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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Wegovy Weight Loss Injection — How It Works
Wegovy is a prescription-only weekly weight loss injection licensed in the UK for adults with excess weight and weight-related health conditions. It contains semaglutide, a GLP-1 receptor agonist that works by reducing appetite, helping you feel fuller after smaller meals, and slowing how quickly food leaves your stomach. Clinical trials showed that people using Wegovy, alongside a reduced-calorie diet and increased physical activity, lost an average of around 15% of their body weight — though individual results vary significantly. This guide explains how it works, who's eligible, and what to expect.
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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 Wegovy Works and What to Expect
Wegovy works by mimicking a natural hormone called GLP-1 (glucagon-like peptide-1) that your gut produces after eating. This hormone signals to your brain that you're full, reduces food cravings, and slows gastric emptying — meaning food stays in your stomach longer, keeping you satisfied for longer. Wegovy is a once-weekly semaglutide injection, unlike some other weight loss treatments that require daily doses.
The starting dose is 0.25 mg, with gradual increases over approximately 16 weeks to reach the maximum dose of 2.4 mg. Each dose increase happens over 4 weeks, giving your body time to adjust. In the STEP-1 clinical trial, participants on the 2.4 mg dose lost an average of 14.9% of their body weight over 68 weeks, alongside lifestyle changes. It's important to understand that Wegovy is not a assured solution — it works best when combined with a reduced-calorie diet, regular physical activity, and sustained behaviour change. Individual responses vary, and some people may experience more weight loss than others.
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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.
Wegovy Eligibility, Doses, and Access in the UK
You may be eligible for Wegovy if you 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, prediabetes, high blood pressure, or cardiovascular disease. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may have lower thresholds due to higher health risks at lower BMI levels.
In the UK, Wegovy is available through NHS specialist tier 3 weight management services (following a GP referral) or through private online prescribing with a UK-licensed prescriber. Access varies significantly by region and waiting times can be lengthy on the NHS. Private prescribing typically requires an online clinical assessment to confirm suitability. Wegovy is prescription-only — it cannot be purchased without a valid prescription from a licensed healthcare professional.
- 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 can you lose with Wegovy?
Clinical trials showed an average weight loss of around 15% of body weight at the maximum dose (2.4 mg) over 68 weeks, alongside diet and exercise changes. Individual results vary significantly — some people lose more, some less. Results depend on adherence, lifestyle changes, metabolism, and other personal factors. Your prescriber can discuss realistic expectations based on your individual circumstances.
Is Wegovy the same as Ozempic?
Both Wegovy and Ozempic contain semaglutide, but they are different products. Ozempic is licensed for type 2 diabetes management (doses up to 2 mg). Wegovy is specifically licensed for weight management (doses up to 2.4 mg). Using Ozempic for weight loss is off-label in the UK — Wegovy is the licensed weight management option. Never swap between them without prescriber guidance.
What are the common side effects of Wegovy?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — often mild and temporary as your body adjusts. Other common effects include indigestion, headache, fatigue, dizziness, and injection site reactions. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or gallbladder problems. Always report new or worsening symptoms to your prescriber.
How do I use Wegovy and where do I inject it?
Wegovy comes in pre-filled pens for self-injection once weekly, on the same day each week. Common injection sites are the stomach (abdomen), upper thigh, or upper arm. Rotate sites each week. Store unopened pens in a refrigerator (2–8°C). After first use, you can keep your pen at room temperature below 30°C for up to 30 days. Always follow the instructions provided with your specific pen.
Can I get Wegovy on the NHS in the UK?
Yes, Wegovy is available through NHS specialist weight management services (tier 3), but access varies significantly by region. You'll need a GP referral and assessment by a specialist team. Waiting times can be several months or longer in many areas. Alternatively, Wegovy is available privately through online prescribing services following a clinical assessment. Your prescriber will confirm suitability and discuss costs.
Ready to take control of your weight loss journey?
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