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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3 Stone Weight Loss: UK Prescription Medication Options
Losing 3 stone (42 pounds or approximately 19 kg) is a significant health goal that many UK adults pursue. If you're considering prescription weight management options, several medications are now available through the NHS and private healthcare. This guide explains which prescription weight loss medications are licensed in the UK, how they work, who is eligible, and how to find out if medical support might be right for you.
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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 Prescription Weight Loss Medications
Three prescription-only medications are currently licensed in the UK for weight management in adults. Mounjaro (tirzepatide) is a once-weekly injection that activates dual GIP and GLP-1 hormone pathways, helping to reduce appetite and support feeling fuller after meals. Clinical trials showed that participants lost an average of 15–21% of their body weight — though individual results vary significantly. Wegovy (semaglutide) is also a once-weekly injection and works as a GLP-1 receptor agonist; trials demonstrated average weight loss of around 15% of body weight. Saxenda (liraglutide) is a daily injection with similar GLP-1 mechanisms.
All three are prescription-only medicines requiring a clinical assessment before being prescribed. Eligibility typically includes adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher health risks at lower weights.
To understand your personal weight loss target in health context, use our free BMI calculator to see where you currently stand and what a healthy weight range looks like for your height.
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 and Next Steps
In the UK, weight loss medication is available through two routes. The NHS prescribes these medications through specialist tier 3 weight management services — typically accessed via GP referral. However, NHS availability varies significantly by region, and waiting lists can be lengthy in many areas. Private online prescribing services offer faster access; you complete a clinical assessment with a UK-licensed prescriber, and if approved, the medication is dispensed by a GPhC-registered pharmacy.
To find out if prescription weight loss medication is right for you, start with a conversation with your GP. They can assess your health, discuss whether you meet eligibility criteria, and explain your options. You can also use our free GLP-1 weight loss calculator to project potential results at different doses — this can help inform your discussion with your healthcare provider.
Track your progress throughout your weight loss journey with our free progress tracker, which allows you to log weight changes and monitor your path towards your 3 stone target.
- 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 expect to lose with prescription weight loss medication?
Individual results vary significantly. Clinical trials show average weight loss of 15–21% of body weight depending on the medication and dose. For a person weighing 100 kg, this might mean losing 15–21 kg. However, results depend on your starting weight, adherence to medication, diet, physical activity, and individual metabolism. Your prescriber can discuss realistic expectations for you personally.
Am I eligible for weight loss medication on the NHS?
Generally, you may be eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions (diabetes, high blood pressure, sleep apnoea, etc.). For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds may apply. Eligibility is assessed individually by your GP or a specialist service. Start by speaking with your GP about referral to a tier 3 weight management service.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections, but Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials suggest slightly higher average weight loss with Mounjaro (15–21% vs 15%), though this varies between individuals. Saxenda is a daily injection with similar GLP-1 mechanisms. Your prescriber will help determine which suits you best based on your health, preferences, and lifestyle.
How long does it take to lose 3 stone?
The timeline depends on the medication, dose, your individual response, diet, and activity level. If losing at a sustainable rate of 0.5–1 kg per week (NHS recommendation), losing 19 kg might take 4–6 months. With medication, some people lose faster, particularly in the first 3 months. However, gradual weight management increases muscle loss risk. Your healthcare provider can give you a personalised timeline based on your starting point and medical history.
Can I get weight loss medication privately if I'm not eligible for the NHS?
Yes. Private online prescribing services assess you independently of NHS criteria. You complete a clinical consultation with a UK-licensed prescriber who evaluates your health, medications, and suitability. If approved, you receive a prescription dispensed by a GPhC-registered pharmacy. Costs vary by medication, dose, and provider (typically £129–£320+ monthly), and treatment is private pay. Always check the prescriber is registered with the General Medical Council (GMC).
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.