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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Best Injection For Losing Weight in the UK
If you're considering prescription weight loss injections, there are several licensed options available in the UK. The most commonly prescribed weight loss injections are Wegovy (semaglutide) and Mounjaro (tirzepatide), both prescription-only medicines that work by mimicking natural hunger-regulating hormones. Both have strong clinical trial evidence supporting their effectiveness, though which is "best" depends on your individual health circumstances, medical history, and how your body responds. This guide covers the main options available through UK pharmacies and the NHS, so you can understand what to expect before speaking to your GP or a licensed prescriber.
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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.
UK-Licensed Weight Loss Injections: What's Available
The UK has approved three prescription-only injectable medications specifically for weight management: Wegovy (semaglutide), Mounjaro (tirzepatide), and Saxenda (liraglutide). Wegovy and Mounjaro are the most widely prescribed. Wegovy is a once-weekly GLP-1 receptor agonist that activates a single hormone pathway to reduce appetite and promote feeling fuller after meals. Mounjaro, also once-weekly, is a dual GIP/GLP-1 agonist — it activates two hormone pathways, which may explain slightly higher average weight loss in clinical trials. Saxenda is a daily injection, making it less convenient for most people. All three require a prescription from a licensed UK prescriber and an assessment to confirm eligibility. Use our GLP-1 weight loss calculator to estimate potential results at different doses, and our BMI calculator to check whether you meet typical eligibility criteria (BMI 30 or above, or 27–29.9 with weight-related health conditions).
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.
Clinical Evidence: Weight Loss Results and Sustainability
Clinical trials show that prescription weight loss injections deliver meaningful, sustained results when used alongside a reduced-calorie diet and increased physical activity. In the STEP-1 trial, Wegovy helped participants lose an average of approximately 15% of their body weight over 68 weeks. Mounjaro showed slightly higher average weight loss of 15–21% in the SURMOUNT-1 trial, though individual results vary significantly. Both injections work best as part of a comprehensive weight management approach, not as a standalone solution. Most people continue to lose weight for 12–18 months, then weight stabilises if the injection is maintained. If you stop the injection, weight often returns over time, so long-term use is typically needed. Track your progress with our free progress tracker to monitor your own results and stay motivated.
- 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 Wegovy or Mounjaro the best weight loss injection?
Neither is objectively "best" — it depends on your individual health, medical history, and how your body responds. Mounjaro showed slightly higher average weight loss in trials (15–21% vs 15%), but Wegovy has longer clinical track record. Your prescriber will recommend the most suitable option for you based on eligibility, contraindications, and personal factors.
Can I get weight loss injections on the NHS?
Yes, but availability varies significantly by region. Access is through specialist tier 3 weight management services, usually after referral from your GP. NHS waiting lists can be very long (months to years in some areas). Private prescribing through online clinics is faster but involves cost (typically £129–£320 per month depending on dose).
What's the difference between Ozempic and Wegovy?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (doses up to 2mg) and Wegovy is licensed specifically for weight management (doses up to 2.4mg). Ozempic is not approved for weight loss in the UK, though it's sometimes used off-label. Wegovy is the correct licensed option for weight loss.
How much weight can I realistically lose with injections?
Clinical trials show average weight loss of 15–21% of body weight over 12–18 months, alongside lifestyle changes. However, individual results vary considerably — some people lose more, some less. Your prescriber will discuss realistic expectations based on your starting weight and health status.
Do I need to change my diet and exercise if I take weight loss injections?
Yes. Prescription weight loss injections are most effective when combined with a reduced-calorie diet and increased physical activity. The injection supports these efforts by reducing appetite and cravings, but sustainable weight loss requires behaviour change alongside medication.
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.