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 GLP-1 Supplement for Weight Loss in the UK
If you're searching for the best GLP-1 supplement for weight loss in the UK, you're likely looking at prescription weight loss medications rather than over-the-counter supplements. Three prescription-only GLP-1 and GIP receptor agonist medications are currently licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These are evidence-based prescription medications, not supplements, and they require a clinical assessment and GP prescription or private online consultation before you can access them. This guide explains how they work, who's eligible, and the difference between NHS and private pathways for weight loss medication in the UK.
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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 Weight Loss Medications Explained
Mounjaro (tirzepatide) is a once-weekly injection that works as a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to help regulate appetite and support weight management. Clinical trials showed participants lost an average of 15–21% of their body weight — though individual results vary significantly. Wegovy (semaglutide) is also a once-weekly injection but activates only the GLP-1 pathway; clinical trials showed average weight loss of around 15% body weight. Saxenda (liraglutide) is a daily injection with similar effects but requires injecting every day rather than once weekly.
- All three are prescription-only medicines requiring a clinical assessment
- All must be used alongside a reduced-calorie diet and increased physical activity
- Side effects are common (nausea, diarrhoea, constipation) but usually improve over time
- Results vary — weight loss is not assured, and individual factors affect outcomes
- Use our GLP-1 weight loss calculator to estimate potential results at different doses
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.
NHS vs Private Access and Eligibility in the UK
In the UK, you may be eligible for weight loss medication if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). Lower BMI thresholds apply for people of South Asian, Chinese, Black African, or Black Caribbean heritage.
NHS access: Through specialist tier 3 weight management services — requires GP referral and can involve long waiting lists depending on your region. Private access: Through a UK-licensed prescriber via an online consultation with a GPhC-registered pharmacy — faster but costs apply (typically £129–£320+ per month depending on dose).
Check your BMI using our free BMI calculator, then speak to your GP about whether prescription weight loss medication might be right for you.
- 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 GLP-1 supplements available over the counter in the UK?
No. Mounjaro, Wegovy, and Saxenda are all prescription-only medicines in the UK. They are not supplements and cannot be bought without a prescription from a UK-licensed prescriber. Avoid any retailer claiming to sell these medications without a prescription — they would not be legal or safe.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. Mounjaro showed slightly higher average weight loss in trials (15–21% vs 15%), but individual results vary. Both are once-weekly injections. Any choice between them should be made by a prescriber based on your health profile.
How long does it take to see weight loss results with GLP-1 medication?
Most people begin to notice changes in appetite within 1–2 weeks of starting. Measurable weight loss typically appears within 4–8 weeks, though this varies. Full effects are usually seen after 16–20 weeks of treatment. Consistency with diet and activity changes is essential alongside medication.
Can I get GLP-1 weight loss medication on the NHS?
Yes, through NHS specialist tier 3 weight management services if you meet eligibility criteria and are referred by your GP. However, availability and waiting times vary significantly by region. Contact your GP to ask about local services and waiting lists in your area.
What happens to weight if I stop taking GLP-1 medication?
Weight typically returns gradually over time if you stop taking the medication without sustaining the lifestyle changes (diet and exercise) that supported the initial loss. This is why GLP-1 medications are most effective when combined with long-term dietary and activity changes, not as a standalone solution.
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.