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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Fast Weight Loss Diet Schedule — UK Medication Options
A diet schedule for weight loss fast works best when combined with the right support, which for many UK adults may include prescription weight management medication. Losing weight quickly without medical support can be unsustainable and risky, but evidence-based approaches using both lifestyle changes and, where appropriate, prescription options like GLP-1 injections can help eligible adults achieve meaningful results. The NHS recognises that weight management is complex, and prescription medications are now available for those who qualify. This guide explores how diet schedules work alongside weight management options available in the 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 Management Options
Three main prescription weight loss medications are licensed in the UK for weight management, and they work best alongside a reduced-calorie diet schedule:
- Mounjaro (tirzepatide) — dual GIP and GLP-1 receptor agonist, once-weekly injection, doses 2.5–15 mg. Clinical trials showed average weight loss of approximately 15–21% of body weight.
- Wegovy (semaglutide) — GLP-1 receptor agonist, once-weekly injection, doses 0.25–2.4 mg. Clinical evidence demonstrates average weight loss of around 14.9% of body weight.
- Saxenda (liraglutide) — GLP-1 receptor agonist, once-daily injection, doses 0.6–3 mg.
All three are prescription-only medicines. Adults with a BMI of 30 or above, or 27 or above with weight-related health conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea), may be eligible. Individual results vary significantly, and medications are used alongside dietary changes and increased physical activity, not instead of them. Our GLP-1 weight loss calculator can help you understand potential outcomes at different doses.
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.
Getting Started: NHS vs Private Access in the UK
NHS access to prescription weight management typically flows through tier 3 specialist weight management services, accessed via GP referral. Waiting lists vary significantly by region and can be lengthy. Private access is available through UK-licensed online prescribers following a clinical assessment, without NHS referral, though costs apply (typically £129–£320+ per month depending on dose and provider).
Before pursuing any prescription option, speak with your GP about your weight loss goals and whether you're a suitable candidate. A prescriber will assess your BMI, health history, and any weight-related conditions. Calculate your personal BMI using our free BMI calculator to understand your starting point, and use our progress tracker to monitor your weight journey once you've begun any treatment plan.
- 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.
How quickly can I lose weight with prescription weight management medication?
Clinical trials show average weight loss of 15–21% of body weight over 68–72 weeks, but results vary widely between individuals. The NHS recommends a sustainable rate of 0.5–1 kg per week. Prescription medications work alongside diet and exercise, not instead of them, and are typically titrated gradually (starting at lower doses and increasing every 4 weeks).
What diet schedule works best with weight loss medication?
A reduced-calorie diet creating a deficit of around 500 kcal per day typically supports approximately 0.5 kg weight loss per week. GLP-1 medications reduce appetite, making calorie reduction easier. Focus on whole foods, protein, vegetables, and avoid highly processed foods. Your prescriber or a dietitian can provide personalised guidance alongside medication.
Are weight loss injections available on the NHS in the UK?
Yes, prescription weight loss medications (Mounjaro, Wegovy, and Saxenda) are available through NHS tier 3 specialist weight management services, but access depends on your local NHS area (ICB) and referral criteria. GPs can refer eligible patients, though waiting lists vary significantly. Private access is also available through UK-licensed online prescribers.
How is my BMI used to determine weight loss medication eligibility?
Adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions, may be eligible for prescription weight management. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, NHS guidelines recommend lower thresholds (27.5 or above). A prescriber will assess your individual circumstances — use our BMI calculator to check yours.
Can I lose weight fast with diet alone, without medication?
Yes, diet changes alone can produce weight loss, but rapid loss without medical support risks muscle loss and nutritional deficiency. The NHS recommends 0.5–1 kg per week as sustainable. If you've struggled with diet-only approaches, prescription weight management medication may be worth discussing with your GP, as it's designed to support those for whom lifestyle changes alone haven't been sufficient.
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.