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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Ordering Mounjaro Online vs Wegovy — What's the Difference?
If you're considering ordering Mounjaro or Wegovy online in the UK, understanding how these two prescription-only weight management injections differ is essential. Both are licensed GLP-1-based medications, but they work in different ways and produce different clinical outcomes. This guide compares both medications factually, covering mechanism of action, clinical trial results, dosing, side effects, and how to access them through UK prescribers. Both require a clinical assessment before prescription — individual suitability is determined by a licensed healthcare professional.
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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) is a dual GIP and GLP-1 receptor agonist. It activates two natural hormone pathways simultaneously, which may explain its higher average weight loss in clinical trials. The SURMOUNT-1 trial showed participants lost approximately 15–21% of body weight at the maximum 15 mg dose over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. It activates one hormone pathway. The STEP-1 trial showed participants lost approximately 14.9% of body weight at the maximum 2.4 mg dose over 68 weeks under the same lifestyle conditions.
- Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg weekly
- Wegovy starts at 0.25 mg and escalates to a maximum of 2.4 mg weekly
- Both are once-weekly injections
- Individual results vary significantly — trial averages do not predict personal outcomes
Clinically BackedWeight Loss
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Ordering Online — Access, Side Effects, and Suitability
Both Mounjaro and Wegovy are prescription-only medicines available through UK GPhC-registered online pharmacies following a clinical assessment with a licensed prescriber. Neither medication is available to purchase without a prescription. Common side effects include nausea, diarrhoea, constipation, and stomach pain — these typically decrease over time as your body adjusts.
Which medication suits you depends on individual factors including your medical history, current medications, and how your body responds. A prescriber will assess whether Mounjaro's dual mechanism or Wegovy's single mechanism is more appropriate for you. Try our GLP-1 weight loss calculator to estimate potential outcomes at different doses of either medication, and use our BMI calculator to check your current starting point.
- 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 causes more weight loss — Mounjaro or Wegovy?
Clinical trials show Mounjaro averaged 15–clinically studied weight loss and Wegovy 14.9% at maximum doses. However, individual results vary considerably. Trial averages do not predict personal outcomes. A prescriber assesses which is more suitable based on your individual health profile, not trial averages.
Can I order Mounjaro online without a prescription in the UK?
No. Both Mounjaro and Wegovy are prescription-only medicines in the UK. You must have a prescription from a licensed UK prescriber before any GPhC-registered online pharmacy can dispense either medication. Online pharmacies handle the prescription — they do not replace the clinical assessment requirement.
How long does it take to reach maximum dose with each?
Mounjaro takes approximately 20 weeks to reach 15 mg (4 weeks per dose level). Wegovy takes approximately 16–17 weeks to reach 2.4 mg (similar 4-week escalation per dose). Faster escalation increases side effects without improving efficacy — prescribers follow approved schedules.
What's the cost difference between Mounjaro and Wegovy online?
Costs vary by dose and UK provider but typically range £129–£320 per month depending on dose strength. Mounjaro at 15 mg and Wegovy at 2.4 mg (maximum doses) are usually similar in price. Always check current pricing with your chosen pharmacy — costs change regularly.
How do I know which one I should order?
You cannot choose between them yourself — a prescriber assesses your medical history, medications, and health conditions to recommend the most suitable option. Both require a clinical assessment. Your prescriber will explain why one is preferred for your specific situation rather than the other.
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.