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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A Weight Loss Diet: Combining Diet with Prescription Options in the UK
A weight loss diet works best when combined with the right support and, for some people, prescription medication. In the UK, adults struggling with excess weight have access to several evidence-based approaches: lifestyle changes, NHS support programmes, and prescription medications like Mounjaro and Wegovy. This guide covers sustainable diet strategies and explains how prescription weight management options fit into your overall plan. Whether you're managing your weight independently or considering medical support, understanding all your options helps you make informed decisions with your GP.
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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 Prescription Weight Loss Options: Mounjaro, Wegovy, and Saxenda
For eligible UK adults, prescription weight loss medications are available alongside diet and lifestyle changes. Three main options are licensed for weight management in the UK:
- Mounjaro (tirzepatide) — a once-weekly injection that activates dual GIP and GLP-1 pathways. In clinical trials, participants lost an average of 15–21% of body weight over 72 weeks alongside reduced-calorie diet and exercise.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Clinical trials showed average weight loss of approximately 15% of body weight at the maximum dose (2.4 mg).
- Saxenda (liraglutide) — a once-daily GLP-1 injection for those preferring daily dosing.
All are prescription-only medicines requiring clinical assessment. 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 significantly.
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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: How to Get Started
In the UK, prescription weight loss medication is available through two routes:
- NHS specialist services: Referral from your GP to a tier 3 or tier 4 weight management service. Availability varies by region, and waiting lists can be lengthy. Contact your GP to ask about specialist weight management services in your area.
- Private route: Online consultation with a UK-licensed prescriber, followed by prescription from a GPhC-registered pharmacy. Available without NHS referral, though costs apply (typically £129–£320+ per month depending on dose).
Regardless of route, prescription medications work best alongside a reduced-calorie diet, increased physical activity, and behaviour change support. Use our free GLP-1 weight loss calculator to explore potential weight loss projections at different doses. Your GP can advise which approach suits your circumstances best.
- 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 is the best weight loss diet?
The most effective weight loss diet is one you can sustain long-term. The NHS recommends aiming for 0.5–1 kg weight loss per week through a calorie deficit (typically 500 kcal/day). Mediterranean and low-carbohydrate diets have strong evidence for sustainability. For eligible adults, combining diet with prescription weight loss medication may improve results. Always consult your GP before starting any weight loss programme.
Are weight loss injections available on the NHS in the UK?
Yes, Mounjaro and Wegovy are available on the NHS through specialist weight management services (tier 3/4). Access requires referral from your GP and varies significantly by region — some areas have waiting lists of months. Private access is also available. Speak to your GP about which option is suitable for you.
How much weight can I expect to lose with prescription medication?
Clinical trials showed average weight loss of 15–21% of body weight with Mounjaro and approximately 15% with Wegovy, but individual results vary considerably. These medications work best alongside a reduced-calorie diet and increased physical activity. Your prescriber will monitor your progress and adjust your dose if needed.
What's the difference between a weight loss diet and weight loss medication?
A weight loss diet creates a calorie deficit through food and exercise alone. Prescription medications (like GLP-1 injections) work by reducing appetite, helping you feel fuller, and slowing digestion — they support, not replace, dietary changes. Most effective results combine both approaches with behaviour change support.
Who is eligible for prescription weight loss medication in the UK?
Typically, adults with a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions (diabetes, high blood pressure, cardiovascular disease). For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply. A prescriber will assess your individual eligibility during consultation.
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.