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
Free tracker included with every download this week
Mounjaro vs Wegovy — A Belfast Guide to Both Weight Loss Injections
If you're in Belfast exploring weight loss options, you may have heard about both Mounjaro and Wegovy. Both are prescription-only GLP-1 based weight management injections available in the UK, but they work differently and suit different people. This guide compares the two fairly, explains how they differ, and helps you understand what to discuss with your prescriber. Use our free GLP-1 weight loss calculator to see potential outcomes at different doses for either medication.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
How Mounjaro and Wegovy Work — The Key Difference
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one hormone pathway (GLP-1) to reduce appetite and support feeling fuller after smaller meals.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways at once. This dual mechanism may offer different effects on appetite control and fat utilisation.
In clinical trials, SURMOUNT data showed Mounjaro achieved average weight loss of around 15–21% of body weight, whilst STEP trials showed Wegovy achieved approximately 14.9% average loss at the maximum dose. Both results came alongside reduced-calorie diet and increased physical activity. Individual results vary significantly — neither medication assures specific outcomes.
Both require a KwikPen injection once weekly. Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg. Wegovy starts at 0.25 mg and escalates to 2.4 mg maximum.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Which Medication Might Suit You — A Prescriber Decision
Eligibility for both Mounjaro and Wegovy in Belfast is the same: you need a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Both are prescription-only and require a clinical assessment.
Your prescriber will assess your medical history, current medications, and personal health goals to determine which is more suitable for you. Some people respond better to one mechanism than the other — this is individual. Both carry similar side effects (nausea, diarrhoea, constipation, stomach pain), though severity and duration vary. Track your progress with our free progress tracker once you start treatment. Neither medication should replace diet and exercise — both work best alongside lifestyle changes.
- 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 available on the NHS in Belfast?
Mounjaro is approved by NICE for NHS weight management services, but availability varies across Northern Ireland trusts. Access is typically through specialist tier 3 weight management services. Waiting lists can be long. Your GP can refer you, or you can access private prescription through a licensed UK prescriber.
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 established conversion chart. Approximate equivalence exists (5 mg Mounjaro ≈ 0.5 mg Wegovy; 15 mg Mounjaro ≈ 2.4 mg Wegovy), but your prescriber will personalise the switch based on your response and tolerance.
Which injection is less likely to cause nausea?
Both carry similar nausea risk — it's very common in the first few weeks. Nausea typically improves over time. Slow dose escalation (staying 4 weeks on each dose) helps. Individual tolerance varies, so what one person experiences may differ from another. Your prescriber can advise on managing side effects.
How do I access either medication in Belfast?
NHS access is through referral to a specialist weight management service (waiting times vary). Private access is through online consultation with a UK-licensed prescriber and GPhC-registered pharmacy — available without NHS referral. Both routes require clinical assessment and a valid prescription.
Do I need to use the GLP-1 calculator before starting either medication?
Our free GLP-1 weight loss calculator helps you estimate potential outcomes at different doses — it's useful for understanding expectations before your prescriber appointment. However, the calculator is educational only. Your prescriber will assess your individual suitability and prescribe based on clinical judgment, not calculator results.
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.