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
Wegovy Pen UK — How the Weekly Injection Works
Wegovy is a prescription-only weight loss injection available in the UK for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. The medication comes as a pre-filled pen that you inject once weekly under your skin. It contains semaglutide, a GLP-1 receptor agonist that works by reducing appetite and helping you feel fuller after smaller meals. Access is available through NHS specialist weight management services or private prescribing following clinical assessment.
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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 Wegovy Works and What to Expect
Wegovy (semaglutide) activates the GLP-1 hormone pathway in your body, which naturally signals fullness to your brain. This helps reduce cravings, supports eating smaller portions, and slows how quickly food leaves your stomach. Clinical trials showed participants using Wegovy lost an average of approximately 15% of their body weight over 68 weeks — though individual results vary significantly.
The Wegovy pen is pre-filled and easy to use. You inject once per week under the skin (abdomen, thigh, or upper arm). Treatment starts at 0.25 mg and increases gradually over 16 weeks to the maximum maintenance dose of 2.4 mg. Each pen contains four doses. Most people experience side effects like nausea or changes in digestion during the first few weeks, which typically ease as your body adjusts. Try our GLP-1 weight loss calculator to see potential weight loss projections at different doses.
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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 and How to Access Wegovy
You're eligible for Wegovy in the UK if you have a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds (27.5+) due to higher health risks at these levels.
NHS access: Your GP can refer you to a tier 3 specialist weight management service, though waiting times vary by region. Private access: GPhC-registered online prescribers can assess you and issue a prescription if appropriate, typically within days. Both routes require a clinical assessment to confirm Wegovy is suitable for your individual health. Calculate your BMI using our free BMI calculator to check where you fall on NHS thresholds.
- 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 Wegovy the same as Ozempic?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (up to 2 mg dose) and using it for weight loss is off-label. Wegovy is specifically licensed for weight management in UK adults and contains a higher maximum dose (2.4 mg). Always use the medication as prescribed.
What are the main side effects of Wegovy?
Very common side effects include nausea, diarrhoea, vomiting, and constipation, especially in the first few weeks. Common side effects include indigestion, headache, fatigue, dizziness, and injection site reactions. Most ease over time. Seek urgent medical attention for severe stomach pain or serious allergic reactions.
How much weight will I lose on Wegovy?
Clinical trials showed average weight loss of approximately 15% of body weight, but individual results vary significantly based on your diet, activity level, and personal metabolism. Some people lose more, some less. Weight loss happens alongside reduced-calorie diet and increased physical activity — the medication supports these changes, not replaces them.
Can I get Wegovy through the NHS?
Yes, through NHS tier 3 specialist weight management services. Your GP can refer you, though waiting times vary considerably by region (ICB). Some areas have long waiting lists. Private prescribing offers faster access through online clinical assessments with UK-licensed prescribers, though you'll pay privately.
How do I store my Wegovy pen?
Unopened pens must be refrigerated at 2–8°C and kept in their original carton. Do not freeze. After first use, the pen can be stored at room temperature (below 30°C) for up to 30 days, then discarded. Keep away from heat and direct sunlight. Always check the expiry date before use.
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.