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 Every 5 Days vs Wegovy: Understanding the Differences
Mounjaro is designed as a once-weekly injection, not every 5 days, whereas Wegovy is also once-weekly. This guide clarifies the correct dosing schedules for both UK-licensed medications, explains how they work differently, and helps you understand what prescribers consider when recommending one over the other. Both are prescription-only and require clinical assessment before use.
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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.
How Mounjaro and Wegovy Dosing Schedules Work
Mounjaro (tirzepatide) is administered as a once-weekly injection using a pre-filled KwikPen device. The dosing schedule begins at 2.5 mg for weeks 1–4, then escalates by 2.5 mg increments every 4 weeks up to a maximum of 15 mg per week. Each KwikPen contains 4 doses, providing a 4-week supply. It is not designed for every 5-day dosing.
Wegovy (semaglutide) follows a similar once-weekly schedule, starting at 0.25 mg for weeks 1–4, then escalating to 0.5 mg, 1 mg, 1.7 mg, and finally 2.4 mg as the maximum dose. Like Mounjaro, it is a once-weekly injection, not every 5 days. Both medications rely on consistent weekly intervals for optimal effectiveness.
If you have missed a dose or are considering adjusting your injection timing, always consult your prescriber. They may advise taking the next dose within 3–4 days, but changing the regular schedule is not recommended without medical guidance.
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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.
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Mechanism Differences and Clinical Trial Data
The key difference between these medications is their mechanism of action. Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously to regulate appetite and blood sugar. Wegovy is a GLP-1 receptor agonist only, activating a single pathway. In clinical trials (SURMOUNT-1 for Mounjaro, STEP-1 for Wegovy), Mounjaro showed average weight loss of approximately 15–21% of body weight, while Wegovy showed approximately 15% at the maximum 2.4 mg dose. Individual results vary significantly. Both medications are used alongside a reduced-calorie diet and increased physical activity, and your prescriber will assess which is more suitable for your individual health circumstances and medical history.
- 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 ever injected every 5 days instead of weekly?
No. Mounjaro is exclusively a once-weekly injection. There is no approved every 5-day dosing schedule in the UK. If you've missed a dose, your prescriber may advise taking it within 3–4 days, but the standard interval is 7 days. Always follow your prescriber's specific guidance.
How do Mounjaro and Wegovy differ in how they work?
Mounjaro is a dual GIP and GLP-1 agonist, activating two hormone pathways. Wegovy is a GLP-1 agonist only. This dual mechanism in Mounjaro may contribute to slightly higher average weight loss in clinical trials, though individual responses vary considerably.
Which medication causes more side effects — Mounjaro or Wegovy?
Both medications have similar common side effects including nausea, diarrhoea, and constipation. The frequency and severity vary between individuals. Your prescriber will discuss side effect profiles during your clinical assessment and choose the most suitable option for you.
Can my GP prescribe Mounjaro or Wegovy on the NHS in the UK?
Prescription access via the NHS is typically through specialist tier 3 weight management services, not routine GP prescribing. Availability and waiting times vary significantly by region. Private prescribing is also available through UK-licensed online prescribers.
What should I do if I want to know which medication is right for me?
Use our free BMI calculator and GLP-1 weight loss calculator on this page to understand your starting point, then discuss your results with your GP or a licensed prescriber. They will assess your eligibility, medical history, and individual circumstances to recommend the most suitable medication.
Ready to take control of your weight loss journey?
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