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
Mounjaro Fifth Dose — What You Need to Know
The fifth dose of Mounjaro is 12.5mg, the penultimate step in the standard dose titration schedule. Starting from the initial 2.5mg dose, Mounjaro increases every 4 weeks, with the fifth dose typically reached around week 17–20 of treatment. This guide explains the dosing timeline, what to expect at this stage, and how to access Mounjaro in the UK through both NHS specialist services and private prescription routes. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
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 Dose Titration Schedule & the Fifth Dose
Mounjaro follows a structured dose titration schedule, with doses increasing every 4 weeks to allow your body to adjust and minimise side effects. The schedule progresses: 2.5mg (weeks 1–4) → 5mg (weeks 5–8) → 7.5mg (weeks 9–12) → 10mg (weeks 13–16) → 12.5mg (weeks 17–20, the fifth dose) → 15mg (week 21 onwards, maximum dose).
At the fifth dose, most patients have already experienced initial weight loss and gastrointestinal side effects typically begin to stabilise. The 12.5mg dose is a substantial step — falling between the 10mg dose and the maximum 15mg tirzepatide. Some patients remain on 12.5mg if this dose delivers the desired weight loss and is well tolerated, whilst others continue to the 15mg maximum after a further 4-week period. Your prescriber will assess your progress and tolerance before escalating further.
It's important to note that dose increases only occur if you've remained on the previous dose for at least 4 weeks — skipping or accelerating doses is not recommended as it increases the risk of gastrointestinal upset and may be medically inadvisable.
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.
Accessing Mounjaro in the UK — Private and NHS Routes
Private prescription route: Mounjaro is available through UK-licensed online prescribers following a confidential clinical assessment. Private prescriptions are typically processed within 24–48 hours, with medication dispatched by registered pharmacies. Costs for the fifth dose (12.5mg KwikPen) range from approximately £180–£250 per pen, depending on the provider and any volume discounts applied. This route offers faster access without NHS waiting lists.
NHS route: NICE has approved tirzepatide for NHS use within specialist tier 3/4 weight management services. However, NHS availability is limited and regional variation is significant — some areas have lengthy waiting lists of several months to years. You would need referral from your GP to a specialist weight management centre, where a multidisciplinary team assesses eligibility and prescribes if appropriate. NHS treatment is free at point of use but access is not assured immediately.
Track your weight loss journey using our free progress tracker to monitor results alongside whichever route you choose.
- 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 exact timing of the fifth Mounjaro dose?
The fifth dose (12.5mg) is typically administered around week 17–20 of treatment, assuming you've remained on the previous dose for a full 4-week interval. If dose escalation is delayed for any reason (side effects, prescriber review), the timeline adjusts accordingly. Always follow your prescriber's specific guidance on timing.
Can I skip the fifth dose and stay on 10mg indefinitely?
Yes. There's no requirement to increase beyond any dose. Many patients achieve satisfactory weight loss on 10mg and choose to remain there long-term if side effects are manageable and outcomes meet their goals. Your prescriber will discuss your individual response at each review.
How much does Mounjaro 12.5mg cost privately in the UK?
Private Mounjaro 12.5mg KwikPens typically cost between £180–£250 per pen (4-week supply) depending on the provider and current pricing. Some providers offer bundle discounts for multiple pens. Prices vary, so it's worth comparing online prescribing services that are registered with the GPhC.
What's the difference between Mounjaro and Wegovy at higher doses?
Mounjaro is a dual GIP and GLP-1 agonist with a maximum dose of 15mg weekly, whilst Wegovy is a GLP-1-only agonist with a maximum of 2.4mg weekly. At the fifth dose, Mounjaro 12.5mg is a higher absolute milligram dose, though direct clinical equivalence between the two medications differs and both work differently in the body.
Will I experience side effects at the fifth dose?
Side effects vary individually. Many patients find gastrointestinal side effects (nausea, constipation, diarrhoea) begin to ease by week 17–20 as the body adapts. However, some people experience new or worsening side effects with dose increases. Report any concerns to your prescriber immediately, who may adjust the dose or explore management strategies.
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.