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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Is Wegovy Safe For Weight Loss?
Wegovy (semaglutide) is a prescription-only weekly weight loss injection licensed in the UK for adults with obesity or overweight with health conditions. Like all medications, Wegovy has both benefits and potential side effects that you should understand before starting. This guide compares Wegovy's safety profile with Mounjaro, explains what clinical trials showed, and helps you understand whether a semaglutide weight loss injection might be suitable for you. Always discuss any concerns with your GP or prescriber before beginning treatment.
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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.
Wegovy Safety Profile — Clinical Evidence and Side Effects
Wegovy (semaglutide) has been extensively studied in clinical trials, most notably the STEP programme. Clinical trial data showed Wegovy to be generally well-tolerated, with the most common side effects being gastrointestinal in nature. Most users experience nausea, diarrhoea, constipation, or stomach discomfort, particularly when starting or increasing doses. These effects typically reduce over time as the body adjusts.
The main safety consideration is that Wegovy is not suitable for certain groups: pregnant or breastfeeding women, people under 18, or those with a personal or family history of medullary thyroid cancer or multiple endocrine neoplasia type 2 (MEN2). Serious side effects are rare but can include pancreatitis (severe stomach pain), gallbladder problems, and changes in vision. Because Wegovy affects how quickly food leaves your stomach, it may also reduce absorption of some oral medications, including oral contraceptives — women taking these should use an additional barrier method for 4 weeks after starting and after each dose increase.
Your prescriber will assess your full medical history to determine if Wegovy is safe for you personally. This is why a clinical assessment is mandatory before receiving a prescription.
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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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Wegovy vs Mounjaro — Safety and Mechanism Comparison
Both Wegovy and Mounjaro are licensed for weight management in the UK, but they work differently. Wegovy is a GLP-1 receptor agonist only, while Mounjaro is a dual GIP and GLP-1 receptor agonist. This difference in mechanism means Mounjaro activates two hormone pathways rather than one, which may affect how well each medication works for different individuals — though clinical trial data shows both are effective.
Safety profiles are broadly similar: both can cause nausea, diarrhoea, constipation, and injection site reactions. In clinical trials, Wegovy (STEP trial) showed average weight loss of approximately 15% of body weight, whilst Mounjaro (SURMOUNT trial) showed approximately 15–21% — but individual results vary significantly. Which medication is suitable for you depends on your personal health circumstances, not on one being universally "safer" than the other. Your prescriber will recommend the medication most appropriate for your situation following a clinical assessment.
- 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 are the most common side effects of Wegovy?
The most common side effects are nausea, diarrhoea, vomiting, constipation, and stomach pain — affecting more than 1 in 10 users in trials. These are usually mild to moderate and tend to improve as your body adjusts. Nausea is most common when starting or increasing doses. Injection site reactions (redness, bruising) are also common. Serious side effects are rare but include pancreatitis and gallbladder problems.
Is Wegovy safer than Mounjaro?
Both medications have similar safety profiles with comparable side effect rates. Neither is universally "safer" — suitability depends on your individual health circumstances. Wegovy is a GLP-1 agonist; Mounjaro is a dual GIP+GLP-1 agonist. Clinical trials show both are well-tolerated. Your prescriber will recommend whichever is more appropriate for you following a clinical assessment.
Who should not take Wegovy?
Wegovy is not suitable for people who are pregnant, breastfeeding, under 18, or have a personal or family history of medullary thyroid cancer or MEN2 syndrome. It may not be appropriate if you have severe gastroparesis, recent pancreatitis, or certain other conditions. Your GP or prescriber will assess your full medical history to confirm suitability.
Can I take Wegovy if I'm on other medications?
Wegovy may affect absorption of oral medications. If you take oral contraceptives, you should add a barrier method or switch to non-oral contraception for 4 weeks after starting and after dose increases. Always inform your prescriber of all medications you take — they can advise whether any adjustments are needed.
How does the weekly weight loss injection differ from daily injections?
Wegovy is a once-weekly injection (semaglutide 2.4 mg), making it more convenient than daily alternatives like Saxenda (liraglutide). Clinical trials showed Wegovy effective for weight management when used alongside a reduced-calorie diet and increased physical activity. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses.
Ready to take control of your weight loss journey?
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