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 Without Subscription — How It Compares to Wegovy
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are available in the UK as prescription-only weight management injections without requiring a subscription. You can access either medication through NHS specialist services or private online prescribing following a clinical assessment. This guide explains the key differences between these dual GIP+GLP-1 and single GLP-1 options, their clinical trial outcomes, and how to determine which might be suitable for you. Individual eligibility depends on your BMI, health conditions, and prescriber assessment.
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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.
Clinical Trial Data and How Each Medication Works
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways simultaneously. In the SURMOUNT-1 clinical trial, participants on the maximum 15mg dose lost an average of 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. The STEP-1 clinical trial showed participants lost approximately 14.9% of their body weight on the maximum 2.4mg dose over 68 weeks with the same lifestyle support. Both medications work by reducing appetite, supporting fullness after smaller meals, and slowing gastric emptying. The dual mechanism in Mounjaro may contribute to slightly greater average weight loss, though individual results vary significantly. Neither medication works in the same way as insulin, and both require a UK prescription following clinical assessment — they are not subscription services.
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.
Doses, Side Effects, and Suitability for You
Mounjaro ranges from 2.5mg to 15mg (once weekly), whilst Wegovy escalates from 0.25mg to 2.4mg (also once weekly). Both medications commonly cause nausea, diarrhoea, constipation, and stomach discomfort, particularly when starting or increasing doses. Side effect profiles are broadly similar. Your prescriber will assess your eligibility based on BMI (30 or above, or 27–29.9 with weight-related health conditions), medical history, and current medications. You can use our free GLP-1 weight loss calculator to estimate potential results at different doses. Neither medication is suitable if you are pregnant, planning pregnancy, or under 18. Some oral contraceptives may be less effective — discuss this with your prescriber. Both require ongoing clinical support and lifestyle changes 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.
Can I get Mounjaro without a monthly subscription in the UK?
Yes. Mounjaro is available as a one-off prescription through NHS specialist services or private online prescribing. You are not locked into a subscription — you can pause or stop at any time following clinical advice. Each KwikPen contains four weekly doses. Pricing and access terms vary by provider.
Is Mounjaro more effective than Wegovy?
Clinical trials show Mounjaro achieved slightly higher average weight loss (20.9% vs 14.9%), but individual results vary considerably. Effectiveness depends on your personal response, adherence to the medication, and lifestyle changes. Your prescriber will recommend whichever is most suitable for your circumstances.
How do I know if Mounjaro or Wegovy is right for me?
A UK-licensed prescriber will assess your BMI, health conditions, medications, and medical history. Both require a clinical assessment before prescription. Use our free BMI calculator to check your starting point, then discuss your options with your GP or a private prescriber to determine eligibility.
What is the difference between tirzepatide and semaglutide?
Tirzepatide (Mounjaro) activates two hormone pathways (GIP and GLP-1), whilst semaglutide (Wegovy) activates only GLP-1. The dual mechanism may support greater appetite suppression and weight loss on average, but both are effective weight management tools when combined with diet and exercise.
Can I switch from Mounjaro to Wegovy if I want to?
Yes, you can switch between medications following prescriber guidance. There is no official conversion chart — your prescriber will manage the transition based on your current dose and response. Switching requires a new prescription and clinical review.
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.