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 Replacement and Prescription Medication in the UK
While meal replacement shakes can support weight management, prescription weight loss medications offer a different approach for eligible UK adults. If you're considering weight management options, it's worth understanding both dietary methods and prescription treatments available through the NHS or private prescribers. This guide explains how prescription weight loss medications work, who can access them, and how they compare to traditional meal replacement strategies.
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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 who meet eligibility criteria, three prescription medications are licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These work differently from meal replacement products — they are injectable GLP-1 receptor agonists (or in Mounjaro's case, a dual GIP/GLP-1 agonist) that help regulate appetite and support feeling fuller after meals.
Clinical evidence shows that prescription weight loss medication, when used alongside a reduced-calorie diet and increased physical activity, can support meaningful weight loss. In trials, Mounjaro helped participants lose an average of 15–21% of their body weight, while Wegovy showed average losses of around 15%. Individual results vary significantly. These medications are prescribed through specialist NHS services or following a clinical assessment with a private UK-licensed prescriber — they are not available over-the-counter.
Use our free GLP-1 weight loss calculator to explore potential weight loss projections at different doses, and our BMI calculator to check if you fall within 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.
NHS Access vs Private Prescribing — How to Find Out If You're Eligible
In the UK, prescription weight loss medication is available through two routes. NHS access: Specialist tier 3 weight management services assess eligibility and may prescribe Mounjaro or Wegovy. You'll need a GP referral and typical eligibility includes a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. Waiting times for NHS specialist services vary widely by region — some areas have significant waiting lists.
Private access: Available through GPhC-registered online prescribing services following a clinical assessment. No NHS referral needed, and prescription weight loss medication can be accessed more quickly. Costs typically range from £129–£320 per month depending on dose and provider.
Start by speaking with your GP about which route suits your circumstances. They can assess your health and either refer you to NHS specialist services or advise on private options. Combined with structured meal planning and lifestyle changes, prescription medication may support sustained weight management.
- 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 do prescription weight loss medications differ from meal replacement shakes?
Meal replacements reduce calories by substituting meals with lower-calorie alternatives. Prescription medications like Mounjaro and Wegovy work via hormone pathways to reduce appetite and help you feel fuller. Both can support weight loss, but medications offer a different mechanism. Many people use both approaches together — meal replacement for structure, medication for appetite regulation.
Am I eligible for prescription weight loss medication on the NHS?
NHS eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions (diabetes, high blood pressure, heart disease). For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds may apply. Speak to your GP about referral to a specialist weight management service — they'll assess your individual situation.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections licensed for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trial data suggests Mounjaro may support slightly higher average weight loss (15–21% vs approximately 15%), but individual results vary. Your prescriber will advise which suits you best.
How quickly can I access prescription weight loss medication privately?
Private prescribing is typically faster than NHS routes. Following an online clinical assessment with a UK-licensed prescriber, a prescription can be issued within days if appropriate. Costs vary by dose and provider, generally between £129–£320 monthly. Always ensure you use a GPhC-registered pharmacy dispensing authentic medication.
Can I use meal replacement shakes alongside prescription weight loss medication?
Yes — many people combine structured meal planning with prescription medication. Meal replacements provide calorie control and convenience, while medications help regulate appetite. Always inform your prescriber of your full approach. The most effective weight loss combines medication (if prescribed), dietary changes, increased physical activity, and behaviour support.
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.