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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Four Week Weight Loss Plan With Prescription Medication
A structured four week weight loss plan in the UK can include prescription medications alongside dietary changes and physical activity. If you have a BMI of 30 or above, or 25 to 29.9 with weight-related health conditions, you may be eligible for prescription weight management options like Mounjaro or Wegovy. These are GLP-1 medications licensed in the UK that work alongside lifestyle changes to support sustainable weight loss. Calculate your BMI using our free BMI calculator above to check where you stand, then discuss prescription options with your GP.
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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 Loss Options
Three prescription weight loss medications are currently licensed in the UK for weight management: Mounjaro (tirzepatide), a dual GIP and GLP-1 receptor agonist given as a once-weekly injection; Wegovy (semaglutide), a GLP-1 receptor agonist also injected once weekly; and Saxenda (liraglutide), a daily GLP-1 injection. Clinical trials show that Mounjaro may help participants lose an average of 15–21% of their body weight, whilst Wegovy supports approximately 15% average weight loss — though individual results vary significantly. Both are prescription-only medicines requiring a clinical assessment before use. A four week weight loss plan involving prescription medication works most effectively when combined with a reduced-calorie diet and increased physical activity. Your prescriber will assess your BMI weight loss potential and overall health to determine which medication, if any, suits your circumstances.
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 Getting Started
In the UK, you can access prescription weight loss medication through the NHS weight loss pathway or privately. NHS access is through tier 3 specialist weight management services, typically following a GP referral — though availability and waiting times vary significantly by region. Private access is available through UK-licensed prescribers following an online consultation without NHS referral, though costs apply. To begin a four week weight loss plan, speak with your GP about prescription weight loss uk options, or explore private prescribing if you prefer faster access. Your eligibility depends on your BMI, age, health conditions, and ethnicity — lower BMI thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses and support your conversation with a healthcare professional.
- 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 NHS four week weight loss plan with medication?
The NHS does not have a standardised "four week" plan. Instead, weight loss through NHS services is gradual and sustained. Prescription medications like Mounjaro or Wegovy are initiated at lower doses and increased over weeks, with dietary and lifestyle support ongoing. Your GP or specialist will create a personalised plan based on your health and goals.
How much weight can I lose in four weeks with Mounjaro or Wegovy?
Clinical trials show gradual weight loss over 16+ weeks. In the first four weeks, you may lose 2–5 kg depending on dose, starting weight, and adherence to diet and exercise. Individual results vary significantly. Never expect rapid loss — sustainable weight loss of 0.5–1 kg per week is considered healthy by NHS standards.
Am I eligible for prescription weight loss medication on the NHS?
You may be eligible if your BMI is 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Lower thresholds (BMI 27.5+) apply for South Asian and Black African heritage adults. Ask your GP about referral to a tier 3 weight management service in your area.
What is the difference between Mounjaro and Wegovy for weight loss?
Mounjaro is a dual GIP and GLP-1 agonist, typically producing slightly higher average weight loss (15–21%) than Wegovy (approximately 15%). Both are once-weekly injections. Mounjaro starts at 2.5 mg rising to 15 mg; Wegovy starts at 0.25 mg rising to 2.4 mg. Your prescriber will advise which is more suitable for you.
Can I get a four week weight loss plan prescription without seeing my GP?
Private UK-licensed prescribers offer online consultations and can issue prescriptions without NHS referral, providing faster access than NHS routes. However, you must still have a clinical assessment — prescribers cannot issue medication without evaluating your health, BMI, and medical history. This protects your safety.
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.