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
Is Wegovy Safe?
Yes, Wegovy (semaglutide) is considered safe when prescribed appropriately by a UK healthcare professional, but like all prescription medications, it carries potential side effects that you should understand. Wegovy is a GLP-1 receptor agonist licensed by the MHRA for weight management in UK adults and has undergone rigorous clinical testing. Safety depends on proper medical assessment, correct dosing, monitoring, and following your prescriber's guidance. This guide explains what clinical evidence shows, who should and shouldn't use it, and what to watch for.
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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.
Clinical Safety Evidence and Monitoring
Wegovy's safety profile is based on the STEP clinical trials, which involved thousands of participants over 68 weeks. In these trials, the most common side effects were gastrointestinal — nausea, diarrhoea, vomiting, and constipation — but these typically decreased over time as the body adjusted. Serious adverse events were rare and similar between the medication group and placebo group. The MHRA has approved Wegovy based on this evidence and continues to monitor its safety through pharmacovigilance. Your prescriber will review your medical history, current medications, and health conditions before prescribing. Once on Wegovy, you should have regular follow-up appointments to assess how you're tolerating the injection and monitor for any concerns. This ongoing clinical relationship is a key part of safe use — you're not taking the medication unsupervised.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Who Should Not Take Wegovy and Important Precautions
Wegovy is not suitable if you have a personal or family history of thyroid cancer, medullary thyroid carcinoma, or multiple endocrine neoplasia syndrome type 2. It's also not recommended during pregnancy or breastfeeding. If you have a history of pancreatitis, gallbladder problems, severe gastroparesis, or diabetic retinopathy complications, inform your prescriber — additional caution is needed. Tell your prescriber about all medications you take, as Wegovy may affect how some oral medications are absorbed. If you experience severe, persistent stomach pain radiating to your back, serious allergic reactions, or sudden vision changes, seek immediate medical attention. Your GP or prescriber can assess whether Wegovy is safe for your individual circumstances — this personalised assessment is essential before starting treatment.
- 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 safe compared to Mounjaro?
Both Wegovy (GLP-1 agonist) and Mounjaro (GIP/GLP-1 agonist) are safe when prescribed appropriately, with clinical trial data supporting both. They have similar safety profiles overall, though slightly different side effect patterns. Neither is "safer" — safety depends on individual suitability, assessed by your prescriber. Individual results and tolerability vary.
What are the most common side effects of Wegovy?
The most common side effects are gastrointestinal: nausea, diarrhoea, vomiting, and constipation. These typically occur early in treatment and often improve as your body adjusts over weeks. Less common side effects include headache, fatigue, dizziness, and injection site reactions. Serious side effects are rare but require immediate medical attention if they occur.
Is Wegovy safe to use long-term?
Clinical trial data supports Wegovy use for up to 68 weeks with a good safety profile. Long-term safety beyond this period is still being studied. Your prescriber will review whether continued use is appropriate for you. Weight regain can occur when stopping, so the duration of treatment is an individual decision made with your healthcare provider.
Can I get Wegovy on the NHS in the UK?
Wegovy is available through NHS specialist tier 3 weight management services in some regions, but access varies significantly. Waiting lists can be lengthy. Private prescribing through registered UK pharmacies following an online clinical assessment is also available. Your GP can advise on NHS availability in your area or discuss private options.
How is Wegovy monitored for safety once I start?
You'll have scheduled follow-up appointments with your prescriber to assess how you're tolerating the injection, review side effects, and monitor your health. Blood pressure and other health markers may be checked. Report any concerning symptoms between appointments. This ongoing clinical monitoring is a crucial part of safe treatment with Wegovy.
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.