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
I'm Having Side Effects — What You Need to Know
If you're experiencing side effects while taking Wegovy (semaglutide) for weight management, you're not alone — nausea, diarrhoea, and stomach discomfort are very common, especially when starting or increasing your dose. Most side effects settle within a few weeks as your body adjusts, though some may persist. This UK health guide explains what's normal, what requires GP attention, and how to manage symptoms alongside your weight loss journey. Always speak to your prescriber if side effects concern you or significantly impact your daily life.
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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.
Common Wegovy Side Effects and Timeline
Very common side effects (affecting more than 1 in 10 people) include nausea, diarrhoea, vomiting, constipation, and stomach pain. These typically occur when starting treatment or after dose increases, often improving within 2–4 weeks as your body adjusts to the medication.
Nausea management tips: Eat smaller, lighter meals; avoid greasy or heavy foods; stay hydrated; take your injection on a day when you can rest if needed. Diarrhoea or constipation: Increase fibre and water intake gradually; both usually resolve as treatment continues. Stomach pain: If mild and manageable, it often improves with time and dietary adjustments.
Common but less frequent side effects include indigestion, headache, fatigue, dizziness, and injection site reactions (redness or bruising at the injection point). Use our free BMI calculator to track your baseline health metrics alongside your weight loss progress.
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.
When to Contact Your GP — Serious Side Effects
Contact your GP or seek urgent medical attention if you experience: severe stomach pain spreading to your back (possible pancreatitis), persistent vomiting preventing food or fluid intake, signs of a serious allergic reaction (swelling of lips, tongue, or throat), or unexplained changes in vision. These are rare but require immediate assessment.
Wegovy is prescription-only and requires ongoing clinical monitoring. Your prescriber can adjust your dose, suggest additional support, or explore alternatives if side effects are intolerable. Don't stop taking Wegovy abruptly without medical advice — discuss any concerns at your next appointment. Track your weight loss and symptom patterns using our free progress tracker to share helpful information with your healthcare team.
- 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 long do Wegovy side effects last?
Most side effects improve within 2–4 weeks of starting or increasing your dose as your body adjusts. Nausea and diarrhoea are most common initially. However, some people experience persistent mild symptoms throughout treatment. If side effects don't improve or worsen, contact your prescriber for personalised advice.
Can I reduce my Wegovy dose if side effects are severe?
Yes — your prescriber can lower your dose or slow the escalation schedule to help side effects settle. Never adjust your dose yourself without medical guidance. Contact your prescriber to discuss options; dose adjustments are a normal part of treatment management.
Is it normal to feel very tired on Wegovy?
Fatigue is a common side effect, especially when starting treatment or increasing doses. It often improves within a few weeks. Ensure you're eating adequate calories and nutrients, staying hydrated, and getting enough sleep. If fatigue is severe or persistent, discuss it with your GP.
Will side effects affect my weight loss results?
Side effects don't prevent weight loss — clinical trials showed average weight loss of around 15% body weight with Wegovy. Side effects like nausea may actually reduce appetite initially. However, managing side effects well helps you stick with treatment long-term, which supports sustained weight loss.
What's the difference between Wegovy and Ozempic side effects?
Both contain semaglutide but Wegovy is licensed for weight management (up to 2.4mg) whilst Ozempic is for type 2 diabetes (up to 2mg). Wegovy's higher doses may cause more pronounced side effects. Side effect profiles are similar, but Wegovy is the NHS-approved weight management option in the UK.
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.