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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Ketogenic Diet and Weight Loss — UK Prescription Options
The ketogenic diet is a low-carbohydrate eating approach that some people use for weight management, but it's not the only option available in the UK. For adults struggling with weight management, prescription medications like Mounjaro and Wegovy offer evidence-based support alongside lifestyle changes. This guide explores how ketogenic approaches compare to medication options, who may be eligible for prescription weight loss treatment on the NHS, and how to find out if these options are right for you.
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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 and How They Work
For adults seeking weight management in the UK, prescription medications are available alongside dietary approaches like the ketogenic diet. Three main options are licensed for weight loss: Mounjaro (tirzepatide), a dual GIP and GLP-1 receptor agonist with clinical evidence showing average weight loss of 15–21% of body weight; Wegovy (semaglutide), a GLP-1 receptor agonist with clinical trials demonstrating approximately clinically studied weight loss on average; and Saxenda (liraglutide), a daily injection option. These prescription weight loss medications work by reducing appetite, supporting fullness after meals, and helping regulate blood sugar. They are most effective when combined with reduced-calorie eating and increased physical activity—similar principles to structured dietary approaches. Individual results vary significantly, and eligibility depends on BMI and health conditions. You can use our free GLP-1 weight loss calculator to explore potential weight loss at different treatment doses, and our BMI calculator to check whether you may fall within eligibility thresholds.
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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
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NHS Access vs Private Options — How to Find Out If You're Eligible
Weight loss medication on the NHS is available through specialist tier 3 weight management services, typically following referral from your GP. Eligibility generally includes adults with a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. NHS access varies significantly by region and can involve waiting lists. Alternatively, prescription weight loss in the UK is available privately through licensed online prescribers following a clinical assessment—no NHS referral required. Your first conversation should be with your GP, who can discuss all available options, assess your personal health circumstances, and advise whether medication is appropriate for you. They can also discuss how dietary approaches like ketogenic eating fit alongside any medical treatment you may pursue.
- 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 does the ketogenic diet compare to weight loss medication like Mounjaro?
The ketogenic diet is a dietary approach that restricts carbohydrates to encourage fat metabolism. Mounjaro and similar medications work by reducing appetite and supporting blood sugar control. Both can support weight loss but operate differently—one through diet change, one through hormone signalling. Many people use structured diets alongside medication for better results. Your GP can advise which approach suits your individual circumstances.
Am I eligible for prescription weight loss medication on the NHS?
NHS weight loss medication eligibility generally requires a BMI of 30 or above, or 27 or above with a weight-related health condition like diabetes or hypertension. Eligibility also differs for people of South Asian, Chinese, Black African, or Black Caribbean heritage, with lower BMI thresholds applied. Speak to your GP for a personalised assessment of your eligibility.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates dual GIP and GLP-1 hormone pathways, whilst Wegovy (semaglutide) activates GLP-1 only. Mounjaro clinical trials showed slightly higher average weight loss (15–21% vs 15%), but individual results vary considerably. Both are once-weekly injections and available on the NHS through specialist services or privately. Your prescriber will advise which is more suitable.
How quickly can I expect weight loss with prescription medication?
Weight loss with Mounjaro or Wegovy typically begins after 2–4 weeks, with more noticeable changes over 12–16 weeks. The NHS recommends sustainable weight loss of 0.5–1 kg per week. Clinical trials measured weight loss over 68–72 weeks. Results vary based on dose, adherence, and lifestyle changes. Use our weight loss calculator to see projected timelines.
Can I use the ketogenic diet alongside weight loss medication?
Prescription weight loss medications work best alongside reduced-calorie eating and physical activity—dietary structure is part of the treatment plan. The ketogenic diet is one approach, though your prescriber may recommend different dietary guidance. Always discuss your dietary plan with your GP or prescriber to ensure it complements any medication safely.
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.