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
How Do I Take Mounjaro in the UK?
Mounjaro (tirzepatide) is a prescription-only, once-weekly injection used for weight management in the UK. You administer it yourself as a subcutaneous injection using a pre-filled KwikPen device. Understanding the correct dosing schedule, injection technique, and storage is essential for safe and effective use. This guide explains how to take Mounjaro following NHS and MHRA guidance, covering dose titration, practical administration, and what to expect during treatment.
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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 Dosing Schedule and Titration
Mounjaro is administered as a once-weekly injection using a pre-filled KwikPen. Treatment follows a structured dose titration schedule, meaning your dose increases gradually over several weeks to allow your body to adjust and minimise side effects.
- Weeks 1–4: 2.5 mg (starting dose)
- Weeks 5–8: 5 mg (first escalation)
- Weeks 9–12: 7.5 mg
- Weeks 13–16: 10 mg
- Weeks 17–20: 12.5 mg
- Week 21+: 15 mg (maximum dose)
You remain on each dose for a minimum of 4 weeks before increasing. Your prescriber may adjust this schedule based on your individual response and tolerance. Each KwikPen contains 4 doses (a 4-week supply), so you will receive a new pen every month during titration.
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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.
Injection Technique and Storage in UK Practice
Inject Mounjaro subcutaneously (under the skin) once weekly on the same day each week. You can inject into your stomach, upper thigh, or upper arm — rotate injection sites each week to reduce irritation. Store unopened pens in your fridge at 2–8°C; do not freeze. After first use, you can store the pen at room temperature (below 30°C) for up to 30 days, then discard. Each KwikPen is pre-filled and ready to use — no mixing or measuring required. If you miss a dose, inject within 4 days of the scheduled date and continue your normal weekly schedule.
- 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 starting dose of Mounjaro in the UK?
The standard UK starting dose is 2.5 mg once weekly for 4 weeks. This allows your body to adapt and reduces nausea and other side effects. Your prescriber will increase the dose gradually every 4 weeks until you reach an effective maintenance dose, typically 5–15 mg weekly.
Can I inject Mounjaro myself at home?
Yes. Mounjaro is supplied as a pre-filled KwikPen specifically designed for self-injection at home. Your prescriber or practice nurse will show you the correct injection technique before you start. If you are unsure at any point, contact your GP or prescribing clinic for guidance.
How long does a Mounjaro KwikPen last?
Each KwikPen contains 4 weekly doses and lasts 4 weeks. You will receive a new pen every month. Always check the expiry date on the pen before use. Store unopened pens in the fridge; once opened, use within 30 days at room temperature.
What happens if I miss a weekly injection?
If you miss a dose within 4 days of your scheduled injection day, take it as soon as you remember and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and inject on your normal scheduled day. Never take a double dose to make up for a missed one.
Is Mounjaro available on the NHS in the UK?
Mounjaro is NICE-approved and available through NHS specialist tier 3 weight management services, but availability and waiting times vary significantly by region. Many people access Mounjaro privately through a GPhC-registered pharmacy following an online clinical assessment with a UK-licensed prescriber, which may offer faster access.
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.