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
Free tracker included with every download this week
How to Buy Weight Loss Medication in the UK
Weight loss medication is available in the UK through both NHS and private routes, but all prescription weight loss drugs require a clinical assessment before you can buy them. The most commonly prescribed options are GLP-1 receptor agonist injections like Wegovy (semaglutide) and Mounjaro (tirzepatide), which help reduce appetite and support sustainable weight management alongside diet and physical activity. This guide explains your options, eligibility criteria, and how to access prescription weight loss medication safely 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.
How Weight Loss Medication Works in the UK
Weight loss injections work by activating natural hormone pathways that regulate appetite and food intake. Wegovy (semaglutide) is a GLP-1 receptor agonist — a once-weekly injection that helps you feel fuller after smaller meals and reduces cravings. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, also injected once weekly, which may offer additional appetite suppression through two hormone pathways. Both are prescription-only medicines licensed for weight management in UK adults. In the STEP clinical trial, Wegovy helped participants lose an average of around 15% of their body weight over 68 weeks when combined with diet and exercise. Results vary significantly between individuals — some lose more, some less. These medications are not suitable for everyone and require a prescriber's assessment to confirm eligibility.
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 — How to Buy
NHS access: You can be referred to a tier 3 specialist weight management service by your GP if you meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions). NHS services provide assessment, prescription, and monitoring. However, waiting lists vary significantly by region — some areas have waits of many months or years. Private access: GPhC-registered online pharmacies offer weight loss medication following an online clinical assessment with a UK-licensed prescriber. This route is faster and does not require an NHS referral, but costs typically range from £129–£320 per month depending on dose. Use our BMI calculator to check your starting point, and our GLP-1 weight loss calculator to estimate potential results at different doses before you commit to treatment.
- 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.
Who is eligible to buy weight loss medication in the UK?
Adults with a BMI of 30 or above, or 27–29.9 with weight-related conditions (type 2 diabetes, high blood pressure, sleep apnoea, cardiovascular disease), may be eligible. Lower BMI thresholds apply to South Asian, Chinese, Black African, and Black Caribbean populations. You must be aged 18+ and not pregnant. A prescriber will assess your individual health before prescribing.
What's the difference between Wegovy and Mounjaro?
Both are once-weekly injections for weight management in the UK. Wegovy (semaglutide) is a GLP-1 agonist; Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist. Clinical trials showed Mounjaro produced slightly higher average weight loss (around 15–21% of body weight) versus Wegovy (around 15%), though individual results vary. Costs and availability also differ between providers.
How long does it take to see weight loss results?
Weight loss typically becomes noticeable after 4–8 weeks of consistent use, though individual timelines vary. The medication works best alongside a reduced-calorie diet and increased physical activity. Track your progress using our free progress tracker to monitor changes week by week. Sustainable weight loss is gradual — around 0.5–1 kg per week is typical and recommended.
Can I buy weight loss medication without a prescription in the UK?
No. Wegovy, Mounjaro, and other weight loss injections are prescription-only medicines in the UK. You cannot buy them over the counter. You must obtain a prescription from a UK-licensed GP or prescriber following a clinical assessment. This ensures the medication is safe and appropriate for your individual health.
What happens after I buy weight loss medication — do I need monitoring?
Yes. Both NHS and private providers monitor your progress, side effects, and health markers while you're taking prescription weight loss medication. Your prescriber may ask you to report regularly on weight changes, appetite, and any side effects. This monitoring helps ensure the medication remains safe and effective for you personally.
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.