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
15kg Weight Loss: UK Prescription Medication Options
Losing 15kg is a significant health goal, and prescription weight management medication can support your success alongside lifestyle changes. In the UK, several GLP-1 receptor agonist medications are licensed specifically for weight management in adults who meet eligibility criteria. These prescription options work by regulating appetite and supporting sustainable weight loss. Whether you're considering NHS-funded treatment or private prescription options, understanding what's available and how to access it is the first step. Our BMI calculator and weight loss projection tool can help you assess your starting point and explore realistic outcomes with medical support.
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 Weight Loss Medications Explained
Three prescription medications are currently licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections, while Saxenda is a daily injection. All three are GLP-1 receptor agonists (Mounjaro is a dual GIP/GLP-1 agonist) that work by reducing appetite, increasing feelings of fullness, and supporting consistent weight loss when combined with a reduced-calorie diet and increased physical activity.
Clinical evidence shows promising results: in trials, Mounjaro helped participants lose an average of 15–21% of their body weight, while Wegovy supported approximately 14.9% average weight loss. For a 15kg target, this means starting weights of around 70–100kg would be realistic baseline figures. However, individual results vary significantly, and weight loss depends on dose, adherence, and lifestyle changes. A prescriber will assess which medication suits your health profile following a clinical evaluation.
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 vs Private Access: How to Get Started
In the UK, prescription weight loss medication is accessible through two routes. NHS access is through specialist tier 3 weight management services following a GP referral. Availability varies significantly by region, and waiting lists can be lengthy. Private access is through a GPhC-registered online pharmacy following an online clinical assessment with a UK-licensed prescriber—no NHS referral needed.
To find out if you're eligible, calculate your BMI using our free BMI calculator on this page. You'll typically qualify if your BMI is 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. South Asian, Chinese, Black African, or Black Caribbean adults may be eligible at lower BMI thresholds. Start by speaking with your GP about NHS options, or consult a private prescriber if you prefer faster access. Use our GLP-1 weight loss calculator to estimate potential outcomes at different doses.
- 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 with prescription medication?
Clinical trials show Mounjaro and Wegovy support average weight loss of 15–21% of body weight. For a 15kg target, this depends on your starting weight. Results vary—some people lose more, some less. Medication works best alongside a reduced-calorie diet and increased physical activity. A prescriber can give you personalised projections during your clinical assessment.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections licensed for UK weight management. Mounjaro uses dual GIP/GLP-1 technology and may have a slightly higher average weight loss in trials. Wegovy is a GLP-1 agonist only. Both are effective—your prescriber will recommend which suits your health profile best. Individual response varies.
Can I get weight loss medication through the NHS?
Yes, through specialist tier 3 weight management services. You'll need a GP referral. Availability and waiting times vary by region (ICB). Private options via GPhC-registered pharmacies offer faster access without NHS referral. Both require a clinical assessment and prescription from a UK-licensed prescriber.
Am I eligible for prescription weight loss medication?
Generally, yes, if your BMI is 30 or above, or 27–29.9 with weight-related health conditions. Use our free BMI calculator to check. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds. A GP or private prescriber will confirm eligibility following a clinical assessment.
How long does it take to lose 15kg with these medications?
Timeline varies individually. Average weight loss is approximately 0.5–1kg per week on GLP-1 medication (faster than diet alone). A 15kg loss could take 3–6 months depending on starting weight, dose, and adherence. Our weight loss projection calculator can give you a personalised estimate based on your circumstances.
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.