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 Semaglutide Safe? What NHS Evidence Shows
Yes, semaglutide is considered safe when prescribed appropriately in the UK. Wegovy (semaglutide 2.4mg) is MHRA-approved and licensed for weight management in UK adults. Like all medications, it has potential side effects, but clinical evidence from the STEP trials supports its safety profile when used alongside diet and exercise. The NHS recommends it for eligible adults through specialist weight management services. This guide explains what the evidence shows, who can use it safely, and how to access it 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.
NHS Safety Approval and Clinical Evidence for Semaglutide
Semaglutide (Wegovy) is licensed in the UK by the MHRA specifically for weight management in adults. This means it has undergone rigorous safety and efficacy testing before approval. The medication is a GLP-1 receptor agonist — a class of drugs that work by mimicking a natural hormone involved in appetite regulation.
The STEP-1 clinical trial, involving over 1,900 participants, demonstrated that semaglutide helped people lose an average of approximately 15% of their body weight over 68 weeks. Importantly, this research also tracked safety outcomes: nausea and gastrointestinal side effects were the most common, but most participants were able to continue treatment successfully.
NICE has endorsed semaglutide (as part of the Novo Nordisk GLP-1 class) as an appropriate treatment option for weight management within NHS tier 3 specialist services. The NHS applies strict eligibility criteria to ensure it is prescribed to those most likely to benefit and tolerate it well. Calculate your personal BMI using our free tool above to understand if you might meet initial eligibility thresholds.
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.
Common Side Effects and Who Cannot Use Semaglutide Safely
The most frequently reported side effects are mild to moderate gastrointestinal symptoms: nausea, diarrhoea, constipation, and stomach discomfort. These typically improve over time as the body adjusts. Serious side effects are rare but include severe pancreatitis (signs: severe stomach pain radiating to the back) and gallbladder problems.
Semaglutide is not suitable for you if:
- You are under 18 years old
- You are pregnant, planning pregnancy, or breastfeeding
- You have a personal or family history of medullary thyroid cancer
- You have severe kidney or liver disease
- You have diabetic retinopathy complications
Your GP or prescriber will assess your full medical history before prescribing. Weekly weight loss injections like semaglutide require ongoing monitoring — not a one-off prescription. This ensures your safety and helps optimise your dose if needed.
- 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 safer than other weight loss injections like Mounjaro?
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are MHRA-approved and considered safe when prescribed appropriately. They use different mechanisms: Wegovy is a single GLP-1 agonist, while Mounjaro is a dual GIP/GLP-1 agonist. Individual safety and tolerability vary. Your prescriber will assess which is more appropriate for your health profile.
Can I get semaglutide safely through the NHS?
Yes. NICE has approved semaglutide (as part of GLP-1 therapy) for NHS use through tier 3 specialist weight management services. Access varies by region and availability, with some areas having longer waiting lists. Your GP can refer you to your local specialist service, where clinical assessment determines suitability and safe dosing.
What monitoring is required when taking semaglutide safely?
Regular check-ups with your prescriber are essential. You should report any severe or persistent side effects immediately. Your prescriber will monitor your weight loss, blood pressure, kidney function, and any emerging symptoms. This ongoing care ensures semaglutide remains safe and effective for you personally.
Is it safe to use semaglutide without a prescription from an online pharmacy?
Semaglutide is prescription-only and must only be obtained following a clinical assessment by a UK-licensed prescriber. Some GPhC-registered online pharmacies offer legitimate assessment and prescription services, but you should verify the prescriber is UK-licensed and the pharmacy is registered. Never purchase from unregulated sources.
Can I switch between semaglutide and other weight loss medications safely?
Yes, but only under medical supervision. If you wish to switch from Wegovy to another medication (like Mounjaro or Saxenda), your prescriber will assess your response, side effects, and medical history to determine the safest approach. Never stop or switch medications without clinical guidance. Use our free GLP-1 weight loss calculator to explore projected outcomes with different options. ```
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.