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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Weight Loss Countdown: UK Prescription Medication Options
If you're counting down to starting weight loss medication in the UK, understanding your prescription options is essential. Mounjaro, Wegovy, and Saxenda are all licensed for weight management in the UK and may help eligible adults lose weight alongside lifestyle changes. Whether you're considering NHS weight loss options or exploring private prescription weight loss in the UK, this guide explains what's available, who qualifies, and how to take the next step 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 Management Medications
Three prescription medications are currently licensed in the UK for weight management. Mounjaro (tirzepatide) is a once-weekly injection that works as a dual GIP and GLP-1 receptor agonist — helping regulate appetite and support feeling fuller after meals. Clinical trials showed participants lost an average of 15–21% of their body weight at maximum dose, though individual results vary. Wegovy (semaglutide) is also a once-weekly GLP-1 injection, with clinical evidence showing average weight loss of around 15% body weight. Saxenda (liraglutide) is a daily GLP-1 injection option.
To be eligible for prescription weight loss medication in the UK, you typically need 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 cardiovascular disease). Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may have access at lower BMI thresholds due to higher health risks at these weights. All three medications are prescription-only and require assessment by a qualified healthcare professional before being prescribed.
Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and our BMI calculator to check where you fall on the NHS weight categories.
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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.
NHS vs Private Access: Getting Started with Weight Loss Medication
NHS Access: Prescription weight loss medication through the NHS is available via specialist tier 3 weight management services. You'll typically need a referral from your GP, and access varies significantly by region. Waiting lists can be lengthy in many areas, sometimes stretching months or longer depending on your local integrated care board.
Private Access: Private prescription weight loss medication is available through UK-licensed online prescribers following a clinical assessment. This route does not require an NHS referral and offers faster access, though costs vary by dose and provider (typically £129–£320+ per month depending on medication and strength).
Next Steps: Start a conversation with your GP about nhs weight loss options and whether you're eligible. They can refer you to specialist services or discuss private options. Many people find that even discussing weight management with their GP leads to practical support and guidance tailored to their individual circumstances.
- 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's the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections licensed for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) works through GLP-1 alone. Clinical trials show both can support significant weight loss when combined with reduced-calorie diet and physical activity. Your prescriber will assess which is more suitable for your individual health profile.
How quickly can I start prescription weight loss medication?
NHS access depends on your local services and waiting lists—this can range from weeks to many months. Private prescription options are typically faster, often available within days of clinical assessment. Either route requires a prescription from a qualified healthcare professional following a clinical evaluation.
Am I eligible for weight loss medication on the NHS?
Generally, you're eligible if you have a BMI of 30 or above, or 27–29.9 with a weight-related health condition such as type 2 diabetes or high blood pressure. Your GP can assess your eligibility and refer you to specialist weight management services. Lower BMI thresholds may apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage.
Do weight loss injections work on their own?
No—prescription weight loss medications work best alongside a reduced-calorie diet and increased physical activity. They help regulate appetite and support feeling fuller, but sustainable weight loss requires lifestyle changes too. Your GP or prescriber will discuss how to combine medication with diet and exercise for best results.
Can I switch between Mounjaro and Wegovy?
Switching medications must always be managed by your prescriber. While both are GLP-1-based weight management options, they have different mechanisms and dosing schedules. Your prescriber will assess whether a switch is appropriate and how to do it safely based on your individual response and health needs.
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.