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
1 Week Weight Loss in the UK: Medication Options Explained
Losing weight in just one week isn't realistic for most people — and gradual weight management can be unhealthy. However, if you're looking for effective weight management support in the UK, prescription medications are available alongside lifestyle changes. This guide explains prescription weight loss options, who's eligible, and how NHS and private routes work. Use our free BMI calculator above to understand your starting point, and our GLP-1 weight loss calculator to explore realistic projections with medication support.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Medications
Three medications are licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These are prescription-only medicines that work by reducing appetite and helping you feel fuller after eating. Clinical trials show that combined with a reduced-calorie diet and increased activity, these medications help with sustained weight loss — not rapid one-week drops.
- Mounjaro: Once-weekly injection; dual GIP and GLP-1 agonist; clinical trials showed average weight loss of 15–21% over 72 weeks
- Wegovy: Once-weekly GLP-1 injection; average weight loss of around 15% in clinical trials at the maximum dose
- Saxenda: Daily GLP-1 injection; approved for weight management but less commonly prescribed than Mounjaro or Wegovy in the UK
All three work best when used alongside healthy eating and exercise. Individual results vary significantly. A prescriber will assess whether medication is suitable for you based on your individual health profile.
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 Eligibility and How to Access Prescription Weight Loss
To be eligible for prescription weight loss medication in the UK, you typically need a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Lower thresholds (from BMI 27.5) apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage.
NHS route: Ask your GP for a referral to a specialist tier 3 weight management service. Availability and waiting times vary significantly by region.
Private route: Prescription medications are available through GPhC-registered online prescribing services following a clinical assessment — no NHS referral needed.
Either way, a licensed prescriber will assess your eligibility. Use our BMI calculator to check your starting point before your consultation.
- 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 safely?
Losing 1–2 lbs (0.5–1 kg) per week is considered safe and sustainable according to NHS guidelines. Faster weight loss risks losing muscle and can be unsustainable. Prescription medications support gradual, consistent weight loss over weeks and months, not rapid drops in a single week.
Do I need to be on a diet to use weight loss medication?
Yes. Prescription weight loss medications work best alongside a reduced-calorie diet and increased physical activity. Medication alone isn't effective. Your prescriber or a weight management programme will provide dietary guidance. Think of medication as a tool that supports your lifestyle changes, not a replacement for them.
How long does it take to see results with Mounjaro or Wegovy?
Most people notice changes in appetite within 1–2 weeks, but measurable weight loss typically takes 4–8 weeks. Clinical trials show significant results after 12–16 weeks. Weight loss is gradual and sustainable — you're aiming for 0.5–1 kg per week, which adds up to 2–4 kg (4–9 lbs) per month on average.
Can my GP prescribe weight loss injections, or do I need a specialist?
Currently in the UK, prescription weight loss medications are typically prescribed by specialist tier 3 weight management services on the NHS, or through private online prescribers. Some GPs may prescribe in future as guidance evolves, but availability is currently limited. Ask your GP about referral options in your area.
What's the difference between NHS and private weight loss medication access?
NHS access requires a GP referral to specialist services and can involve waiting lists of weeks to months. Private access is available through online prescribers following a clinical assessment, with faster turnaround but at personal cost. Both routes require a prescription from a licensed prescriber and a clinical assessment of your eligibility.
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.