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
Eight Week Weight Loss in the UK: Prescription Medication Options
An eight-week timeframe for weight loss is realistic with the right support. In the UK, prescription weight management medications like Mounjaro and Wegovy can be part of a comprehensive approach to losing weight, alongside diet and exercise. This guide explains what's available, who is eligible, and how to access prescription weight loss medication through the NHS or privately.
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 prescription medications are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — a once-weekly dual GIP and GLP-1 receptor agonist injection. Clinical trials showed participants lost an average of 15–21% of body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a once-weekly GLP-1 receptor agonist injection. Evidence suggests an average weight loss of around 15% body weight over similar timeframes.
- Saxenda (liraglutide) — a once-daily GLP-1 injection, available for several years, with average weight loss around 5–10% of body weight.
All three are prescription-only and require a clinical assessment before being prescribed. Results vary between individuals. These medications are typically used alongside lifestyle changes, not instead of them. Our free GLP-1 weight loss calculator can help you estimate 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.
Eligibility and How to Get Weight Loss Medication in the UK
You may be eligible for prescription weight loss medication in the UK if you have a BMI of 30 or above, or a BMI of 27–29.9 with a weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. Lower BMI thresholds may apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage.
To access medication:
- NHS route: Discuss weight management with your GP, who can refer you to a specialist weight management service. Availability varies by region and waiting times can be lengthy.
- Private route: Prescription weight loss medication is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. This is faster but involves a cost.
Use our free BMI calculator to check your current BMI and understand your eligibility starting point. Your GP remains the best source of personalised advice.
- 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 a significant amount of weight in eight weeks?
Individual results vary significantly. An eight-week window is relatively short, but with prescription medication alongside a reduced-calorie diet and increased physical activity, many people see noticeable progress. Clinical trials show average weight loss over 8–12 weeks is typically 5–10 lbs (2–4 kg). Your prescriber can give you realistic expectations based on your individual situation.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections for weight management. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist — it activates two hormone pathways. Wegovy (semaglutide) activates GLP-1 only. Clinical trial data suggests Mounjaro may result in slightly higher average weight loss, but individual results vary. Your prescriber will assess which is more suitable for you.
Is weight loss medication available on the NHS?
Yes, but through specialist tier 3 weight management services, not standard GP prescription. You'll need to be referred by your GP, and availability varies significantly by region. Waiting lists can be months to years in some areas. Private prescription weight loss medication is available faster but involves a cost, typically £129–£320 per month depending on dose and provider.
What side effects should I expect from weight loss injections?
Most common side effects include nausea, diarrhoea, constipation, and reduced appetite — particularly in the first few weeks as your body adjusts. These often improve over time. Serious side effects are rare but can include gallbladder problems or severe stomach pain. Your prescriber will discuss all potential risks and monitor you throughout treatment.
Do I need to diet and exercise alongside weight loss medication?
Yes. Prescription weight loss medications like Mounjaro and Wegovy work best alongside a reduced-calorie diet and increased physical activity. Clinical trial participants all combined medication with lifestyle changes. Medication supports weight loss but is not a standalone solution. Your GP or weight management service can advise on dietary approaches suited to you.
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.