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
Free tracker included with every download this week
What Is Mounjaro's 5th Dose?
Mounjaro's 5th dose marks an important point in your tirzepatide treatment journey. By week 21, most patients have reached the 12.5 mg dose — the fifth injection in the standard UK dosing schedule. Understanding where you are in your treatment plan, what to expect at this stage, and how to access Mounjaro through NHS or private services helps you make informed decisions about your weight management. This guide covers the complete 5th dose picture for UK adults.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Mounjaro 5th Dose in the UK Titration Schedule
Mounjaro's dosing schedule is carefully designed to help your body adjust to tirzepatide. The 5th dose (12.5 mg) arrives at week 21 — typically four months into your treatment. This follows a strict escalation pattern: starting at 2.5 mg, then increasing by 2.5 mg every four weeks until reaching the maximum 15 mg dose at week 21 (6th dose). The 5th dose of 12.5 mg represents a significant therapeutic level for many patients, where weight loss effects are often most noticeable. Each dose uses a single KwikPen injection administered once weekly, always on the same day. The UK MHRA-approved dosing schedule prioritises safety by allowing your body time to adapt to each dose, reducing side effects and improving tolerability. If you experience significant side effects at the 12.5 mg dose, your prescriber may recommend staying at this level longer before progressing to 15 mg.
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.
NHS Access and Private Prescription Routes
In the UK, accessing Mounjaro by your 5th dose depends on your prescribing route. Through NHS specialist tier 3 weight management services, tirzepatide is prescribed following NICE guidance for adults with BMI 30 or above, or BMI 27–29.9 with weight-related conditions like type 2 diabetes or hypertension. However, NHS waiting lists for specialist services vary significantly by region and can extend many months. Private prescribing through registered UK online services offers faster access — your prescriber will assess eligibility and you can begin treatment within days rather than waiting for NHS tier 3 referral. Regardless of route, you must have a clinical assessment confirming Mounjaro is appropriate for your individual health profile before receiving your 5th dose or any dose.
- 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.
What is the 5th dose of Mounjaro in milligrams?
The 5th dose of Mounjaro is 12.5 mg, reached at week 21 (approximately 5 months into treatment). This comes after doses of 2.5 mg, 5 mg, 7.5 mg, and 10 mg, each given for four weeks before escalating.
Can I stay on Mounjaro's 5th dose instead of progressing to 15 mg?
Yes. If 12.5 mg is working well for you and side effects are manageable, your prescriber may recommend continuing at this dose rather than escalating to the maximum 15 mg. Treatment is personalised — there's no requirement to reach 15 mg.
How do I access Mounjaro on the NHS in the UK?
You need a referral to your local tier 3 specialist weight management service through your GP. NICE guidelines support tirzepatide for adults with BMI 30 or above, or BMI 27+ with weight-related health conditions. NHS availability varies by region and waiting times can be lengthy.
What side effects are common at the 5th dose (12.5 mg)?
Side effects at 12.5 mg often include nausea, diarrhoea, constipation, and reduced appetite — most commonly nausea. Side effects typically improve within days to weeks as your body adjusts. Inform your prescriber of any severe or persistent side effects.
How much weight loss can I expect by the 5th dose?
Clinical trials showed varying results, but patients on tirzepatide achieved average weight loss of 15–21% of body weight at higher doses. Results vary significantly — some see noticeable loss by week 21, others see more gradual progress. Use our GLP-1 weight loss calculator to estimate potential outcomes based on your starting weight.
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.