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 Supplements That Work — What's Available in the UK
When searching for weight loss supplements that work, many UK adults don't realise that prescription weight management medications are available through the NHS and private healthcare. Unlike over-the-counter supplements with limited evidence, prescription GLP-1 medications have strong clinical trial data showing significant weight loss results. This guide explains which evidence-based options are available in the UK, who is eligible, and how to access them through your GP or a licensed prescriber.
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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 — Prescription Options
The most effective weight loss supplements with clinical evidence in the UK are prescription GLP-1 receptor agonist medications. Three are currently licensed for weight management:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 agonist. Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks. Maximum dose is 15 mg once weekly.
- Wegovy (semaglutide) — A GLP-1 agonist. Clinical trials showed an average weight loss of approximately 15% of body weight. Maximum dose is 2.4 mg once weekly.
- Saxenda (liraglutide) — A GLP-1 agonist administered daily. Average weight loss of around 5–7% of body weight in clinical trials.
These medications work by mimicking natural gut hormones that regulate appetite and blood sugar. Individual results vary, and they work best alongside a reduced-calorie diet and increased physical activity. All three are prescription-only and require clinical assessment before being prescribed. Use our GLP-1 weight loss calculator to estimate potential results at different doses, and try our BMI calculator to check if you may be eligible for treatment.
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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 — How to Get Started
In the UK, you can access weight loss medication through two routes. The NHS route involves referral to a tier 3 specialist weight management service from your GP. However, NHS availability varies significantly by region and waiting lists can be lengthy in many areas. The private route involves an online consultation with a UK-licensed prescriber and prescription from a GPhC-registered pharmacy, typically costing £129–£320 per month depending on dose.
To find out if you're eligible, calculate your BMI using the free BMI calculator on this page. Adults with a BMI of 30 or above, or 27 or above with weight-related health conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea), may be eligible. Speak to your GP about NHS weight loss services in your area, or explore private prescribing options. Either way, a healthcare professional will assess your suitability based on your individual health history. Track your progress with our free progress tracker once you begin any weight management programme.
- 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.
Do weight loss supplements actually work in the UK?
Over-the-counter supplements have limited clinical evidence. However, prescription GLP-1 medications like Mounjaro and Wegovy are evidence-based and show significant results — averaging 15–clinically studied weight loss in clinical trials. Results vary individually and require lifestyle changes alongside medication.
What is the difference between Mounjaro and Wegovy?
Both are prescription-only GLP-1 medications, but Mounjaro is a dual GIP/GLP-1 agonist (max 15 mg weekly) while Wegovy is a single GLP-1 agonist (max 2.4 mg weekly). Clinical trials suggest Mounjaro may produce slightly greater average weight loss, though individual responses vary significantly.
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 conditions like diabetes or high blood pressure. Eligibility varies by region. Contact your GP for referral to a tier 3 weight management service in your area. Waiting times vary considerably.
Can I get weight loss medication privately in the UK?
Yes. Private prescribing is available through UK-licensed prescribers via online consultation and GPhC-registered pharmacies. No NHS referral is needed. Costs range from approximately £129–£320 per month depending on dose. A clinical assessment is still required before prescription.
How quickly will I lose weight on prescription weight loss medication?
Safe weight loss is typically 0.5–1 kg per week. With GLP-1 medications, clinical trials showed average losses of 15–21% of body weight over 12–18 months. However, results are highly individual and depend on adherence to diet, physical activity, and the specific medication and dose used.
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.