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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One Week Weight Loss Diet: UK Prescription Options
A rapid one-week weight loss diet often focuses on extreme calorie restriction, but sustainable weight management in the UK increasingly involves prescription medication alongside lifestyle changes. If you're looking to lose weight effectively, understanding UK-licensed prescription options like Mounjaro and Wegovy—and whether you're eligible for NHS support—can help you achieve lasting results. This guide covers medication-based weight management available to UK adults, eligibility criteria, and how to start a conversation with your GP about prescription weight loss solutions.
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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
For adults looking for structured weight management in the UK, three prescription-only medications are licensed for weight loss: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections, whilst Saxenda is a daily injection.
- Mounjaro — A dual GIP and GLP-1 receptor agonist. Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks alongside reduced-calorie diet and increased physical activity. Starting dose 2.5 mg, maximum 15 mg weekly.
- Wegovy — A GLP-1 receptor agonist. Clinical trials showed average weight loss of approximately 15% of body weight. Starting dose 0.25 mg, maximum 2.4 mg weekly.
- Saxenda — A daily GLP-1 injection. Effective for weight management in eligible adults. Maximum dose 3 mg daily.
All require a prescription following clinical assessment. These medications work by reducing appetite, supporting fuller feelings, and slowing gastric emptying. Individual results vary significantly. Try our GLP-1 weight loss calculator to estimate potential weight loss 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.
NHS vs Private Access and Eligibility
NHS access to prescription weight loss medication is through specialist tier 3/4 weight management services, not routine GP prescribing. You must be referred by your GP, and availability varies significantly by region. Waiting lists can be lengthy in many areas.
Private access is available through GPhC-registered online pharmacies following an online clinical assessment—no NHS referral required.
Eligibility for either route: Adults with BMI 30 or above, or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, prediabetes, high blood pressure, sleep apnoea, cardiovascular disease history). For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds (27.5+) may apply. Speak to your GP to discuss which option suits you.
- 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.
Can I lose weight in one week with prescription medication?
Prescription weight loss medications like Mounjaro and Wegovy work over weeks and months, not days. Rapid one-week weight loss is not realistic or recommended. These medications support sustainable weight loss (typically 0.5–1 kg weekly) alongside diet and exercise. Results are individual.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), whilst Wegovy (semaglutide) activates one (GLP-1). Clinical trials showed Mounjaro users lost slightly more weight on average (15–21% vs ~15%). Both are once-weekly injections. Your prescriber will assess which is appropriate for you.
Am I eligible for NHS weight loss medication?
NHS eligibility typically requires BMI 30+, or BMI 27–29.9 with weight-related health conditions. You need a GP referral to a specialist weight management service. However, regional availability varies widely. Your GP can assess your individual circumstances and discuss options.
How do I start a conversation with my GP about weight loss medication?
Book an appointment and discuss your weight management goals. Bring your BMI (use our free BMI calculator above) and any weight-related health conditions. Your GP can assess eligibility for NHS specialist services or discuss private options. Be honest about your health and lifestyle.
Are weight loss injections safe?
Mounjaro, Wegovy, and Saxenda are licensed medicines with extensive clinical trial data. Common side effects include nausea and digestive changes, usually temporary. Serious side effects are rare. All require prescription and medical assessment to ensure suitability. Your prescriber will discuss risks and benefits.
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.