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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What Is Mounjaro's 5th Dose Syringe?
Mounjaro's 5th dose syringe contains 15 mg of tirzepatide — the maximum licensed dose in the UK. This dose is reached after a gradual 16-week titration schedule, where each dose is increased every 4 weeks. The 15 mg dose is the highest strength available and is typically the maintenance dose for ongoing weight management. Not all patients require the maximum dose; many achieve their weight loss goals at lower doses like 10 mg or 12.5 mg. Your prescriber will assess your individual response and determine the most appropriate maintenance dose for you.
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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
Mounjaro dosing follows a structured escalation schedule designed to allow your body to adjust to the medication and minimise side effects. The 5th dose, containing 15 mg tirzepatide, is reached at week 21 onwards — meaning 16 weeks of gradual increases. Here's the progression:
- Weeks 1–4: 2.5 mg (starting dose)
- Weeks 5–8: 5 mg (first escalation)
- Weeks 9–12: 7.5 mg (second escalation)
- Weeks 13–16: 10 mg (third escalation)
- Weeks 17–20: 12.5 mg (fourth escalation)
- Week 21+: 15 mg (fifth dose — maximum)
Each dose is a once-weekly injection via the Mounjaro KwikPen device. Your prescriber may keep you at a lower dose if you're experiencing side effects or have achieved satisfactory weight loss results — reaching 15 mg is not mandatory. Some patients remain on 10 mg or 12.5 mg as their maintenance dose, which is clinically appropriate.
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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.
Reaching the 5th Dose and Clinical Considerations
To reach the 5th dose (15 mg), you must complete the full titration schedule, spending at least 4 weeks at each dose level. If you experience persistent nausea, vomiting, or other side effects, your prescriber may extend the time at a particular dose or decide to maintain you at a lower strength. The 15 mg dose is not suitable for everyone — some patients achieve excellent weight loss results at 10 mg and prefer to avoid higher doses due to side effect concerns. Your GP or prescriber will monitor your progress and adjust your dose based on your individual response. Using our free GLP-1 weight loss calculator can help you understand projected outcomes at different doses.
- 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 15 mg Mounjaro dose the maximum available in the UK?
Yes. The 15 mg dose is the maximum licensed strength of tirzepatide available in the UK. This is the 5th dose in the titration schedule. However, not all patients need to reach this dose — many achieve satisfactory weight loss and weight management at 10 mg, 12.5 mg, or lower doses.
How long does it take to reach Mounjaro's 5th dose?
It takes a minimum of 16 weeks (approximately 4 months) to reach the 5th dose of 15 mg. You spend at least 4 weeks on each dose level before escalating. If your prescriber extends any dose period due to side effects, it may take longer.
Can I skip doses and go straight to 15 mg Mounjaro?
No. The Mounjaro dosing schedule is designed to allow gradual titration for safety and tolerability. Starting at a higher dose increases the risk of severe nausea and gastrointestinal side effects. The stepped approach helps your body adapt to the medication.
What if I experience side effects when reaching the 5th dose?
If you develop significant side effects at 15 mg, contact your prescriber immediately. You may remain on a lower dose permanently — many patients manage weight effectively at 10 mg or 12.5 mg. Your prescriber can assess whether dose reduction is appropriate for you.
Is the 15 mg Mounjaro dose vs Wegovy dose equivalent?
Approximate equivalence suggests 15 mg Mounjaro is roughly equivalent to 2.4 mg Wegovy (semaglutide's maximum dose). However, these are different medications with different mechanisms — Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is GLP-1 only. Direct comparisons should always be made with your prescriber.
Ready to take control of your weight loss journey?
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