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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NHS Weight Loss Apps and Prescription Medication in the UK
NHS weight loss apps can be helpful tools for tracking progress, but they work best alongside professional support. For adults struggling with weight management in the UK, prescription options are now available. This guide explores how NHS weight loss initiatives compare with prescription medication, who is eligible, and how to access support through your GP. Whether you're looking for digital tools or medical intervention, understanding your options is the first step toward sustainable weight loss UK.
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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
If you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions, you may be eligible for prescription weight loss medication. The UK has three licensed options:
- Mounjaro (tirzepatide) — a once-weekly GLP-1 injection, maximum dose 15 mg. Clinical trials showed average weight loss of 15–21% of body weight.
- Wegovy (semaglutide) — a once-weekly GLP-1 weight loss injection, maximum dose 2.4 mg. Average weight loss in trials was approximately 15% of body weight.
- Saxenda (liraglutide) — a daily injection, maximum dose 3 mg. Older option with slightly lower average weight loss outcomes.
All three are prescription-only medicines requiring a clinical assessment. Individual results vary, and these work best alongside dietary changes and increased physical activity. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses, and our BMI calculator to check your personal eligibility threshold.
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.
Accessing Weight Loss Support: NHS vs Private
NHS route: You can ask your GP for a referral to your local tier 3 specialist weight management service. Waiting times vary significantly by region, and availability is not uniform across England. Some areas have longer waits than others. NHS services focus on behaviour change, dietetics, and physical activity support, with prescription medication available through specialist clinicians.
Private route: GPhC-registered online pharmacies offer prescription weight loss medication following an online clinical assessment with a UK-licensed prescriber. This bypasses NHS waiting lists but involves upfront costs (typically £129–£320 monthly depending on dose). Both pathways require a prescription and clinical judgment about suitability. Speak to your GP about which approach is right for you. Track your progress with our free progress tracker once you begin any weight loss programme.
- 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.
Are NHS weight loss apps effective on their own?
NHS apps like the Weight Loss Plan can help with tracking and motivation, but research shows they work best alongside professional support—either through a GP-guided programme or specialist weight management service. Apps alone are unlikely to deliver sustainable weight loss without behaviour change support.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections, but Mounjaro uses a dual GIP+GLP-1 mechanism (maximum 15 mg) whilst Wegovy is GLP-1 only (maximum 2.4 mg). Clinical trials suggest Mounjaro may produce slightly higher average weight loss, but individual results vary significantly. A prescriber will recommend the most suitable option for you.
How do I know if I'm eligible for prescription weight loss medication?
You're potentially eligible if your BMI is 30 or above, or 27–29.9 with a weight-related condition (diabetes, high blood pressure, sleep apnoea). For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds apply. Use our BMI calculator to check your personal status, then discuss eligibility with your GP.
How long does it take to lose weight on GLP-1 medication?
Weight loss begins within the first few weeks for most people, but the full effect typically emerges over 3–6 months as doses are increased. The NHS recommends gradual weight loss of 0.5–1 kg per week for sustainable results. Our weight loss calculator can help you understand realistic timelines.
Can I switch from one weight loss injection to another?
Yes, it's possible to switch between Mounjaro, Wegovy, and Saxenda, but this must always be managed by your prescriber. There is no official conversion chart—switching requires individual clinical assessment. Never attempt to switch medications without guidance from the prescriber managing your care.
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.