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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Clean Weight Loss: UK Prescription Options
Clean weight loss means losing weight safely and sustainably through evidence-based methods. In the UK, prescription weight management medications are available for eligible adults alongside lifestyle changes. These aren't quick fixes or supplements — they're prescription-only medicines approved by the MHRA that work with your body's natural hormones to support weight management. If you're interested in prescription weight loss, understanding what's available and whether you're eligible is the first step toward informed decisions about your health.
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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 weight management medications are currently licensed in the UK for adults with excess weight:
- Mounjaro (tirzepatide) — a once-weekly injection that works on two hormone pathways (GIP and GLP-1). In clinical trials, participants lost an average of 15–21% of their body weight alongside diet and exercise changes.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Clinical trial data showed average weight loss of around 15% of body weight over 68 weeks.
- Saxenda (liraglutide) — a daily GLP-1 injection. This was the first GLP-1 medication licensed for weight management in the UK.
All three are prescription-only and require a clinical assessment before being prescribed. Eligibility typically means a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply — your GP can advise on this.
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, you can access prescription weight management through two routes:
- NHS: Referral to a tier 3 specialist weight management service from your GP. Availability varies significantly by region, and waiting times can be lengthy in some areas.
- Private: Online consultation with a UK-licensed prescriber, available without NHS referral. This route is faster but involves private costs.
Regardless of route, clean weight loss with medication works best alongside reduced-calorie diet and increased physical activity. Your first step is always a conversation with your GP about whether this approach is suitable for you, your health history, and what's available in your area. A GP can also help you understand weight management in the context of your personal BMI and health risks.
- 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.
What makes weight loss "clean" in the UK health context?
Clean weight loss means losing weight safely and sustainably through evidence-based methods — typically a combination of diet, physical activity, and where appropriate, prescription medication. It's not about crash diets or unproven supplements. In the UK, GLP-1 and GIP/GLP-1 medications are evidence-based options licensed by the MHRA specifically for weight management. Individual results vary, but clinical trials show average weight loss of 15–21% of body weight over several months.
Am I eligible for prescription weight loss medication on the NHS?
Generally, you may be eligible 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, high blood pressure, or sleep apnoea). Lower thresholds apply for certain ethnic groups. However, NHS availability varies significantly by region — your GP can assess your eligibility and discuss what's available in your area through specialist services.
How do I know if prescription weight loss is right for me?
The best way is to speak with your GP. They'll assess your health history, current weight and BMI, any existing medical conditions, and medications you take. Use our free BMI calculator to understand your current BMI category, which gives you a starting point for that conversation. Your GP can then discuss whether prescription options are appropriate and what route of access (NHS or private) suits your circumstances.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections licensed for weight management in the UK. Mounjaro (tirzepatide) works on two hormone pathways (GIP and GLP-1), while Wegovy (semaglutide) works on one (GLP-1). In clinical trials, Mounjaro showed average weight loss of 15–21%, slightly higher than Wegovy's 15%. However, individual results vary significantly. Your prescriber will help determine which is most suitable based on your health profile.
Can I track my weight loss progress while using prescription medication?
Absolutely. Monitoring your weight regularly helps you and your healthcare provider assess how well the medication is working alongside your lifestyle changes. Our free progress tracker lets you log your weight over time and see your trends visually. Aim to weigh yourself weekly at the same time of day for consistency. Remember that weight loss is not always linear — fluctuations are normal and don't mean the medication isn't working.
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.