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 Weight Loss and UK Prescription Medication
Ketogenic diets can support weight loss for some people, but combining dietary approaches with prescription weight management medication may offer additional support for eligible adults in the UK. If you're considering both a ketogenic approach and medical weight management, understanding the prescription options available through the NHS and privately is important. This guide covers the licensed weight management medications available in the UK, who may be eligible, and how to discuss your options with your GP.
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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 Prescription Weight Management Options
Three prescription medications are currently licensed in the UK for weight management, offering different mechanisms of action for eligible adults:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist given as a once-weekly injection. In clinical trials, participants lost an average of 15–21% of their body weight when combined with lifestyle changes. Starting dose is 2.5 mg, with a maximum dose of 15 mg weekly.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, also given once weekly. Clinical trials showed average weight loss of approximately 15% of body weight. Doses range from 0.25 mg to 2.4 mg weekly.
- Saxenda (liraglutide) — a daily GLP-1 injection with similar efficacy to Wegovy. Given as a once-daily injection with a maximum dose of 3 mg.
All three work by helping reduce appetite, support feeling fuller after meals, and support weight management through altered hunger signals. Individual results vary significantly, and these medications work best alongside a reduced-calorie diet and increased physical activity — whether that includes a ketogenic approach or another dietary method.
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 and Private Options in the UK
NHS access to weight loss medication is provided through specialist tier 3 weight management services. Your GP can refer you if you meet the criteria. Eligibility typically requires 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. However, NHS availability varies significantly by region, and waiting lists can be lengthy in many areas.
Private prescription is available through GPhC-registered online pharmacies following an online clinical assessment. This route does not require an NHS referral and access is often faster, though you will pay privately. Costs typically range from £129–£320 per month depending on dose and medication. Check your BMI using our free BMI calculator to understand where you stand against NHS eligibility thresholds.
To explore whether prescription weight management medication suits your situation, start by having a conversation with your GP. They can assess your individual health profile, discuss how any medication might interact with a ketogenic or other dietary approach you're considering, and advise on NHS eligibility. You can also use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses — this may help guide your discussion. If you're not yet sure about your weight category, our free weight converter can help you understand your current weight across kg, stone, and lbs measurements relevant to NHS guidelines.
- 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 take GLP-1 medication while following a ketogenic diet?
Yes. GLP-1 medications like Mounjaro and Wegovy work independently of your dietary approach. However, always discuss your planned diet with your prescriber, as GLP-1 medications slow gastric emptying, which may interact with very low-carbohydrate eating. Your prescriber can advise on any adjustments needed and monitor your progress.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs ~15%), but individual responses vary. Both are once-weekly injections. Your prescriber will assess which is more suitable for you.
How do I know if I'm eligible for prescription weight loss treatment on the NHS?
You're typically eligible if you have a BMI of 30 or above, or 25–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea, cardiovascular disease). For South Asian, Chinese, Black African, or Black Caribbean adults, thresholds are lower. Your GP can assess your eligibility and refer you to a specialist tier 3 service.
Are there side effects I should know about with GLP-1 medications?
Common side effects include nausea, diarrhoea, vomiting, and constipation — typically mild and temporary as your body adjusts. Less common side effects include injection site reactions, fatigue, and dizziness. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or gallbladder issues. Your prescriber will discuss all risks with you.
Can I get GLP-1 medication privately without going through the NHS?
Yes. Private prescription through GPhC-registered online pharmacies is available following an online clinical assessment. You do not need an NHS referral. Access is typically faster than NHS routes, but you will pay privately. Costs range from approximately £129–£320 per month depending on dose and medication.
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.