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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Semaglutide in the UK: Everything You Need to Know
Semaglutide is a prescription-only medication licensed in the UK for weight management under the brand name Wegovy. It's a GLP-1 receptor agonist — a type of injection that helps regulate appetite and may support weight loss alongside lifestyle changes. This guide explains how semaglutide works in the UK, who may be eligible, what to expect, and how it differs from similar medications. Use our free GLP-1 weight loss calculator to explore potential outcomes, or our BMI calculator to assess your current health context.
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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 Semaglutide Works and What Makes It Different
Semaglutide mimics a natural hormone called GLP-1 (glucagon-like peptide-1) that your body produces after eating. It helps regulate appetite by signalling fullness to the brain, slowing how quickly food leaves your stomach, and supporting better blood sugar control. This single mechanism differs from dual-action medications like tirzepatide (Mounjaro), which activates both GIP and GLP-1 pathways.
In clinical trials (STEP-1):
- Participants taking semaglutide 2.4mg lost an average of approximately 15% of their body weight over 68 weeks
- Results were achieved alongside a reduced-calorie diet and increased physical activity
- Weight loss is not assured — individual results vary significantly
- Common side effects include nausea, diarrhoea, constipation, and stomach pain, typically reducing over time
Semaglutide is available as Wegovy (weight management) or Ozempic (type 2 diabetes). Important: Ozempic is not licensed for weight loss in the UK — Wegovy is the approved weight management version.
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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.
UK Eligibility, Doses, and Access Routes
NHS eligibility: You may be eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply. Access is through tier 3 specialist weight management services — refer to your GP to be assessed.
Doses: Semaglutide starts at 0.25mg weekly, increasing gradually to a maximum of 2.4mg weekly. Private access: Available through GPhC-registered online prescribers following a clinical assessment, without needing an NHS referral. Try our free weight loss calculator to explore different dose outcomes, or use the BMI calculator to determine your current weight management context.
- 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.
Is semaglutide the same as Wegovy?
Semaglutide is the active ingredient; Wegovy is the brand name for semaglutide 2.4mg approved for weight loss in the UK. Ozempic is also semaglutide but at a lower dose and is licensed for type 2 diabetes, not weight loss. Always use the brand name your prescriber specifies.
What's the difference between semaglutide and tirzepatide?
Semaglutide (Wegovy) is a single GLP-1 agonist. Tirzepatide (Mounjaro) is a dual GIP and GLP-1 agonist. In clinical trials, tirzepatide showed slightly higher average weight loss (15–21% vs 15%), but both are effective. Your prescriber will assess which is most suitable.
How much weight can I expect to lose with semaglutide?
Clinical trials showed average weight loss of approximately 15% of body weight at the maximum dose, alongside diet and exercise changes. Individual results vary considerably — some people lose more, some less. Weight loss is not assured. Use our free GLP-1 calculator to explore potential outcomes for your situation.
What are the common side effects of semaglutide?
Very common side effects include nausea, diarrhoea, vomiting, and constipation. These are usually temporary and tend to decrease over time as your body adjusts. Less common side effects include fatigue, dizziness, and injection site reactions. Always discuss side effects with your prescriber.
Can I get semaglutide on the NHS in the UK?
Yes, through specialist tier 3 weight management services if you meet eligibility criteria. Waiting lists vary by region — some areas have very long queues. You can also access semaglutide privately through GPhC-registered online prescribers following a clinical assessment, without an NHS referral. Your GP can discuss both options.
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.