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
Diet and Weight Loss — UK Prescription Options
Weight management in the UK involves both lifestyle changes and, for eligible adults, prescription medication options. The NHS supports weight loss through diet, exercise, and behavioural programmes, but prescription weight loss medications are also available for people who meet specific eligibility criteria. Understanding what's available and how to access support is the first step toward sustainable weight management.
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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
Three prescription medications are currently licensed in the UK for weight management. Mounjaro (tirzepatide) is a once-weekly injection that works by activating two hormone pathways (GIP and GLP-1), helping to reduce appetite and support feeling fuller after meals. Wegovy (semaglutide) is another once-weekly injection that activates the GLP-1 pathway. Saxenda (liraglutide) is a daily injection also using the GLP-1 mechanism.
All three are prescription-only medicines requiring a clinical assessment. In clinical trials, GLP-1 weight loss injections helped participants lose an average of 15–21% of their body weight when combined with a reduced-calorie diet and increased physical activity, though individual results vary significantly. These medications are typically prescribed as part of a comprehensive weight management approach, not as a replacement for lifestyle changes.
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 Access vs Private Options
NHS access: GLP-1 medications are available through specialist tier 3 and tier 4 weight management services. Your GP can refer you if you meet eligibility criteria, which generally include a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. NHS availability varies significantly by region.
Private access: These medications are also available through private prescription following an online clinical assessment with a UK-licensed prescriber. This route typically offers faster access without NHS waiting lists, though costs are borne privately. Either way, a prescriber will assess whether prescription weight management is suitable for your individual health circumstances.
- 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's the difference between diet and weight loss medication?
Diet and lifestyle changes are the foundation of weight management. Prescription weight loss medications support this process by helping to reduce appetite and cravings. They work alongside diet and exercise, not instead of them. Most people using prescription weight loss medication also follow a reduced-calorie diet and increase physical activity for best results.
Who is eligible for prescription weight loss medication in the UK?
Generally, adults with a BMI of 30 kg/m² or above, or 25–29.9 with weight-related health conditions, may be eligible. However, South Asian, Chinese, Black African, and Black Caribbean adults have lower eligibility thresholds due to higher health risks at lower BMI levels. Your GP or a licensed prescriber can assess your eligibility based on your individual health profile.
How quickly can I expect results with weight loss medication?
Clinical trials show an average weight loss of 15–21% of body weight over 68–72 weeks for GLP-1 medications, though this varies significantly between individuals. Sustainable weight loss typically occurs at a rate of 0.5–1 kg per week. Use our free GLP-1 weight loss calculator to see projected results at different doses based on your starting weight.
Can I get prescription weight loss medication on the NHS?
Yes, GLP-1 medications are available through NHS specialist weight management services if you meet eligibility criteria and are referred by your GP. However, availability varies by region and waiting times can be lengthy. Your GP is the best starting point to discuss whether you're eligible and what services are available in your area.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), whilst Wegovy (semaglutide) activates only the GLP-1 pathway. Both are once-weekly injections with similar average weight loss outcomes in clinical trials. Your prescriber will assess which is most appropriate for your individual circumstances and medical history.
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.