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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Mounjaro Jabs vs Wegovy — What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription weight loss injections licensed in the UK, but they work in different ways. Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 receptor agonist only. Both are once-weekly injections that may help support weight loss when used alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly, and a prescriber will assess which option is most suitable for your personal circumstances. Use our free GLP-1 weight loss calculator to explore potential outcomes, and check your BMI with our free calculator to understand your starting point.
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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.
How Mounjaro and Wegovy Work — Clinical Trial Evidence
Mounjaro (tirzepatide) activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. This dual action may help regulate appetite more effectively by signalling satiety and reducing food cravings. In the SURMOUNT-1 clinical trial, participants on the maximum 15 mg dose lost an average of 20.9% of their body weight over 72 weeks alongside lifestyle changes.
Wegovy (semaglutide) activates the GLP-1 pathway only. It also supports appetite suppression and may slow gastric emptying. In the STEP-1 clinical trial, participants on the maximum 2.4 mg dose lost an average of 14.9% of body weight over 68 weeks with the same lifestyle approach.
- Mounjaro: dual mechanism may offer greater weight loss potential
- Wegovy: established, single-mechanism option with longer real-world use history
- Both are weekly injections; individual response varies considerably
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.
Dosing, Side Effects, and Getting Them in the UK
Dosing: Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg weekly. Wegovy starts at 0.25 mg and escalates to a maximum of 2.4 mg weekly. Your prescriber will determine the right dose for you based on tolerability and response.
Side effects are similar for both: nausea, diarrhoea, constipation, and stomach pain are common, especially when starting or increasing doses. Both require a prescription and clinical assessment through either NHS specialist weight management services (may involve waiting lists) or private online prescribing. Your GP or prescriber can discuss which option suits your circumstances better, considering your medical history and preferences.
- 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.
Can I switch from Mounjaro to Wegovy or vice versa?
A prescriber can manage a switch between the two medications, though there is no officially established conversion chart. Approximate equivalences exist based on clinical practice (e.g., Mounjaro 10 mg ≈ Wegovy 1.7 mg), but any change must be supervised by your prescriber to ensure safe and effective dosing.
Which weight loss jab is better for me — Mounjaro or Wegovy?
Neither is universally "better" — the right choice depends on your individual health profile, medical history, and how your body responds. Your prescriber will assess your eligibility for each and recommend the most appropriate option. What works well for one person may not suit another.
Are Mounjaro jabs more effective than Wegovy?
Clinical trials suggest Mounjaro may produce slightly greater average weight loss (15–21% vs 14.9% for Wegovy), but individual results vary significantly. Some people respond better to one medication than the other, regardless of average trial data.
How long do I need to use Mounjaro or Wegovy jabs?
Both are typically long-term treatments. If you stop, weight often returns over time. Your prescriber will discuss the expected duration and whether ongoing use is right for you based on your health goals and response.
What's the difference between Mounjaro and Ozempic?
Both contain the same active ingredient families, but Ozempic (at up to 2 mg) is licensed for type 2 diabetes, whereas Mounjaro is a dual GIP+GLP-1 agonist specifically licensed for weight management. Do not use Ozempic for weight loss in the UK — Mounjaro is the licensed weight management option.
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.