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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Meal Replacement Shakes and Prescription Weight Loss in the UK
Meal replacement shakes can be a useful part of weight management, but they work best alongside other strategies. If you're struggling to lose weight through diet alone, prescription weight management options are available in the UK for eligible adults. This guide explains how prescription weight loss medication compares to meal replacement approaches, and how to find out if you qualify for NHS support or private prescription options. Start by calculating your BMI using our free BMI calculator above to understand your current health status.
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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 Prescription Weight Loss Options
For adults in the UK, three prescription-only weight loss injections are licensed for weight management alongside diet and exercise:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, given once weekly. Clinical trials showed average weight loss of approximately 15–21% of body weight over 72 weeks when combined with a reduced-calorie diet and physical activity.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, given once weekly. Clinical evidence from the STEP trials demonstrated average weight loss of around 15% of body weight when used alongside lifestyle changes.
- Saxenda (liraglutide) — a GLP-1 receptor agonist, given as a daily injection. This option may be suitable for those who prefer daily dosing rather than weekly injections.
All three require a prescription from a UK-licensed prescriber and a clinical assessment to confirm eligibility. Individual results vary, and these medications are not suitable for everyone.
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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.
How to Access Weight Loss Treatment in the UK
You may be eligible for prescription weight loss medication 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 apply if you are of South Asian, Chinese, Black African, or Black Caribbean heritage.
NHS route: Ask your GP about referral to a specialist weight management service (tier 3). Waiting times vary by region, and not all areas have the same availability.
Private route: Access through a licensed online prescriber following a clinical consultation. This option does not require an NHS referral and is available without waiting lists.
Use our free GLP-1 weight loss calculator above to explore potential outcomes with prescription medication at different doses.
- 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 meal replacement shakes enough for weight loss?
Meal replacement shakes can support weight loss when part of a structured calorie deficit, but results are typically modest. They work best combined with other lifestyle changes. For some people, particularly those with a BMI of 30 or above, prescription weight loss medication alongside dietary support may be more effective and sustainable long-term.
What's the difference between meal replacements and weight loss injections?
Meal replacement shakes reduce calorie intake through portion control. Weight loss injections like Mounjaro and Wegovy work by suppressing appetite, slowing digestion, and altering how your body processes food signals — offering a different mechanism. Many people benefit from combining both approaches under professional guidance.
Am I eligible for prescription weight loss medication in the UK?
You may be eligible if your BMI is 30 or above, or 27–29.9 with a weight-related health condition like diabetes or high blood pressure. Adults of South Asian or Black African heritage may qualify at a lower BMI. Your GP or a licensed prescriber can assess your individual eligibility.
How much weight loss can I expect with prescription medication?
Clinical trials showed average weight loss of 15–21% of body weight with Mounjaro and around 15% with Wegovy over several months, alongside diet and exercise. However, individual results vary significantly. Some people lose more, some less — your prescriber will monitor your progress regularly.
Can I access prescription weight loss treatment through the NHS?
Yes, if your GP refers you to a specialist weight management service (tier 3), you may access these medications through the NHS. However, availability and waiting times vary greatly by region. Private online prescribing is also available in the UK without an NHS referral, typically with faster access but at a cost.
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.