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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5th Dose Mounjaro Pen — Complete UK Guide
The 5th dose of Mounjaro is typically the 15 mg maintenance dose — the maximum strength available in the UK. By this point in your treatment, you've progressed through the standard dose titration schedule over approximately 20+ weeks. This guide explains what the 5th dose means, what to expect, and how to use your Mounjaro KwikPen safely and effectively as part of your weight management journey.
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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.
Understanding Mounjaro Dose Progression and the 5th Dose
Mounjaro (tirzepatide) uses a structured dose titration schedule to help your body adjust to the medication gradually. Each KwikPen contains 4 individual doses — one injection per week for 4 weeks. The 5th dose marks the beginning of week 21 of treatment.
Standard Mounjaro dose progression:
- Weeks 1–4: 2.5 mg (dose 1)
- Weeks 5–8: 5 mg (dose 2)
- Weeks 9–12: 7.5 mg (dose 3)
- Weeks 13–16: 10 mg (dose 4)
- Weeks 17–20: 12.5 mg (dose 4 progression)
- Week 21+: 15 mg (dose 5 — maximum maintenance)
The 5th dose represents the 15 mg strength, the highest dose available. At this point, you've completed the full titration schedule and reached the maximum therapeutic dose. Clinical trials showed that 15 mg produced the greatest average weight loss, though individual results vary significantly. Your prescriber will confirm whether you should continue at 15 mg or remain at a lower dose based on your progress and tolerance.
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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.
Using Your Mounjaro KwikPen at the 5th Dose and Beyond
Once you reach the 15 mg dose, your KwikPen usage remains the same as previous doses: one injection once weekly, on the same day each week. You can choose any day that suits your routine — consistency matters more than which specific day you select.
Important reminders for safe use: Inject into the stomach (abdomen), upper thigh, or upper arm (with assistance). Rotate your injection site each week to reduce skin irritation. Store unopened pens in the refrigerator (2–8°C) and keep in the original carton. After first use, you can store your pen at room temperature (below 30°C) for up to 30 days. Dispose of the pen 30 days after first injection. Try our free GLP-1 weight loss calculator to see projected outcomes at the 15 mg dose — though remember individual results vary based on diet, activity, and personal factors.
- 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 the 5th dose of Mounjaro always 15 mg?
Yes, the 5th dose is the 15 mg strength — the maximum available dose in the UK. However, your prescriber may recommend staying at a lower dose (12.5 mg or below) if you've achieved good results or experienced side effects. The dose is individualised based on your response and tolerance.
How long do I stay on the 5th dose of Mounjaro?
Once you reach 15 mg, you typically continue at this dose as long as the medication is working well and you're tolerating it. There's no set duration — treatment can continue for months or years depending on your weight management goals and GP or prescriber guidance. Regular reviews are recommended to assess ongoing suitability.
What should I do if I miss my 5th dose injection?
If you miss your 15 mg injection within 4 days of the scheduled time, inject as soon as you remember and resume your normal schedule the following week. If more than 4 days have passed, skip that dose and take your next injection on your normal day. Never take a double dose to make up for a missed injection.
Can I switch between Mounjaro and Wegovy at the 5th dose?
Switching between Mounjaro (tirzepatide) and Wegovy (semaglutide) requires careful prescriber guidance — they work via different mechanisms and have different maximum doses. The approximate equivalent to Mounjaro 15 mg is Wegovy 2.4 mg, but any switch must be managed by your healthcare provider, not done independently.
What if I experience side effects at the 5th dose of Mounjaro?
Common side effects at any dose include nausea, diarrhoea, and stomach discomfort — these often improve over time. If side effects become unbearable, contact your GP or prescriber. They may recommend staying at a lower dose, taking breaks, or adjusting your diet. Serious side effects (severe abdominal pain, allergic reactions) require urgent medical attention.
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.