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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Best Weight Loss Supplements in the UK
If you're looking for weight loss supplements in the UK, the most effective evidence-based options are prescription medications rather than over-the-counter supplements. The NHS recognises prescription weight loss injections like Wegovy (semaglutide) and Mounjaro (tirzepatide) as clinically proven options for weight management. These are typically prescribed through specialist weight management services for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. Over-the-counter supplements have limited evidence compared to prescription options. This guide covers what's actually available and supported by UK health guidance.
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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.
Prescription Weight Loss Options Available in the UK
The most effective weight loss supplements available through NHS and private prescription in the UK are GLP-1 receptor agonist injections. Wegovy (semaglutide) is a once-weekly injection licensed for weight management. In clinical trials, participants taking Wegovy lost an average of approximately 15% of their body weight over 68 weeks — though individual results vary significantly. Mounjaro (tirzepatide) works differently as a dual GIP and GLP-1 agonist, with clinical trials showing average weight loss of 15–21% depending on dose.
Both require a prescription from a UK-licensed prescriber following a clinical assessment. Access through the NHS involves referral to specialist tier 3 weight management services, though waiting times vary by region. Private prescribing is also available through registered online pharmacies. These medications work by reducing appetite, helping you feel fuller after smaller meals, and slowing how quickly food leaves your stomach. They're used alongside a reduced-calorie diet and increased physical activity — not instead of lifestyle changes.
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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.
Over-the-Counter Supplements and Lifestyle Approaches
Many over-the-counter weight loss supplements are available in UK shops and online, but few have strong clinical evidence supporting their effectiveness for significant weight loss. Products containing caffeine, green tea extract, or conjugated linoleic acid (CLA) show modest effects at best. The NHS recommends sustainable weight loss of 0.5–1 kg per week through calorie deficit, which typically requires reducing intake by around 500 kcal daily.
For genuine weight management support in the UK, start by calculating your personal BMI using our free BMI calculator to understand your health category. Track your progress with our free progress tracker, and use our GLP-1 weight loss calculator to estimate potential outcomes if you're considering prescription options. Your GP can assess whether prescription weight loss medication is appropriate for you based on your individual health and 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 weight loss supplements and prescription weight loss medication?
Over-the-counter supplements have limited clinical evidence for weight loss. Prescription medications like Wegovy and Mounjaro are NHS-licensed, clinically proven through large trials, and require medical assessment. Prescription options show weight loss of 15–21% on average, while most supplements show minimal effects.
Is Wegovy available on the NHS in the UK?
Wegovy can be prescribed through NHS specialist weight management services (tier 3), but availability varies significantly by region and waiting lists can be lengthy. Private prescription through registered online pharmacies is also available following a clinical assessment with a licensed prescriber.
How much weight can you lose with prescription weight loss medication?
Clinical trials show Wegovy users lost approximately 15% of body weight on average, while Mounjaro users lost 15–21% depending on dose. However, results vary between individuals. Weight loss is achieved alongside a reduced-calorie diet and increased physical activity.
Do I need a prescription for weight loss supplements in the UK?
Over-the-counter supplements don't require a prescription. However, the most effective prescription weight loss options (Wegovy, Mounjaro) do require a prescription from a UK-licensed prescriber following a clinical assessment of your health and BMI.
What's the NHS position on weight loss supplements?
The NHS recommends evidence-based approaches including calorie deficit, diet, and physical activity first. For BMI 30+, or BMI 27+ with health conditions, NHS specialist services may prescribe licensed weight loss medications like Wegovy or Mounjaro as part of comprehensive weight management.
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.