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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Forty Pound Weight Loss: UK Prescription Medication Options
Losing forty pounds (approximately 18kg) is an achievable goal with the right support, and prescription weight management options are now available in the UK. If you're eligible, medications like Mounjaro and Wegovy can support significant weight loss alongside lifestyle changes. This guide explains UK-licensed options, who qualifies, and how to access treatment through the NHS or private prescribing. Start by calculating your BMI using our free BMI calculator to understand where you stand against NHS guidelines.
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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 Weight Loss Medications
Three prescription medications are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist. In clinical trials, participants lost an average of 15–21% of their body weight over 72 weeks, meaning a 200-pound person might lose around 30–42 pounds. Doses range from 2.5mg to 15mg, injected once weekly.
- Wegovy (semaglutide) — A GLP-1 receptor agonist injected once weekly. Clinical trials showed an average weight loss of around 15% body weight, potentially 30 pounds for a 200-pound person. Maximum dose is 2.4mg.
- Saxenda (liraglutide) — A daily GLP-1 injection with similar efficacy to Wegovy. All three medications work by reducing appetite and helping you feel fuller after smaller meals.
Individual results vary significantly. These medications are prescribed alongside a reduced-calorie diet and increased physical activity—they're not replacements for lifestyle changes. Use our GLP-1 weight loss calculator to explore 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.
NHS Eligibility and How to Access Treatment
To qualify for prescription weight loss medication in the UK, you generally need a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Lower thresholds apply if you're of South Asian, Chinese, Black African, or Caribbean heritage due to higher metabolic health risks at lower BMIs.
NHS route: Ask your GP for a referral to a tier 3 specialist weight management service. Availability and waiting times vary significantly by region—some areas have lengthy waiting lists.
Private route: Access through an online clinical assessment with a UK-licensed prescriber, usually quicker than NHS referral. Costs typically range from £129–£320 per month depending on dose and provider.
Either way, a qualified healthcare professional will assess your suitability. Start by discussing weight management options with your GP.
- 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.
Will I lose forty pounds with prescription weight loss medication?
Results vary individually based on starting weight, dose, and lifestyle adherence. Clinical trials show average weight losses of 15–21% body weight—for a 200-pound person, that's roughly 30–42 pounds over 72 weeks. However, some people lose more, some less. Medication works best combined with a reduced-calorie diet and physical activity, not as a substitute for lifestyle changes.
Am I eligible for Mounjaro or Wegovy on the NHS?
You may be eligible if your BMI is 30 or above, or 27–29.9 with weight-related health conditions (diabetes, hypertension, etc.). Eligibility thresholds are lower for people of South Asian, Chinese, Black African, or Caribbean heritage. Ask your GP for referral to a specialist weight management service to be assessed formally.
How long does it take to lose forty pounds with these medications?
Based on clinical trial data, a forty-pound weight loss might take 4–6 months on maintenance doses, though timelines vary. Doses are gradually escalated over the first 16–20 weeks, so initial losses may be slower. Consistent adherence to the injection schedule, diet, and activity recommendations speeds results.
What's the difference between NHS and private prescription routes?
NHS access requires a GP referral to a tier 3 specialist service and may involve waiting lists (varies by region). Private access is through online clinical assessment with a UK-licensed prescriber—usually faster, but you pay out of pocket (typically £129–£320 monthly). Both require a valid prescription and clinical suitability assessment.
Can I switch between Mounjaro and Wegovy if one doesn't work for me?
Yes, but any switch must be managed by your prescriber. Mounjaro (dual GIP/GLP-1) and Wegovy (GLP-1-only) work differently, so your prescriber will advise on the best approach. Never self-switch medications. Discuss alternative options with your GP or private prescriber if you experience side effects or plateaued weight loss.
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.