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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Twenty Pound Weight Loss: UK Prescription Medication Options
Losing twenty pounds (approximately 9 kg) is an achievable weight loss goal that can significantly improve your health. In the UK, several prescription weight management options are available to eligible adults alongside diet and exercise. These medications work by reducing appetite and supporting sustainable weight loss. Understanding which options might suit you, how to access them, and what to expect is essential before starting any weight loss programme. This guide covers prescription weight loss medication available in the UK and how to determine if you're eligible.
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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), Wegovy (semaglutide), and Saxenda (liraglutide). All three are GLP-1 receptor agonists (Mounjaro is a dual GIP/GLP-1 agonist) that work by reducing appetite and helping you feel fuller after eating.
In clinical trials, these medications supported average weight loss of 14–21% of body weight over several months when combined with a reduced-calorie diet and increased physical activity. For someone starting at a heavier weight, this could easily exceed 20 pounds of weight loss. However, individual results vary significantly—some people lose more, some less. All three are prescription-only medicines and require a clinical assessment before being prescribed. You cannot simply request them from a GP; you must be assessed for eligibility based on your BMI and health status.
To understand if you might be eligible, calculate your BMI using our free BMI calculator above, which shows where you sit against NHS guidelines and typical eligibility thresholds.
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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, Access, and Next Steps
In the UK, you're typically eligible for prescription weight loss medication if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). People of South Asian, Chinese, Black African, or Black Caribbean heritage may have slightly lower eligibility thresholds due to higher health risks at lower BMIs.
You can access weight loss medication through the NHS via referral to a specialist weight management service, though waiting times and regional availability vary significantly. Alternatively, prescription weight loss medication is available through private online prescribing following an online clinical assessment. Either route requires a licensed prescriber to confirm you're suitable. Your first step is to speak with your GP or explore private prescribing options. Track your progress using our free progress tracker as you work towards your twenty-pound weight loss goal.
- 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.
How much weight could I realistically lose with prescription medication?
In clinical trials, prescription weight loss medications supported average losses of 14–21% of body weight over 68–72 weeks alongside diet and exercise. For someone starting at a higher weight, this could equate to well over twenty pounds. However, results vary between individuals—some lose more, some less. These medications work best when combined with lifestyle changes, not as replacements for them.
How do I know if I'm eligible for weight loss medication on the NHS?
Your GP can assess your eligibility based on your BMI and health history. Generally, you need a BMI of 30 or above, or 27–29.9 with a weight-related health condition. Specialist tier 3 weight management services then decide whether to prescribe. Regional availability varies, so ask your GP about local services and waiting times.
What's the difference between NHS and private weight loss medication?
NHS access involves referral to a specialist service (often with waiting lists) and is free at the point of use. Private prescribing is faster—available through online assessment—but costs £130–£320 monthly depending on dose. Both require a licensed prescriber and clinical assessment; both require lifestyle changes alongside medication.
Are weight loss injections the same as insulin?
No. Prescription weight loss medications like Mounjaro and Wegovy are GLP-1 receptor agonists, not insulin. They work by mimicking a natural hormone that regulates appetite and blood sugar. They're injected once weekly (or daily for Saxenda) and are used specifically for weight management in eligible adults.
How can I track my progress towards twenty pounds of weight loss?
Use our free progress tracker on this site to log your weight weekly and visualise your journey towards your goal. Consistent tracking helps you stay motivated and identify patterns. Also use our free weight converter to switch between kg, stone, and pounds as you track—UK measurements make it personal and relevant.
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.