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
How Does Wegovy Work for Weight Loss?
Wegovy is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with 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 food moves through your stomach. Clinical trials showed participants lost an average of around 15% of their body weight — though individual results vary significantly. It's designed to be used alongside a reduced-calorie diet and increased physical activity, not as a standalone treatment. This guide explains how Wegovy works, who can access it, what to expect, and how to get it through NHS or private routes in the UK.
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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.
The Science Behind Wegovy — How Semaglutide Works
Wegovy works by mimicking a natural hormone called GLP-1 (glucagon-like peptide-1) that your gut produces after eating. When you take Wegovy, it activates GLP-1 receptors in your brain, which sends signals that you're full — even if you've eaten less than usual. This may help reduce appetite and food cravings throughout the day.
The medication also slows gastric emptying — the process by which food leaves your stomach and enters your small intestine. This means you feel satisfied for longer after meals, which can make it easier to stick to a reduced-calorie diet without constant hunger.
- Works on the appetite control centres in your brain
- Reduces cravings for sugary and fatty foods
- May improve blood sugar control (helpful if you have type 2 diabetes or prediabetes)
- Slows digestion to increase feelings of fullness
It's important to understand that Wegovy is not insulin and doesn't work like diabetes medications — it's specifically designed for weight management in eligible adults, whether or not they have diabetes.
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 Eligibility, Doses, and Expected Results in the UK
In the UK, Wegovy may be prescribed if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds may apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage.
Wegovy starts at 0.25 mg once weekly, increasing gradually to a maximum of 2.4 mg. In the STEP-1 clinical trial, participants lost approximately 15% of their body weight over 68 weeks — roughly equivalent to 10–15 kg for someone starting at 100 kg. However, results vary widely based on diet, activity, genetics, and consistency with treatment. Use our BMI calculator to check your starting point, and our GLP-1 weight loss calculator can help estimate potential outcomes at different doses.
- 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 quickly will I lose weight on Wegovy?
Weight loss isn't immediate. Most people start seeing changes after 4–8 weeks as they reach therapeutic doses. The gradual dose escalation (0.25 mg to 2.4 mg over 16+ weeks) allows your body to adapt. Average weight loss in clinical trials was around 15% of body weight over 68 weeks. Individual results vary based on diet, exercise, genetics, and adherence.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic (up to 2 mg) is licensed for type 2 diabetes management and is not approved for weight loss in the UK. Wegovy (up to 2.4 mg) is specifically licensed for weight management in eligible adults. Using Ozempic for weight loss would be off-label. Always ask your prescriber which medication is appropriate for your situation.
Can I get Wegovy on the NHS in the UK?
NHS access to Wegovy is limited and varies by region. You would need referral to a specialist tier 3 or tier 4 weight management service through your GP. Many areas have long waiting lists (months to years). Private access via an online consultation with a UK-licensed prescriber is often faster, though there is a cost (typically £150–£300 per month depending on dose).
What are the main side effects of Wegovy?
Common side effects include nausea, diarrhoea, constipation, and vomiting — especially in the first few weeks. Injection site reactions and fatigue can occur. Most side effects ease as your body adjusts. Serious side effects are rare but include severe stomach pain (possible pancreatitis) or gallbladder problems. Always report unusual symptoms to your prescriber.
Is Wegovy safe for long-term use?
Wegovy has been studied for safety over 68 weeks in clinical trials with positive results. However, long-term data beyond this timeframe is still emerging. It's considered safe when prescribed appropriately and monitored by a healthcare professional. Weight regain can occur if you stop the medication, so it's intended as ongoing treatment rather than a short course. Your prescriber will monitor you throughout.
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.