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 Meal Replacements and Prescription Options in the UK
Weight loss meal replacements are convenient tools to reduce calorie intake, but many UK adults also have access to prescription weight management medication. If you're struggling with weight management, it's worth understanding both approaches — as well as how prescription options like Mounjaro and Wegovy work alongside lifestyle changes. This guide covers meal replacement options and explains how prescription weight loss medication fits into the UK health system. Use our free BMI calculator above to check where your current weight sits, and our GLP-1 weight loss calculator to explore what medication-supported weight loss might look like for you.
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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 Loss Medication
For many UK adults, prescription weight management is more effective than meal replacements alone. Three medications are currently licensed for weight management in the UK:
- Mounjaro (tirzepatide) — dual GIP and GLP-1 receptor agonist, once weekly, doses from 2.5–15 mg. In clinical trials, participants lost an average of 15–21% of body weight alongside reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — GLP-1 receptor agonist, once weekly, doses up to 2.4 mg. Clinical trials showed average weight loss of around 15% at the highest dose.
- Saxenda (liraglutide) — GLP-1 receptor agonist, daily injection, doses up to 3 mg.
All three are prescription-only and require a clinical assessment by a licensed prescriber to confirm eligibility. Individual results vary significantly, and these medications work best when combined with lifestyle changes.
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, Access, and Getting Started
In the UK, prescription weight loss medication is typically available to adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower eligibility thresholds (starting at BMI 27.5) apply for adults of South Asian, Chinese, Black African, or Black Caribbean heritage, as these groups face higher health risks at lower BMI levels.
You can access prescription weight loss medication through the NHS via specialist tier 3 weight management services (usually requiring a GP referral) or privately through UK-licensed online prescribers following an online clinical assessment. NHS access varies significantly by region and availability. Our weight converter and BMI calculator can help you understand where you currently sit against these thresholds — then speak with your GP about which option suits your 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.
Are weight loss meal replacements as effective as prescription medication?
Meal replacements can support weight loss by reducing overall calorie intake, but prescription medications like Mounjaro and Wegovy work on a physiological level to reduce appetite and food cravings. Clinical trials show higher average weight loss with prescription medication, though results vary. A combined approach — meal replacements plus prescription medication plus lifestyle changes — may be most effective. Your GP can advise what's right for you.
How do I know if I'm eligible for prescription weight loss medication in the UK?
You may be eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. South Asian, Chinese, Black African, or Black Caribbean adults may be eligible from a BMI of 27.5. Use the BMI calculator on this page to check your current BMI, then discuss eligibility with your GP.
Can I get prescription weight loss medication on the NHS?
Yes. Mounjaro and Wegovy are available on the NHS through specialist weight management services, but access varies significantly by region and waiting times can be lengthy. You'll typically need a GP referral to a tier 3 service. Private prescribing is also available through registered online prescribers without an NHS referral, though this involves a cost.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections, but Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Mounjaro may achieve slightly higher average weight loss in clinical trials (15–21% vs around 15% for Wegovy), but individual results vary significantly. Your prescriber will help choose which is most suitable.
Do prescription weight loss injections work without lifestyle changes?
These medications are most effective alongside a reduced-calorie diet and increased physical activity. They support appetite control and help you feel fuller, but they are not a substitute for lifestyle changes. Sustainable weight loss involves both medication (if prescribed) and behaviour change. Track your progress using our free progress tracker as you work toward your goals.
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.