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 in the UK
Intermittent fasting is a popular eating pattern that alternates between periods of fasting and eating, and many people in the UK use it as part of their weight management strategy. While fasting schedules can support modest weight loss through calorie reduction, prescription weight management medication may offer additional support for eligible adults. This guide explores how intermittent fasting works alongside UK-licensed weight loss options like Mounjaro and Wegovy, helping you understand what's available through the NHS and privately.
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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 Medication Options
If you're considering intermittent fasting for weight management in the UK, prescription medication may complement your approach if you're eligible. Three medications are currently licensed for weight loss:
- Mounjaro (tirzepatide) — a once-weekly injection that activates GIP and GLP-1 pathways, helping reduce appetite and support feeling fuller after meals. Clinical trials showed participants lost an average of 15–21% of their body weight alongside lifestyle changes.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Trial data showed average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — a daily injection, an earlier GLP-1 option still available through NHS specialist services and privately.
Eligibility typically requires 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. Individual results vary, and these medications work most effectively when combined with reduced-calorie eating patterns and increased physical activity—similar to how intermittent fasting functions best with overall lifestyle support.
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 Access — Next Steps
NHS access: You can ask your GP about referral to a specialist tier 3 weight management service, where prescription weight loss medication may be considered. Waiting times and availability vary significantly by region (integrated care board). Many NHS services now offer tirzepatide as part of their weight management programmes.
Private access: These medications are also available through GPhC-registered online pharmacies following a consultation with a UK-licensed prescriber. This route doesn't require NHS referral and is often faster, though costs apply (typically £130–£320 monthly depending on dose).
Start by checking your BMI using our free BMI calculator above to understand where you sit on the NHS scale. Then speak with your GP about your weight loss goals—they can advise on local availability and whether prescription support might suit your situation alongside dietary approaches like intermittent fasting.
- 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.
Does intermittent fasting work better than medication for weight loss?
Both can be effective, but work differently. Intermittent fasting creates calorie restriction through eating windows; weight loss medications reduce appetite and support feeling fuller. Some people combine both approaches for better results. Individual response varies significantly. Clinical evidence supports prescription medication as effective for eligible adults, particularly those struggling with appetite control.
Will Mounjaro or Wegovy work if I'm doing intermittent fasting?
Yes. These medications complement fasting by reducing hunger during fasting windows and helping portion control during eating windows. They're designed to work alongside dietary changes and increased activity. Combining approaches may enhance results, but always discuss your intermittent fasting plan with the prescriber to ensure safety.
How do I know if I'm eligible for NHS weight loss medication?
NHS eligibility generally requires a BMI of 30 or above, or 27 or above with weight-related health conditions. Ask your GP about local tier 3 specialist weight management services. They can assess your individual circumstances and discuss what's available in your area. Waiting lists vary by region.
Can I get prescription weight loss medication privately without NHS referral?
Yes. Private online prescribing services offer access following an online clinical assessment with a UK-licensed prescriber. No NHS referral is needed. Costs apply, typically £130–£320 per month depending on dose and provider. Prescribers will still assess eligibility based on BMI and health conditions.
What's the difference between GLP-1 weight loss and just eating less with intermittent fasting?
Intermittent fasting relies on willpower to maintain eating windows; GLP-1 medications work on appetite hormones to naturally reduce hunger. This can make it easier to stick to calorie deficit without constant effort. Weight loss injections are prescribed when fasting or dietary changes alone haven't achieved results, or to enhance outcomes. Both work best alongside sustainable lifestyle changes.
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.