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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Weight Loss Guide for UK Adults
If you're searching for weight loss information, you've come to the right place. Weight management in the UK involves understanding your starting point, exploring evidence-based approaches, and finding support that works for you. This guide covers prescription weight loss medication, NHS pathways, lifestyle strategies, and how to use tools like BMI calculators to track your progress. Whether you're looking at GLP-1 weight loss options or sustainable diet changes, we'll help you understand what's available and how to access it through the UK health system.
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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.
Weight Loss Options Available in the UK
The UK offers several evidence-based approaches to weight management. Lifestyle changes — including reduced calorie intake and increased physical activity — form the foundation of sustainable weight loss, with the NHS recommending a loss of 0.5–1 kg per week as safe and sustainable. Prescription weight loss medication is available through NHS specialist services or private prescribing for eligible adults. GLP-1 weight loss injections like Wegovy (semaglutide) and Mounjaro (tirzepatide) have shown clinical effectiveness, with participants in trials losing an average of 14–21% of body weight — though individual results vary significantly. NHS weight management services provide tier 1–4 support depending on your BMI and health needs. Use our free BMI calculator above to establish your starting point and explore which pathway may suit you. Access through your GP for NHS routes or through licensed private prescribers for faster access to prescription medication.
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.
Prescription Weight Loss Medication — What You Need to Know
Wegovy (semaglutide) is a once-weekly GLP-1 injection licensed for weight management in UK adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Clinical trials showed average weight loss of approximately 15% body weight at the maximum dose (2.4 mg), achieved alongside diet and exercise. Mounjaro (tirzepatide) is a dual GIP and GLP-1 injection, also once-weekly, with similar eligibility criteria and slightly higher average weight loss outcomes (15–21% in trials). Both are prescription-only medicines requiring clinical assessment. Side effects are common during the first weeks (nausea, diarrhoea) but often reduce over time. Neither medication is a replacement for lifestyle changes — they work most effectively combined with reduced-calorie diet and increased physical activity. Try our GLP-1 weight loss calculator to project potential results at different doses.
- 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.
What's the difference between weight loss medication and diet alone?
Prescription weight loss injections work alongside diet and exercise — they don't replace lifestyle changes. They help by reducing appetite and supporting you to eat less, making calorie reduction more manageable. Diet alone requires strict discipline; medication can reduce cravings, making adherence easier for some people. Individual results vary; some lose more weight with medication, others achieve similar results with diet alone.
How do I access weight loss medication on the NHS?
You'll need referral from your GP to a tier 3 specialist weight management service. Eligibility requires BMI of 30+ or BMI 27+ with weight-related conditions. Waiting times vary significantly by region — some areas have waits of 6+ months. If faster access is important, private online prescribing is available following clinical assessment with a UK-licensed prescriber.
Can I switch between Wegovy and Mounjaro?
Both are licensed for weight management with similar eligibility. Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist, while Wegovy (semaglutide) is GLP-1 only — slightly different mechanisms. A prescriber can advise switching if one isn't working well, though this requires clinical judgment. There's no simple dose-for-dose conversion chart.
What happens if I stop taking weight loss injections?
Weight regain is common after stopping — clinical evidence shows people typically regain weight over months if diet and exercise don't remain strict. This is why these medications are used as part of ongoing weight management, not a temporary fix. The benefits continue only while you're taking the injection alongside sustained lifestyle changes.
How do I know my weight loss is healthy and sustainable?
The NHS recommends losing no more than 0.5–1 kg (1–2 lbs) per week as safe and sustainable. Faster loss increases muscle loss risk. Track your progress using our free progress tracker to monitor weekly changes. If you're losing more than 1 kg weekly, discuss with your GP. A healthy BMI goal for most adults is 18.5–24.9 — use our BMI calculator to check your target range.
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.