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
Extreme Weight Loss — UK Prescription Options
Before and after photos of extreme weight loss are often circulated online, but they rarely tell the full story. If you're considering significant weight loss, prescription medications such as Mounjaro, Wegovy, and Saxenda are available in the UK for eligible adults. This guide explains how these prescription weight management options work, who qualifies, and how to access them through NHS or private routes. Results vary significantly between individuals, and medication always works alongside diet and physical activity changes.
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.
UK-Licensed Prescription Weight Management Options
Three prescription medications are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — a once-weekly injection that activates dual GIP and GLP-1 pathways. Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, alongside reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection with average weight loss of around 15% of body weight in clinical trials.
- Saxenda (liraglutide) — a once-daily GLP-1 injection, with slightly lower average weight loss outcomes than Wegovy.
All three are prescription-only medicines requiring a clinical assessment before being prescribed. Individual results vary significantly — some people experience greater weight loss than others. These medications are designed to work alongside lifestyle changes, not replace them. Try our free GLP-1 weight loss calculator to explore potential weight loss projections 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.
NHS Eligibility and Access Routes
Eligibility for prescription weight management in the UK:
- BMI of 30 kg/m² or above, or BMI of 27–29.9 with a weight-related health condition (type 2 diabetes, high blood pressure, cardiovascular disease, or sleep apnoea)
- Lower thresholds apply for people of South Asian, Chinese, Black African, or Black Caribbean heritage (BMI 27.5+)
- Must be assessed by a healthcare professional
Access routes: NHS access is through tier 3 specialist weight management services — typically requires GP referral and may involve waiting lists of several months. Private access is available through UK-licensed prescribers following an online clinical assessment. Use our free BMI calculator above to check your BMI and discuss eligibility with your GP or a prescriber.
- 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 prescription weight loss medications assures extreme weight loss?
No. Individual results vary significantly based on genetics, lifestyle adherence, dose, and other factors. Clinical trials show average results, not assured individual outcomes. Medications work best alongside sustained diet and physical activity changes. Your prescriber will discuss realistic expectations based on your health profile.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates dual GIP and GLP-1 pathways, while Wegovy (semaglutide) activates GLP-1 only. Clinical trials suggest Mounjaro may produce slightly higher average weight loss, but individual responses vary. Both are once-weekly injections. Your prescriber will advise which suits your situation.
How long does it take to see weight loss results with GLP-1 medication?
Most people begin noticing appetite changes within the first few weeks, but significant weight loss typically takes 8–12 weeks to become apparent. Clinical trials measured results over 68–72 weeks. Weight loss is gradual — the NHS recommends aiming for 0.5–1 kg per week for sustainable outcomes.
Is prescription weight loss available on the NHS?
Yes, but access varies by region. NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use through specialist tier 3 weight management services. Access requires GP referral and eligibility assessment. Waiting times can be long in many areas. Private options are available without NHS referral.
What happens to weight loss after stopping prescription weight management?
Weight often returns if lifestyle changes are not sustained. These medications are typically used as tools to help establish healthier eating patterns and activity habits. Long-term weight management success depends on maintaining the diet and exercise habits developed during treatment. Discuss long-term plans with your prescriber.
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.