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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What Is Wegovy and How Does It Work?
Wegovy is a prescription-only weight management injection containing semaglutide, a GLP-1 receptor agonist licensed in the UK for adults with excess weight. It's a once-weekly injection that works by activating natural hunger-regulating hormones in your gut, helping you feel fuller after smaller meals. Clinical trials showed that adults 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, UK eligibility, doses, and how it compares to Mounjaro.
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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 Makes It Different From Mounjaro
Wegovy contains semaglutide, a GLP-1 receptor agonist — this means it activates a single natural hormone pathway (GLP-1) to regulate appetite and blood sugar. In contrast, Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two pathways simultaneously.
Both medications work by: slowing how quickly food leaves your stomach, signalling fullness to your brain, and reducing cravings. However, clinical trial data shows slightly different outcomes. The STEP-1 trial showed Wegovy helped patients lose approximately 14.9% of body weight at the maximum 2.4 mg dose. The SURMOUNT-1 trial showed Mounjaro achieved approximately 15–clinically studied weight loss depending on dose (5 mg to 15 mg).
Important: These are clinical trial averages. Individual results depend on diet, exercise, genetics, and how your body responds to the medication. A prescriber will discuss which option may suit your circumstances during a clinical assessment.
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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.
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UK Eligibility, Doses, and How to Access Wegovy
In the UK, Wegovy is available for adults with a BMI of 30 kg/m² or above, or BMI of 27–29.9 kg/m² with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or cardiovascular disease). Lower eligibility thresholds apply for adults of South Asian, Chinese, Black African, or Black Caribbean heritage.
Wegovy doses range from 0.25 mg to 2.4 mg, taken once weekly. Access in the UK is through two routes: NHS specialist tier 3 weight management services (via GP referral, though availability and waiting times vary significantly by region) or private online prescribing following a clinical assessment with a UK-licensed prescriber. Use our free GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to check your starting point.
- 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 main difference between Wegovy and Mounjaro?
Wegovy (semaglutide) is a single GLP-1 receptor agonist. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways instead of one. Clinical trials suggest Mounjaro may achieve slightly higher weight loss on average, but individual results vary. Your prescriber will assess which is more suitable during your clinical consultation.
Is Wegovy available on the NHS in the UK?
Yes, Wegovy is available through NHS specialist weight management services (tier 3). However, you need a GP referral and availability varies significantly by region — waiting lists can be lengthy in many areas. Private access is also available through GPhC-registered online pharmacies following an online clinical assessment.
How much weight can I expect to lose on Wegovy?
Clinical trials showed an average weight loss of approximately 14.9% of body weight at the maximum 2.4 mg dose. However, this varied between individuals — some lost more, some less. Weight loss depends on your diet, physical activity, genetics, and how your body responds. Results are not assured, and use our GLP-1 weight loss calculator to see individual projections.
What are the main side effects of Wegovy?
The most common side effects are nausea, diarrhoea, constipation, vomiting, and stomach pain — particularly in the first few weeks as your body adjusts. These often reduce over time. Serious side effects are rare but can include pancreatitis (severe stomach pain) or gallbladder problems. Always report any concerning symptoms to your prescriber immediately.
Can I switch from Mounjaro to Wegovy or vice versa?
Yes, you can switch between medications, but this must be managed by your prescriber. There is no official conversion chart — approximate equivalences exist (e.g. Mounjaro 10 mg ≈ Wegovy 1.7 mg) but individual dosing is personalised. Never switch without medical guidance. ```
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