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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What supplements aid weight loss in the UK?
While many supplements claim to support weight loss, the most effective evidence-based options available to eligible UK adults are prescription medications rather than over-the-counter supplements. If you're looking for serious weight management support, prescription weight loss injections and medications approved by the MHRA offer clinical evidence of effectiveness. This guide explains your options and how to find out if you're eligible for prescription-based weight management through the NHS or private prescribing.
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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 prescription weight loss medications
For adults meeting specific eligibility criteria, the UK has three MHRA-approved prescription medications for weight management — all with stronger clinical evidence than typical dietary supplements:
- Mounjaro (tirzepatide) — a once-weekly injection licensed for weight management. Clinical trials showed participants lost an average of 15–21% of body weight over 72 weeks when combined with a reduced-calorie diet and physical activity.
- Wegovy (semaglutide) — also a once-weekly injection. Clinical evidence demonstrates average weight loss of approximately 15% body weight at the maximum dose.
- Saxenda (liraglutide) — a once-daily injection. Evidence supports modest weight loss, typically 5–10% body weight reduction.
All three are prescription-only medicines available in the UK for weight management in adults with a BMI of 30 kg/m² or above, or 27 kg/m² or above with weight-related health conditions such as type 2 diabetes or high blood pressure. Our free GLP-1 weight loss calculator can help you understand how these medications work and estimate potential outcomes based on your starting weight.
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 versus private access and eligibility
In the UK, prescription weight loss medication is accessed through two routes. NHS access is via specialist tier 3 or tier 4 weight management services — your GP can refer you, though waiting lists vary significantly by region and may be lengthy. Private access is available through UK-licensed prescribers following an online clinical assessment; you do not need an NHS referral. Eligibility for both routes requires a BMI of 30 (or 27 with weight-related health conditions), though for people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds may apply. Your GP can advise whether you meet criteria or discuss private options. Use our free BMI calculator above to check your starting point and inform that conversation.
- 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 there supplements that work as well as prescription weight loss medication?
No. Over-the-counter supplements have minimal clinical evidence compared to prescription medications like Mounjaro and Wegovy. Prescription GLP-1 receptor agonists are the most researched weight management options available in the UK, showing weight loss of 15–21% in clinical trials. Supplements typically show modest or no meaningful weight loss benefit.
Who is eligible for prescription weight loss medication in the UK?
Adults with a BMI of 30 kg/m² or above, or a BMI of 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, obstructive sleep apnoea, or cardiovascular disease). Those of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at lower BMI thresholds. A prescriber assesses individual eligibility following clinical assessment.
Can I get weight loss medication through my GP on the NHS?
Your GP can discuss weight management options and refer you to specialist NHS weight management services (tier 3 or 4), where prescription medications may be initiated. However, NHS availability varies significantly by region, and waiting times can be substantial. Private prescribing is an alternative route that does not require an NHS referral.
What is the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections. Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1) and shows average weight loss of 15–21%. Wegovy (semaglutide) activates one pathway (GLP-1 only) with average weight loss around 15%. Individual results vary. A prescriber will assess which is most suitable for your circumstances.
How much weight can I expect to lose with prescription weight loss medication?
Clinical trials show average weight loss of 15–21% body weight with Mounjaro and around 15% with Wegovy over several months — though individual results vary significantly. Weight loss medication works alongside a reduced-calorie diet and increased physical activity, not instead of them. Our weight loss projection calculator can help estimate potential outcomes based on your starting weight.
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.