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
What Is Weight Loss Diet? UK Guide to Medication and Lifestyle
A weight loss diet is a structured eating plan designed to create a calorie deficit, helping you lose weight alongside physical activity and lifestyle changes. In the UK, weight management combines dietary approaches with evidence-based support—ranging from self-help strategies to prescription medications like Mounjaro and Wegovy for eligible adults. Understanding your options helps you choose an approach suited to your health needs and circumstances. This guide covers diets, NHS weight loss support, and how prescription weight loss medication fits into the bigger picture of weight management in the UK.
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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-Licensed Prescription Weight Loss Options
For adults struggling with weight management, the UK offers several prescription-only options alongside dietary changes. Mounjaro (tirzepatide) is a once-weekly injection that works as a dual GIP and GLP-1 receptor agonist, helping regulate appetite and food cravings. Wegovy (semaglutide) is another once-weekly GLP-1 injection licensed for weight management. Both require a prescription following clinical assessment.
Clinical trial evidence shows that on average, Mounjaro users lost approximately 15–21% of their body weight over 72 weeks, whilst Wegovy users lost around 15% over 68 weeks—though individual results vary significantly. These medications are prescribed for adults with a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or heart disease. Access is available through NHS specialist weight management services or private prescribing following online clinical assessment. Calculate your personal BMI instantly using our free BMI calculator to see whether you might be eligible for prescription 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 Weight Loss vs Private Access in the UK
The NHS provides weight loss support through a tiered system. Tier 1 includes self-help tools and community programmes; Tier 2 offers primary care-based behaviour change support; Tier 3 comprises specialist multidisciplinary weight management services where prescription medications may be considered. Referral to NHS specialist services typically comes from your GP, though waiting lists vary significantly by region.
Private access to weight loss medication is also available in the UK through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. This route doesn't require NHS referral and can be faster. Whichever route you choose, prescription medications work best alongside a reduced-calorie diet and increased physical activity. Speak to your GP to discuss which approach suits your circumstances, or use our free GLP-1 weight loss calculator to explore potential outcomes with medication support alongside lifestyle changes.
- 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 a weight loss diet and weight loss medication?
A weight loss diet is a structured eating plan creating a calorie deficit through reduced food intake. Prescription weight loss medication like Mounjaro or Wegovy works by reducing appetite and cravings, making it easier to stick to a lower-calorie diet. Medications are typically used alongside dietary and lifestyle changes, not instead of them.
Am I eligible for prescription weight loss medication on the NHS?
NHS prescription weight loss medication is typically available through specialist weight management services for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Regional availability varies. Ask your GP for a referral to your local tier 3 weight management service to find out if you're eligible in your area.
How much weight can I expect to lose with Mounjaro or Wegovy?
Clinical trials showed average weight loss of 15–21% body weight with Mounjaro and around 15% with Wegovy over the trial period. However, individual results vary significantly based on your starting weight, diet, activity level, and how your body responds. Use our free GLP-1 weight loss calculator to explore potential ranges based on your circumstances.
What's the best weight loss diet for me?
The best diet is one you can sustain. Evidence supports calorie deficit diets (aiming for 0.5–1 kg per week loss), Mediterranean-style eating, and intermittent fasting for some people. Your GP or a dietitian can advise on approaches suited to your health conditions and preferences. Our free BMI calculator and progress tracker can help you monitor your results.
Can I get weight loss medication privately if the NHS waiting list is too long?
Yes. Private access to prescription weight loss medication is available through UK-registered online pharmacies following an online clinical assessment. This can be faster than NHS referral, though costs vary by dose and provider. Always ensure any private provider is GPhC-registered and the prescriber is UK-licensed.
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.