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 Injection for Weight Loss in the UK
Semaglutide is a prescription-only injection licensed in the UK for weight management in adults. Marketed as Wegovy, this GLP-1 receptor agonist is available through both NHS specialist services and private prescribers. Clinical trials showed that semaglutide 2.4mg helped people lose an average of 15% of their body weight when used alongside a reduced-calorie diet and increased physical activity. This guide covers NHS eligibility, how the weekly weight loss injection works, and your options for accessing treatment 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.
NHS Eligibility and Tier 3 Weight Management Services
In the UK, semaglutide (Wegovy) is available through NHS tier 3 specialist weight management services for adults who meet specific criteria. You must have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, high blood pressure, abnormal blood fats, or obstructive sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds — eligibility may start at BMI 27.5 or above due to higher cardiovascular risk at lower weights.
Access requires referral from your GP to your local integrated care board (ICB) tier 3 service. NICE has approved semaglutide for NHS use in specialist weight management, but regional availability varies significantly. Waiting times can be substantial in many areas — some services have 12–18 month waiting lists. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and our BMI calculator to check your current eligibility status.
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 to Semaglutide in the UK
NHS route: Free on prescription through tier 3 services, but requires GP referral and may involve lengthy waits. Your GP cannot prescribe Wegovy directly; it must come through specialist weight management services.
Private route: Available without NHS referral through GPhC-registered online prescribers. A UK-licensed doctor assesses your eligibility via online consultation. If approved, the prescription is dispensed by a regulated pharmacy. Private semaglutide typically costs £129–£250/month depending on dose. There are no waiting lists, and treatment can start within days.
Both routes require a clinical assessment — semaglutide is not suitable for everyone. Track your progress with our free progress tracker once you begin 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.
What is the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic is approved for type 2 diabetes (doses up to 2mg) and is not licensed for weight loss in the UK. Wegovy is specifically approved for weight management and uses higher doses up to 2.4mg. Using Ozempic for weight loss would be off-label — Wegovy is the correct licensed product.
How much weight can I expect to lose with semaglutide?
Clinical trials (STEP-1) showed that on average, adults lost approximately 15% of body weight over 68 weeks at the maximum 2.4mg dose, alongside a reduced-calorie diet and exercise. Individual results vary significantly — some lose more, some less. Results depend on adherence, lifestyle changes, and individual metabolism.
Is semaglutide a GLP-1 receptor agonist?
Yes. Semaglutide works by activating the GLP-1 hormone pathway, which reduces appetite, supports feeling fuller after meals, and slows gastric emptying. It's a once-weekly injectable medication. Novo Nordisk manufactures both the diabetes version (Ozempic) and the weight loss version (Wegovy).
What are the most common side effects of semaglutide?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — especially when first starting or increasing doses. These usually improve over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and serious allergic reactions. Always report new or worsening symptoms to your prescriber.
Can I get semaglutide on the NHS quickly?
NHS access is through tier 3 specialist services, which often have long waiting lists (sometimes 12+ months). If you need treatment urgently, the private route may be faster — you can be assessed and prescribed within days. Discuss both options with your GP, who can provide a referral to your local tier 3 service.
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.