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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Achieving 4kg Weight Loss with UK Prescription Medication
Losing 4kg is a realistic and achievable goal that can significantly improve your health markers and quality of life. In the UK, several prescription weight management medications are now available to eligible adults, helping support weight loss alongside diet and exercise. This guide explains how prescription options work, who qualifies, and how to access them through both NHS weight management services and private prescribing.
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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 Medications Available
Three prescription-only medications are currently licensed in the UK for weight loss in eligible adults: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These are GLP-1 receptor agonist medications (or in Mounjaro's case, a dual GIP/GLP-1 agonist) that work by helping reduce appetite, support feeling fuller after smaller meals, and regulate blood sugar control.
Clinical evidence: In trials, Mounjaro helped participants lose an average of 15–21% of body weight over time, whilst Wegovy supported losses of around 15% on average. Individual results vary significantly depending on dose, adherence, diet, and exercise. A 4kg loss represents meaningful progress that, alongside lifestyle changes, can improve blood pressure, cholesterol, and blood sugar control.
- Mounjaro: Once-weekly injection, doses 2.5–15mg
- Wegovy: Once-weekly injection, doses 0.25–2.4mg
- Saxenda: Once-daily injection, doses 0.6–3mg
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 in the UK
You may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds apply for people of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower weights.
NHS access: Referral to a specialist tier 3 weight management service through your GP. Availability and waiting times vary by region. Private access: Online consultation with a UK-licensed prescriber; prescription dispensed by a GPhC-registered pharmacy without NHS referral. Use our free BMI calculator above to check your personal BMI, and our GLP-1 weight loss calculator to explore potential outcomes at different doses. Start a conversation with your GP about whether prescription support is right for you.
- 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.
Will a prescription medication assures I lose 4kg?
No medication assures weight loss. Clinical trials show average results, but individual outcomes vary based on dose, lifestyle changes, adherence, genetics, and metabolism. Medications work best alongside a reduced-calorie diet and increased physical activity. Your GP can discuss realistic expectations for you personally.
How quickly can I lose 4kg with Mounjaro or Wegovy?
The NHS recommends losing 0.5–1kg per week for sustainable results. At this rate, 4kg would take 4–8 weeks. However, prescription medications may help achieve this within 8–12 weeks depending on your starting weight, dose, and lifestyle. Results vary between individuals.
Can I get Mounjaro or Wegovy through the NHS for 4kg weight loss?
NHS prescription weight loss medication is typically available through specialist tier 3 weight management services, and access varies significantly by region and local availability. You would need a GP referral. Private online prescribing is another route if you meet clinical eligibility criteria. Contact your GP to discuss what's available locally.
What's the difference between Mounjaro and Wegovy for weight management?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs 15%), but individual results vary. Both are once-weekly injections. A prescriber can help determine which is more suitable for you.
How can I work out my personal BMI and track a 4kg weight loss goal?
Use our free BMI calculator above to check your current BMI instantly. It will show you where you stand against NHS healthy weight ranges. After achieving 4kg loss, use our progress tracker to log your results, monitor improvements in your BMI, and celebrate your progress toward your health goals.
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.