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 Weight Loss Medication: How It Works
Wegovy is a prescription-only weekly weight loss injection licensed in the UK for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. The active ingredient is semaglutide, a GLP-1 receptor agonist that helps regulate appetite and supports feeling fuller after smaller meals. Wegovy is distinct from Ozempic, which is the diabetes version of semaglutide and not licensed for weight management. This guide explains how Wegovy works, compares it factually to Mounjaro (the alternative weekly weight loss injection available in the UK), and explains how to access treatment through NHS specialist services or private prescribing.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 vs Mounjaro: Mechanism and Clinical Evidence
Wegovy (semaglutide) is a single GLP-1 receptor agonist — it activates one hormone pathway involved in appetite regulation and blood sugar control. In the STEP-1 clinical trial, participants taking Wegovy 2.4 mg (the maximum dose) lost an average of approximately 14.9% of their body weight over 68 weeks, alongside a reduced-calorie diet and increased physical activity.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways. In the SURMOUNT-1 clinical trial, participants on Mounjaro 15 mg lost an average of approximately 20.9% of their body weight over 72 weeks under similar lifestyle conditions.
- Both require weekly injections and are prescription-only
- Both are licensed for the same BMI eligibility criteria in the UK
- Trial data shows different average weight loss percentages, but individual results vary significantly
- Both work best when combined with dietary changes and increased physical activity
The choice between them depends on individual suitability, assessed by a prescriber following a clinical consultation.
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.
Wegovy Doses, Side Effects, and Access in the UK
Wegovy is dosed from 0.25 mg weekly, escalating gradually every 4 weeks to a maximum of 2.4 mg. Common side effects include nausea, diarrhoea, constipation, and stomach discomfort — most people find these improve over time. Serious side effects are rare but can include pancreatitis symptoms (severe stomach pain) or gallbladder issues.
Access in the UK: Wegovy is available through NHS specialist weight management services (Tier 3) following a GP referral, though availability and waiting times vary significantly by region. It is also available through private online prescribing following a clinical assessment with a UK-licensed prescriber. Use our GLP-1 weight loss calculator to estimate potential weight loss at different doses, and our BMI calculator to check if you meet eligibility thresholds.
You may be eligible for Wegovy if you have a BMI of 30 or above, or 27 or above with weight-related conditions such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may be eligible at lower BMI thresholds due to higher health risks at these levels.
Wegovy is not suitable if you are under 18, pregnant, breastfeeding, or have a personal or family history of medullary thyroid cancer or multiple endocrine neoplasia syndrome type 2 (MEN 2). A prescriber will assess your individual health history and medical conditions to determine suitability.
- 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?
No. Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (doses up to 2 mg) and is not licensed for weight loss in the UK. Wegovy is the weight management version with doses up to 2.4 mg. Using Ozempic for weight loss is off-label use in the UK. Always ensure you receive the licensed Wegovy product if prescribed for weight management.
Can I switch from Mounjaro to Wegovy?
Yes, but only under prescriber guidance. While approximate dose equivalences exist (Mounjaro 10 mg ≈ Wegovy 1.7 mg), there is no official established conversion chart. Any switch between medications must be managed by your prescriber, who will assess your individual response and adjust accordingly.
How much weight can I expect to lose on Wegovy?
Clinical trials showed average weight loss of approximately 14.9% of body weight on Wegovy 2.4 mg over 68 weeks. However, individual results vary significantly — some people lose more, some less. Weight loss depends on your starting weight, diet adherence, physical activity, genetics, and overall health. A prescriber can give you a more personalised indication based on your circumstances.
Is Wegovy available on the NHS in the UK?
Yes, Wegovy is licensed for NHS prescription through specialist weight management services (Tier 3). However, availability varies significantly by region and NHS integrated care board. Waiting times can be months to years in many areas. Private prescribing through online consultations offers faster access if you meet clinical eligibility criteria.
What happens when I stop taking Wegovy?
Weight regain is common after stopping Wegovy if diet and exercise habits do not remain changed. Many people regain weight within months. This is why Wegovy is typically prescribed as a longer-term treatment, often for 12 months or more, combined with sustained lifestyle changes. Your prescriber will discuss how long to continue treatment based on your progress and health goals.
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.