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 Semaglutide Safe โ How Wegovy Compares to Mounjaro
Yes, semaglutide is safe when prescribed and monitored by a healthcare professional, but like all medications, it carries specific side effects and isn't suitable for everyone. This guide compares the safety profile of Wegovy (semaglutide 2.4mg) with Mounjaro (tirzepatide), using clinical trial data and NHS guidance. Both are prescription-only weight loss injections approved by the MHRA for use in the UK. Understanding the differences helps you and your prescriber decide which might be appropriate for your individual circumstances.
10,000+ calculations today ยท NHS-aligned thresholds ยท 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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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.
Semaglutide Safety and Clinical Trial Evidence
Wegovy (semaglutide) is a GLP-1 receptor agonist that works by activating one hormone pathway in the gut. Clinical trials (the STEP programme) involving thousands of participants showed it to be effective and generally well-tolerated. Common side effects include nausea, diarrhoea, constipation, and vomiting โ typically most pronounced during dose escalation and often improving over time.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways. The SURMOUNT clinical trials reported a similar side effect profile to semaglutide but with potentially higher rates of nausea and gastrointestinal effects during the dose escalation phase. Both medications carry rare but serious risks including pancreatitis, gallbladder problems, and diabetic retinopathy complications in people with existing diabetes.
Both medications are subject to MHRA monitoring (Black Triangle โผ status), meaning safety data is actively reviewed. Neither is suitable during pregnancy, and both may affect the absorption of oral contraceptives.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care โ 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 โ 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 โ completely free.
Which Is Safer โ Individual Suitability Matters Most
Safety is not about which medication is "better" overall โ it's about which is suitable for you. A prescriber will assess your medical history, current medications, and any existing conditions to determine whether semaglutide, tirzepatide, or neither is appropriate. Some people tolerate one medication better than the other; individual responses vary significantly.
Try our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and use the BMI calculator to understand your current health context. Both tools help you ask informed questions when discussing weight management options with your GP or prescriber. All prescription weight loss medications require a clinical assessment โ there is no "safest" choice without personalised medical evaluation.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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 semaglutide safer than tirzepatide?
Both have comparable safety profiles based on clinical trials. Semaglutide (Wegovy) activates one hormone pathway (GLP-1), while tirzepatide (Mounjaro) activates two (GIP and GLP-1). Side effects are similar, but individual tolerance varies. Your prescriber will assess which is safer for your specific health circumstances.
What are the most common side effects of semaglutide?
Nausea, diarrhoea, constipation, and vomiting are very common, especially during dose escalation. These typically improve over weeks as your body adjusts. Other common effects include indigestion, headache, fatigue, and injection site reactions. Report persistent or severe symptoms to your prescriber.
Can I take semaglutide if I have diabetes?
Semaglutide can be used in people with type 2 diabetes, but requires careful prescriber monitoring because it lowers blood sugar. If you take diabetes medications (especially insulin or sulphonylureas), your prescriber may need to adjust doses. This is managed through clinical assessment and follow-up appointments.
Is semaglutide the same as Ozempic?
Both contain semaglutide, but Ozempic (up to 2mg) is licensed for type 2 diabetes, while Wegovy (2.4mg) is licensed specifically for weight management in the UK. Ozempic is not licensed for weight loss in the UK โ only Wegovy is the approved weight management version.
How is semaglutide safety monitored in the UK?
Semaglutide has Black Triangle (โผ) status with the MHRA, meaning safety is actively monitored. Your prescriber will arrange follow-up appointments to check how you're tolerating the medication, monitor side effects, and assess weight loss progress. Always report new or concerning symptoms to your healthcare provider.
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.