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
What Does Semaglutide Do? NHS Overview
Semaglutide is a prescription-only GLP-1 receptor agonist injection licensed in the UK for weight management under the brand name Wegovy. It works by mimicking a natural hormone that helps regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. In the UK, semaglutide is approved by the MHRA and prescribed through NHS specialist weight management services or private online prescribers following clinical assessment. This guide explains how semaglutide works, how it's accessed through the NHS, and what NHS guidance says about its use.
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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 NHS Eligibility
Semaglutide is a GLP-1 receptor agonist—a medication class that activates the GLP-1 hormone pathway. This natural hormone, produced in the gut after eating, signals to your brain that you're full and helps regulate blood sugar. Semaglutide amplifies these effects, which may help reduce appetite and support weight loss alongside dietary changes and increased physical activity.
In clinical trials (STEP studies), semaglutide at the maximum dose of 2.4 mg once weekly helped participants lose an average of approximately 15% of their body weight over 68 weeks—though individual results vary significantly. The NHS and NICE have approved semaglutide for weight management in UK adults who meet eligibility criteria.
NHS eligibility for semaglutide (Wegovy):
- BMI of 30 kg/m² or above (obesity), OR
- BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, sleep apnoea, or cardiovascular disease)
- Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may be eligible at a lower BMI threshold (27.5 or above)
- Age 18 and above
Use our free BMI calculator above to check whether you may fall within the eligible range, and our GLP-1 weight loss calculator to estimate potential results at different doses.
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.
Accessing Semaglutide Through the NHS vs Private Route
In the UK, semaglutide is available through two routes. NHS access is through tier 3 specialist weight management services—your GP can refer you, but these services have significant waiting lists in many areas and availability varies by region. Private access is through GPhC-registered online prescribers following an online clinical assessment; this route does not require an NHS referral and is available immediately.
Both routes require a clinical assessment to confirm you're eligible and that semaglutide is safe for you. Semaglutide is always a prescription-only medication and is most effective when combined with a reduced-calorie diet and increased physical activity. Your GP can advise on which route is most appropriate for your circumstances, and you can use our weight converter to track your progress in stone, pounds, or kilograms as you lose weight.
- 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 Ozempic?
Both contain semaglutide, but Ozempic (up to 2 mg) is approved for type 2 diabetes management. Wegovy (up to 2.4 mg) is the licensed weight management version in the UK. Using Ozempic for weight loss is off-label and not recommended. Always use the medication prescribed by your healthcare provider.
How quickly will I lose weight on semaglutide?
Weight loss varies individually, but clinical trials showed an average loss of about 15% body weight over 68 weeks at the highest dose. The NHS recommends losing 0.5–1 kg per week as a safe, sustainable rate. Use our weight loss calculator to estimate potential outcomes based on dose and your current weight.
What are the main side effects of semaglutide?
Very common side effects include nausea, diarrhoea, vomiting, and constipation—usually mild and temporary. Less common side effects include headache, fatigue, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) or allergic reactions. Always report any concerns to your GP.
Can I get semaglutide free on the NHS?
Yes, if prescribed through an NHS tier 3 specialist weight management service, semaglutide is free on the NHS. However, waiting lists are long in many areas. Private prescriptions cost £129–£320 per month depending on dose. Your GP can advise on NHS availability in your area and referral process.
Do I need to follow a specific diet while taking semaglutide?
Semaglutide works best alongside a reduced-calorie diet and increased physical activity. There's no single prescribed diet—your prescriber may recommend working with a dietitian. NHS guidelines emphasize sustainable, long-term lifestyle changes rather than restrictive dieting for best results.
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.