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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How Often Is Mounjaro Injection Compared to Wegovy?
Mounjaro is a once-weekly weight loss injection, meaning you inject yourself once every 7 days using a pre-filled KwikPen device. This differs from some other weight loss injections available in the UK. Wegovy, another popular weight management option, is also a once-weekly injection. Understanding the injection frequency and how these two prescription medications work can help you and your GP decide which might be more suitable for your individual health needs following a clinical assessment.
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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.
Mounjaro vs Wegovy — Injection Frequency and Mechanism
Both Mounjaro and Wegovy are once-weekly injections, so the injection frequency is identical. The key difference lies in how they work. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways to help regulate appetite and food cravings. Wegovy (semaglutide) is a single GLP-1 receptor agonist, working through one pathway.
In clinical trials, Mounjaro showed average weight loss of around 15–21% of body weight, whilst Wegovy achieved approximately 14.9% at its maximum dose. However, individual results vary significantly. Both require dose escalation over several weeks: Mounjaro starts at 2.5 mg weekly and increases to a maximum of 15 mg, whilst Wegovy starts at 0.25 mg and escalates to 2.4 mg. Each medication is a weekly weight loss injection dispensed as a KwikPen, making them equally convenient in terms of injection frequency.
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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.
Choosing Between Them — Individual Suitability
The choice between Mounjaro and Wegovy depends on your individual health profile, medical history, and how you respond to treatment — this is why a clinical assessment from a UK-licensed prescriber is essential. Some people respond better to the dual-action mechanism of Mounjaro, whilst others find Wegovy equally effective. Your GP or a prescriber will review your weight loss goals, existing health conditions (such as type 2 diabetes or prediabetes), current medications, and any contraindications.
Both medications are available through NHS specialist weight management services (tier 3) or via private online prescribing with a UK-licensed prescriber. Once prescribed, you can track your progress using our free progress tracker to monitor weight changes and how you feel on treatment. Individual response varies, so regular follow-up and dose adjustment are important parts of your treatment plan.
- 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 Mounjaro injected weekly like Wegovy?
Yes, both are once-weekly injections. You use a pre-filled KwikPen to inject yourself once every 7 days into your stomach, thigh, or upper arm. Neither requires daily injections, making them equally convenient in terms of frequency.
Which weight loss injection is stronger — Mounjaro or Wegovy?
Mounjaro uses a dual mechanism (GIP + GLP-1), whilst Wegovy is a single GLP-1 agonist. Clinical trials suggest Mounjaro achieved slightly higher average weight loss (15–21% vs 14.9%), but individual results vary significantly. A prescriber will assess which is more suitable for you.
How long does a Mounjaro KwikPen last?
Each pre-filled KwikPen contains 4 doses (4 weeks supply). You receive a new pen weekly at your current dose. As you escalate doses, you may receive pens containing higher doses every 4 weeks during titration.
Can I switch from Wegovy to Mounjaro on the NHS?
This depends on your NHS trust and specialist weight management service availability. Regional variation in UK NHS access is significant. Discuss any medication change with your prescriber — switching is sometimes possible but requires clinical justification and reassessment.
Do I need to store Mounjaro differently because of weekly injections?
Unopened pens are stored in the fridge (2–8°C) until use. After first injection, you can keep your pen at room temperature (below 30°C) for up to 30 days. Discard the pen after 30 days whether fully used or not.
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.