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 Weight Loss Injections in the UK
Semaglutide weight loss injections (brand name Wegovy) are prescription-only medicines available in the UK for adults living with obesity or overweight with weight-related health conditions. The NHS approves semaglutide through specialist tier 3 weight management services, though access varies significantly by region. This guide explains NHS eligibility criteria, how the weekly weight loss injection works, clinical evidence from the STEP trials, and how to access semaglutide through both NHS and private routes in the UK.
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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.
NHS Eligibility and Tier 3 Access for Semaglutide
In the UK, semaglutide (Wegovy) is available through NHS specialist tier 3 weight management services, not through standard GP prescription. Eligibility typically requires a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may be eligible at lower BMI thresholds due to higher health risks at these levels.
Access requires referral from your GP to your local integrated care board (ICB) tier 3 service. These multidisciplinary teams assess suitability, monitor your response, and support lifestyle changes alongside the weekly weight loss injection. However, NHS waiting lists are often lengthy—some areas have waiting times of several months or years. Use our GLP-1 weight loss calculator to explore potential weight loss projections, and our BMI calculator to check your eligibility threshold based on your personal measurements.
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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.
NHS vs Private: How to Access Semaglutide in the UK
NHS route: Free through tier 3 services once referred and approved, but involves waiting lists and regional variation in availability. Private route: Available through GPhC-registered online prescribers following a clinical assessment, typically within days, at a cost of approximately £129–£200 per month depending on dose. Both routes require a prescription from a UK-licensed healthcare professional—semaglutide is not available over the counter. The weekly semaglutide 2.4mg dose (maximum strength for weight loss) is the same in both NHS and private settings. Your GP can discuss which route may suit your circumstances, and you can track your progress using our free progress tracker regardless of which access route you choose.
- 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.
How much weight loss can I expect with semaglutide on the NHS?
Clinical trials (STEP-1) showed an average weight loss of approximately 14.9% body weight over 68 weeks on semaglutide 2.4mg, alongside dietary changes and increased physical activity. Individual results vary significantly. Your NHS tier 3 team will set realistic goals based on your health profile and monitor your progress at each clinic visit.
Is semaglutide the same as Ozempic?
Both contain the same active ingredient (semaglutide), but Ozempic is approved for type 2 diabetes management (up to 2mg) and is not licensed for weight loss in the UK. Wegovy is the branded semaglutide specifically approved for weight management and uses a higher dose (up to 2.4mg). Using Ozempic for weight loss would be off-label.
What are the main side effects of semaglutide weight loss injections?
Very common side effects include nausea, diarrhoea, constipation, and stomach pain, especially when starting or increasing doses. These often improve over time. Serious but rare side effects include pancreatitis (severe stomach pain) and gallbladder problems. Always inform your prescriber of any persistent or concerning symptoms.
Can I switch from Wegovy to another GLP-1 receptor agonist like Mounjaro?
Switching between GLP-1 medications requires guidance from your prescriber. While both are weekly weight loss injections, they work slightly differently. Mounjaro is a dual GIP and GLP-1 agonist, whereas semaglutide is a GLP-1 agonist only. Any switch must be managed by a healthcare professional to ensure safe dosing.
How long does semaglutide take to work?
Many people notice appetite reduction within days of the first injection, but meaningful weight loss typically becomes measurable after 4–8 weeks of consistent doses. The STEP trials measured results at 68 weeks, reflecting that semaglutide is designed as a sustained weight management tool, not a quick-fix treatment.
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.