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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Fibre Diet Weight Loss and UK Prescription Options
A high-fibre diet can support weight loss by helping you feel fuller for longer, but for some people, prescription weight management medication may also be appropriate. In the UK, several medications are available to support weight loss alongside dietary changes like increasing fibre intake. This guide explains the prescription weight loss options available through the NHS and privately, who may be eligible, and how to discuss these with your GP.
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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 for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Both Mounjaro and Wegovy work as GLP-1 receptor agonists (or in Mounjaro's case, a dual GIP and GLP-1 agonist), helping to regulate appetite and reduce food cravings. In clinical trials, these medications helped participants lose an average of 15–21% of their body weight when used alongside a reduced-calorie diet and increased physical activity—though individual results vary significantly. Saxenda is a daily injection, while Mounjaro and Wegovy are both once-weekly injections. All three are prescription-only medicines and require a clinical assessment before being prescribed. They work best when combined with lifestyle changes, including a balanced diet rich in fibre, vegetables, and whole grains.
Clinically BackedWeight Loss
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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 and Private Options
In the UK, prescription weight loss medication is available through two routes. Through the NHS, medications are typically prescribed by specialist tier 3 weight management services following a GP referral—availability and waiting times vary significantly by region. Privately, UK-licensed prescribers can assess your eligibility through online consultations, with prescriptions dispensed by GPhC-registered pharmacies. To check if you may be eligible, use our free BMI calculator above—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, may qualify. Your GP can discuss which route and medication might suit your health goals.
- 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.
Can I lose weight with fibre alone, or do I need medication?
A high-fibre diet is an excellent foundation for weight loss and can help significantly on its own. Eating more vegetables, whole grains, and legumes helps you feel fuller longer and supports a calorie deficit. However, if you have tried dietary changes and would benefit from additional support, prescription weight loss medication may be appropriate. Your GP can assess your individual situation.
How does prescription weight loss medication work with a fibre-rich diet?
Medications like Mounjaro and Wegovy help reduce appetite and regulate hunger signals, which makes it easier to stick to a healthy, fibre-rich eating plan. They are not a replacement for diet and exercise but a tool that can make it easier to maintain the lifestyle changes needed for sustainable weight loss.
Am I eligible for weight loss medication on the NHS?
NHS prescription weight loss medication is available to adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Regional variation exists, so eligibility and availability depend on your local integrated care board. Your GP can refer you to specialist weight management services if appropriate.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections licensed for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist and may produce slightly higher average weight loss. Wegovy (semaglutide) is a GLP-1 agonist only. Both are effective; your prescriber will recommend the most suitable option based on your health.
How quickly will I lose weight on prescription medication?
Individual results vary, but clinical trials show average weight loss of 15–21% over approximately 16–20 weeks on maximum doses. Weight loss continues if you remain on the medication alongside lifestyle changes. The NHS recommends a sustainable loss of 0.5–1 kg per week, and gradual weight management requires medical supervision.
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.