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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Understanding Wegovy and Semaglutide for Weight Loss in the UK
Wegovy and Ozempic both contain the same active ingredient — semaglutide — but they're licensed for different purposes in the UK. Wegovy is the prescription-only weight management injection, while Ozempic is approved for type 2 diabetes and is not licensed for weight loss. This UK health guide explains how semaglutide works, what the clinical evidence shows, and how to access Wegovy through the NHS or private prescribing.
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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.
How Semaglutide Works and the Difference Between Wegovy and Ozempic
Semaglutide is a GLP-1 receptor agonist — a medication that mimics the glucagon-like peptide-1 hormone produced naturally in your gut. This hormone helps regulate appetite, blood sugar, and how quickly food leaves your stomach. Wegovy (semaglutide 2.4 mg) is licensed specifically for weight management in UK adults, while Ozempic (semaglutide up to 2 mg) is approved for type 2 diabetes control. Using Ozempic for weight loss is off-label and not recommended as standard practice in the UK.
In the STEP-1 clinical trial, adults taking Wegovy 2.4 mg alongside a reduced-calorie diet and increased physical activity lost an average of approximately 14.9% of their body weight over 68 weeks — though individual results vary significantly. Semaglutide works by:
- Reducing appetite and food cravings
- Helping you feel fuller after smaller meals
- Slowing gastric emptying (digestion speed)
- Supporting better blood sugar control
It is not insulin and works differently from diabetes medications.
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.
UK Eligibility, Doses, and How to Access Wegovy
In the UK, Wegovy may be prescribed for adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions including type 2 diabetes, high blood pressure, or cardiovascular disease. Wegovy is prescription-only and requires a clinical assessment before dispensing. Access is available through NHS specialist tier 3 weight management services (with potential long waiting lists depending on your region) or through private online prescribing with a UK-licensed prescriber.
Wegovy doses start at 0.25 mg weekly and escalate every 4 weeks up to 2.4 mg — the maximum maintenance dose. Use our free BMI calculator to check if you fall within the eligible range, and our GLP-1 weight loss calculator to see projected outcomes at different doses.
Common side effects include nausea, diarrhoea, constipation, and stomach discomfort — usually mild and improving over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Semaglutide may reduce absorption of oral contraceptives; women using oral contraception should add a barrier method for 4 weeks after starting and after each dose increase. Always inform your prescriber of all medications you take, and speak to your GP if you experience severe or persistent side effects.
- 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's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Wegovy (2.4 mg) is licensed for weight management, while Ozempic (up to 2 mg) is approved for type 2 diabetes. Using Ozempic for weight loss is off-label and not standard practice in the UK. Wegovy is the licensed weight loss version.
How much weight can you lose on Wegovy?
Clinical trials showed participants lost an average of about 14.9% of body weight over 68 weeks at the maximum dose (2.4 mg), alongside dietary changes and exercise. Individual results vary significantly — some lose more, some less — and weight loss depends on adherence and lifestyle changes.
Is Wegovy available on the NHS in the UK?
Wegovy is available through NHS specialist tier 3 weight management services for eligible adults, but access and waiting times vary widely by region. Private access is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber.
What are the main side effects of Wegovy?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — usually mild and improving over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Tell your GP if side effects persist or worsen.
Can you take Wegovy with other medications?
Semaglutide may reduce absorption of oral contraceptives — women using oral birth control should add a barrier method for 4 weeks after starting and after each dose increase. Always inform your prescriber of all medications. Your prescriber can assess interactions specific to your health situation.
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.