21% body weight on average — though individual results vary significantly and outcomes depend on lifestyle changes alongside medication use.
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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 UK Availability
Dosing: Wegovy starts at 0.25 mg weekly and titrates to a maximum of 2.4 mg weekly over 16+ weeks. Mounjaro starts at 2.5 mg weekly and titrates to 15 mg weekly. Both are once-weekly injections given via pre-filled pens (Wegovy auto-injector; Mounjaro KwikPen).
Both medications cause similar side effects: nausea, diarrhoea, constipation, vomiting, and stomach pain are most common. Side effects typically decrease over time as your body adjusts.
UK Access: Both are available through NHS specialist weight management services (tier 3) and private online prescribing following a clinical assessment. Waiting times for NHS tier 3 services vary significantly by region. Private access is available without NHS referral through GPhC-registered pharmacies.
- 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 may produce slightly greater average weight loss (approximately 21% vs 15% in trials), but individual results vary widely. Both are effective; the "better" option depends on your personal health profile and how your body responds. Your prescriber will assess which is more suitable for you.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion dose chart — approximate equivalences exist (e.g., 2.4 mg Wegovy ≈ 15 mg Mounjaro), but any switch requires medical supervision to ensure safe transition.
What's the difference between Mounjaro and Ozempic?
Both contain the same active ingredient (semaglutide), but Ozempic is licensed for type 2 diabetes (up to 2 mg dose) and Mounjaro is the licensed weight management version. Using Ozempic for weight loss is off-label. Wegovy is the licensed semaglutide weight loss injection in the UK.
How long do you stay on Wegovy or Mounjaro?
There is no fixed end date. These are typically long-term medications — you continue as long as they are effective and tolerated. If you stop, weight loss often regresses gradually. Your GP or prescriber will review your ongoing need regularly and discuss sustainability with you.
Which injection is available faster on the NHS in the UK?
Both Mounjaro and Wegovy availability on the NHS depends on your local ICB (integrated care board) and specialist tier 3 weight management service. Waiting times vary significantly by region — some areas have months-long waiting lists. Private access is typically faster, though at personal cost.
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.