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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What Are the Other Names for Semaglutide?
Semaglutide is sold under different brand names depending on its approved use and dose. The most common semaglutide brand names in the UK are Wegovy (for weight management) and Ozempic (for type 2 diabetes). However, when it comes to weight loss injections specifically, it's important to understand the distinction between semaglutide-based medications and newer alternatives like Mounjaro. This guide explains the different names, what they mean, and how they compare for UK adults considering weight management treatment.
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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.
Semaglutide Brand Names and Mechanism Differences
Semaglutide is the active ingredient in two main UK-licensed products:
- Wegovy — semaglutide 2.4 mg, approved specifically for weight management in adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions
- Ozempic — semaglutide up to 2 mg, approved for type 2 diabetes management (not licensed for weight loss in the UK)
Semaglutide is a GLP-1 receptor agonist — it activates one natural hormone pathway to reduce appetite and support feeling fuller after meals. In clinical trials (the STEP-1 trial), Wegovy helped participants lose approximately 14.9% of body weight on average over 68 weeks, alongside a reduced-calorie diet and increased physical activity. However, a newer medication — Mounjaro (tirzepatide) — uses a different mechanism. Mounjaro is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways rather than one. Clinical trial data (SURMOUNT-1) showed participants on Mounjaro lost an average of 15–20.9% of body weight depending on dose. Individual results vary significantly.
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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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Choosing Between Semaglutide-Based and Dual-Action Options
Both Wegovy (semaglutide) and Mounjaro are prescription-only medicines requiring a clinical assessment from a UK-licensed prescriber. Your prescriber will consider your personal health, medical history, BMI, and any weight-related conditions to decide which is most suitable for you. Neither medication is "better" — they work through different mechanisms, and individual response varies. Wegovy has longer-established safety data (semaglutide has been used for diabetes for longer), while Mounjaro is newer but shows strong clinical results. Both are used alongside lifestyle changes — dietary modifications and increased physical activity are essential for best outcomes. Use our free GLP-1 weight loss calculator to understand potential outcomes at different doses, and discuss eligibility with your GP or a licensed prescriber.
- 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 semaglutide the same as Wegovy?
Semaglutide is the active ingredient in Wegovy, but the names refer to different things. Semaglutide is the chemical name; Wegovy is the brand name for semaglutide specifically licensed for weight management at 2.4 mg dose in the UK. Ozempic is also semaglutide but at a lower dose and approved for diabetes, not weight loss.
What's the difference between a GLP-1 and a GIP/GLP-1 receptor agonist?
GLP-1 receptor agonists (like Wegovy) activate one hormone pathway to reduce appetite. Dual GIP/GLP-1 receptor agonists (like Mounjaro) activate two pathways. The dual action may offer additional benefits, though individual results vary. Your prescriber will advise which is appropriate for you.
Is Mounjaro better than Wegovy for weight loss?
Clinical trials show both medications support significant weight loss — Wegovy approximately 14.9% and Mounjaro 15–20.9% on average. "Better" depends on individual factors including your health, medical history, and how your body responds. Only a prescriber can assess which is suitable for you.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between weight loss medications must be managed by your prescriber. While approximate dose equivalences exist, there is no official established conversion chart. Your prescriber will guide any switch based on your individual response and health.
Is semaglutide available on the NHS for weight loss?
Access to semaglutide (Wegovy) on the NHS for weight loss is limited and varies by region. It may be available through specialist tier 3 weight management services following referral from your GP, though waiting lists can be lengthy. Private prescription through a UK-licensed prescriber is also an option.
Ready to take control of your weight loss journey?
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