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
Free tracker included with every download this week
1 Meal a Day for Weight Loss — UK Prescription Options
Eating just one meal a day is an extreme approach to weight loss that many people try, but it can be difficult to sustain and may not be the most effective method for long-term weight management in the UK. For adults struggling with their weight, prescription medications available through the NHS or private prescribing offer evidence-based alternatives. Understanding your BMI, eligibility for weight management options, and having a conversation with your GP can help you find a sustainable approach that works for you.
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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 Prescription Weight Loss Options
For adults with a BMI of 30 or above, or 27 or above with weight-related health conditions, prescription weight management medications are available in the UK. The three main options are Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections; Saxenda is a daily injection.
Clinical trials show these medications may help achieve weight loss when combined with reduced-calorie eating and increased physical activity. In SURMOUNT trials, Mounjaro helped participants lose an average of 15–21% of their body weight. Wegovy showed similar results in STEP trials. Individual results vary significantly, and these medications work alongside lifestyle changes, not instead of them. All are prescription-only and require assessment by a licensed prescriber to determine suitability.
Check your eligibility using our free BMI calculator — knowing your starting BMI is the first step toward understanding what options may be available to you.
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 and Next Steps
In the UK, prescription weight loss medication is available through two routes. NHS access is via referral to tier 3 specialist weight management services — your GP can discuss referral, though waiting lists vary significantly by region. Private access is through online prescribing services where a UK-licensed prescriber assesses eligibility following an online consultation.
Rather than attempting extreme dietary restrictions like one meal a day, speaking with your GP about structured weight management support is recommended. Your GP can assess your health, discuss your goals, and advise whether prescription medication, NHS services, or lifestyle-focused approaches are most appropriate for you. Our free GLP-1 weight loss calculator and progress tracker can help you monitor progress alongside any approach you choose.
- 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.
Is one meal a day a safe way to lose weight?
Eating one meal daily is very restrictive and can lead to nutrient deficiencies, muscle loss, and fatigue. The NHS recommends sustainable weight loss of 0.5–1 kg per week through balanced eating and activity. For rapid or significant weight loss, prescription medications combined with professional support offer safer, evidence-based alternatives.
What is the difference between Mounjaro and Wegovy for weight loss?
Both are prescription-only injections used for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with a maximum dose of 15 mg weekly. Wegovy (semaglutide) is a GLP-1 agonist with a maximum dose of 2.4 mg weekly. Clinical trial results are similar, but individual response varies. Your prescriber will advise which is most suitable.
How do I know if I'm eligible for prescription weight loss medication in the UK?
You may be eligible if your BMI is 30 or above, or 27 or above with a weight-related condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). Use our free BMI calculator to check your starting point, then discuss with your GP or a licensed prescriber about eligibility and options.
Can I get prescription weight loss medication through the NHS?
Yes. Specialist NHS weight management services (tier 3) can prescribe medications including Mounjaro and Wegovy. Access is via GP referral, and availability varies by region. Waiting lists can be lengthy. Private online prescribing offers faster access if you meet clinical criteria.
Will prescription weight loss medication work without lifestyle changes?
No. Prescription medications are most effective alongside a reduced-calorie diet and increased physical activity. Clinical trials all combined medication with lifestyle support. Medication may help reduce appetite and cravings, making dietary changes easier to manage, but it is not a substitute for eating well and moving more.
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.