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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Intermittent Fasting for Weight Loss — UK Medication Guide
Intermittent fasting is a popular dietary approach that can help with weight management when combined with healthy eating habits. However, for adults struggling with weight loss, the NHS and private healthcare in the UK also offer prescription weight management options. This guide explains how intermittent fasting works, what UK-licensed weight loss medications are available, and how to find out if you're eligible for prescription support.
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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 Available
If intermittent fasting alone isn't delivering the results you need, prescription weight loss medications are available in the UK for eligible adults. Three medications are currently licensed for weight management:
- Mounjaro (tirzepatide) — a once-weekly injection that works as a dual GIP and GLP-1 receptor agonist, available through NHS specialist services or private prescribing
- Wegovy (semaglutide) — a once-weekly GLP-1 injection, licensed for weight loss in adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions
- Saxenda (liraglutide) — a once-daily GLP-1 injection, another option for weight management in the UK
In clinical trials, these medications helped participants achieve an average weight loss of 15–21% of body weight when used alongside dietary changes and increased physical activity. Your eligibility depends on your BMI and overall health profile, assessed by a healthcare professional.
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 — How to Access Weight Loss Support
NHS access: Weight loss medications are available through NHS tier 3 specialist weight management services, but availability varies significantly by region and waiting lists can be lengthy. Your GP can refer you to your local specialist service if you meet eligibility criteria.
Private access: You can access prescription weight loss medication through GPhC-registered online pharmacies following a clinical assessment — without a GP referral. This is often faster than NHS routes.
Whatever route you choose, weight loss medications work best alongside lifestyle changes — including diet, exercise, and behaviour modification. Our GLP-1 weight loss calculator can help you estimate potential results if you're considering medication options.
- 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 intermittent fasting alone help me lose weight without medication?
Yes, intermittent fasting can support weight loss when combined with a calorie deficit and healthy eating. The NHS recommends losing 0.5–1 kg per week through sustainable methods. However, some people find intermittent fasting challenging or insufficient, which is where prescription medications can help if you're eligible.
What BMI do I need to be eligible for prescription weight loss medication in the UK?
UK adults with a BMI of 30 or above are generally eligible. Those with a BMI of 27–29.9 may also qualify if you have weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Lower thresholds apply for people of South Asian, Chinese, Black African, or Black Caribbean heritage.
How long do I take Mounjaro or Wegovy?
Treatment duration varies. Some people use these medications for several months to achieve their weight loss goals, while others continue longer-term for weight maintenance. Your prescriber will discuss the appropriate duration with you based on your individual health needs and progress.
Will I regain weight after stopping intermittent fasting or weight loss medication?
Weight regain is possible if you return to previous eating patterns. The key to long-term weight management is sustainable lifestyle changes — regular physical activity, balanced nutrition, and healthy eating habits — whether or not you use medication.
How do I know if prescription weight loss medication is right for me?
A GP or licensed prescriber will assess your BMI, medical history, current medications, and weight loss goals. They'll discuss whether intermittent fasting, lifestyle support, or prescription medication is most appropriate for you. Use our BMI calculator to check your starting point, then speak with your healthcare provider.
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.