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
Tips for Taking Mounjaro and Wegovy — A Comparison
If you're considering Mounjaro or Wegovy for weight management in the UK, understanding how to use each injection safely and effectively is essential. Both are prescription-only GLP-1 receptor agonist medications, but they differ in their mechanisms, dosing schedules, and how they're administered. This guide compares practical tips for taking each medication, the clinical evidence from trials, and how your prescriber will help you choose which is right for your individual health needs. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses.
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 Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways rather than one. This dual mechanism may help regulate appetite, reduce cravings, and support feeling fuller after meals more effectively for some people. Wegovy (semaglutide) works as a GLP-1 receptor agonist only, activating a single hormone pathway. Clinical trial data shows both medications support weight loss: SURMOUNT-1 trials showed Mounjaro helped participants lose an average of 15–21% of body weight, whilst STEP-1 trials showed Wegovy helped participants lose approximately 15% of body weight on average. Individual results vary significantly based on lifestyle changes, adherence, and individual response.
- Mounjaro: once-weekly injection, doses from 2.5 mg to 15 mg
- Wegovy: once-weekly injection, doses from 0.25 mg to 2.4 mg
- Both require a minimum of 4 weeks on each dose before increasing
- Both are administered via pre-filled pen devices
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.
Practical Tips and Suitability — Prescriber Decision
Both Mounjaro and Wegovy are prescription-only medicines requiring a clinical assessment before being prescribed. Your prescriber will consider your individual health history, current medications, BMI, and any weight-related health conditions to determine which medication is more suitable for you. Neither medication is "better" — suitability depends on your personal circumstances. Use our free BMI calculator to assess your starting point, then discuss results with your GP or a licensed prescriber. Common tips for both medications include: rotating injection sites weekly (stomach, thigh, or upper arm), storing unopened pens in the refrigerator at 2–8°C, and taking time to adjust to initial side effects like nausea, which often improve within the first few weeks. Always take your medication alongside a reduced-calorie diet and increased physical activity for best results.
- 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.
What's the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist activating two hormone pathways, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Both are once-weekly injections, but they have different maximum doses and come from different manufacturers. Both support weight loss when used alongside diet and exercise.
Which injection causes fewer side effects — Mounjaro or Wegovy?
Both medications can cause similar side effects including nausea, diarrhoea, and stomach pain — especially during dose escalation. Individual tolerance varies greatly. Your prescriber will monitor you and adjust your dose if side effects are problematic. Most side effects improve over time.
How do I know which medication my GP will prescribe?
Your prescriber will assess your individual health, medical history, BMI, and any weight-related conditions. Neither medication is automatically "right" for everyone. A clinical assessment will determine suitability. You can discuss preferences with your prescriber, but the final decision is based on clinical appropriateness.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official established conversion chart between tirzepatide and semaglutide doses — any switch requires a clinical decision and new prescription. Do not stop one and start another without guidance.
Do I need to follow a specific diet while taking either injection?
Yes. Both Mounjaro and Wegovy work best alongside a reduced-calorie, balanced diet and increased physical activity. Your prescriber or a dietitian can advise on a suitable eating plan. Track your progress using our free progress tracker to stay motivated throughout your weight loss journey.
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.