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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20 Lb Weight Loss: UK Medication Options and What to Expect
Losing 20 lb (approximately 9 kg) is a realistic goal for many UK adults, especially with proper support. Whether you're looking to improve your health or reach a healthier weight, prescription weight management medications can help alongside diet and lifestyle changes. This guide explains the UK-licensed options available, who is eligible, and how to access them through the NHS or privately. Use our free BMI calculator to check where you currently stand, and our GLP-1 weight loss calculator to explore potential outcomes with medication support.
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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 Management Medications
Three prescription-only medications are licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All are GLP-1 receptor agonists (or dual GIP/GLP-1 agonists in Mounjaro's case) that reduce appetite and help you feel fuller after eating.
Clinical evidence: In trials, these medications helped participants lose an average of 14–21% of body weight — though individual results vary. For a 14-stone (89 kg) adult, a 20% reduction would represent significant progress. Each medication is prescribed at increasing doses over weeks, with regular monitoring by a healthcare professional.
- Mounjaro: Once-weekly injection, dual mechanism, doses up to 15 mg
- Wegovy: Once-weekly injection, GLP-1 only, maximum dose 2.4 mg
- Saxenda: Once-daily injection, GLP-1 only, maximum dose 3 mg
All require a prescription and clinical assessment before being prescribed. Use our GLP-1 weight loss calculator to estimate potential progress at different doses.
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.
Eligibility and How to Access Treatment in the UK
To be eligible for prescription weight loss medication in the UK, you generally need a BMI of 30 or above, or 27 or above if you have a weight-related health condition (type 2 diabetes, high blood pressure, sleep apnoea, or cardiovascular disease). Check your BMI using our free BMI calculator above.
NHS access: Request a referral from your GP to a specialist weight management service (tier 3). NHS availability varies by region and waiting times can be lengthy.
Private access: Available through GPhC-registered online clinics following an online consultation with a UK-licensed prescriber. This route doesn't require NHS referral. Your GP can advise whether medication is appropriate for you, regardless of which route you choose.
- 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.
How much weight can I realistically lose in 20 weeks with prescription medication?
Based on clinical trials, many people lose 10–20% of their body weight over 16–20 weeks on GLP-1 medication. For someone weighing 89 kg (14 st), this could mean losing 9–18 kg. However, individual results vary significantly and depend on your starting weight, dose reached, diet, and exercise. Our weight loss calculator can provide a personalised estimate based on your circumstances.
Is 20 lb weight loss safe and realistic?
Yes, losing 20 lb (9 kg) is a safe and realistic goal. The NHS recommends weight loss of 0.5–1 kg per week for sustainable results. At this rate, 20 lb could take 8–18 weeks depending on your approach. Prescription medications can accelerate this when combined with diet and exercise changes. Always discuss your target with your GP.
What's the difference between Mounjaro, Wegovy, and Saxenda?
Mounjaro is a dual GIP and GLP-1 agonist (newer mechanism) with once-weekly dosing up to 15 mg. Wegovy and Saxenda both target GLP-1 only — Wegovy is once-weekly up to 2.4 mg, while Saxenda is once-daily up to 3 mg. Mounjaro has shown slightly higher average weight loss in trials. Your prescriber will determine which is most suitable for you.
Can I get weight loss medication through the NHS?
Yes, but NHS access is typically through specialist tier 3 weight management services, not standard GP prescription. You need a referral from your GP and may face a waiting list. Availability varies significantly by region (ICB). Private clinics offer faster access through online consultation, though you'll pay privately. Ask your GP about options in your area.
Do I need to change my diet if I'm taking weight loss medication?
Yes. Prescription weight management medications work best alongside a reduced-calorie diet and increased physical activity. Medication reduces appetite and cravings, but sustainable weight loss still requires lifestyle changes. Many people find it easier to follow a healthier diet while on medication. Your healthcare team can provide dietary support and guidance.
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.