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 — Complete Injection Guide
Mounjaro (tirzepatide) is a prescription-only, once-weekly injection for weight management in UK adults. You inject it yourself using a pre-filled KwikPen device. This guide explains the correct technique, injection sites, storage requirements, and what to expect at each dose level during your treatment journey. Always follow your prescriber's instructions and speak to your GP if you have any concerns.
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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.
Mounjaro Injection Technique and Sites
Mounjaro comes as a pre-filled KwikPen that you inject once a week, always on the same day. Each pen contains four weekly doses. You inject under the skin (subcutaneously) into one of three areas: your stomach (abdomen), upper thigh, or upper arm — though the arm requires someone to help you. Rotate your injection site each week to avoid skin irritation or lumps forming in one area. Clean the injection site with an alcohol wipe before injecting. You do not need to use ice or numb the area first. The needle is very thin and most people experience minimal discomfort. After injecting, you can massage the area gently if you wish — this may help reduce bruising. Remove the needle carefully and dispose of it in a sharps bin.
- Stomach (abdomen): Most common choice — inject 5cm away from your belly button and at least 2cm from any existing bruises or marks
- Upper thigh: Pinch the skin and inject at a 90-degree angle
- Upper arm: Another person should pinch the skin and inject for you
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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.
Mounjaro Dose Schedule and Titration
Mounjaro starts at a low dose and increases gradually over weeks. Your prescriber will provide a specific schedule: you begin with 2.5 mg for the first 4 weeks, then move to 5 mg, and continue increasing every 4 weeks up to a maximum of 15 mg. You must stay on each dose for at least 4 weeks before increasing — do not jump doses or increase more frequently. If you experience side effects, your prescriber may keep you on a lower dose for longer or adjust the schedule. Use our GLP-1 weight loss calculator to understand projected weight loss at different doses based on clinical data. Always inject on the same day each week and set a phone reminder to help you remember.
- 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 time of day should I inject Mounjaro?
You can inject Mounjaro at any time of day that suits you — there is no specific requirement to inject at a particular time. Consistency matters more than timing: choose a day and time you can remember easily each week. Many people inject in the morning or evening. Whatever works for your routine is fine.
Can I reuse Mounjaro needles?
No — never reuse needles. Each needle is single-use only. Using a needle more than once risks infection, dulls the needle (making injection painful), and damages the pen mechanism. Always dispose of used needles safely in a sharps bin and use a new needle for each injection.
What if I miss a dose of Mounjaro?
If you remember within 4 days of your missed dose, inject as soon as you remember and continue your normal schedule the following week. If more than 4 days have passed, skip that dose and inject on your normal scheduled day. Never take a double dose. Minimum time between doses is 72 hours.
How do I store my Mounjaro pens?
Unopened pens must be stored in the fridge between 2°C and 8°C — do not freeze. Keep them in the original box away from light. Once you've used a pen for the first time, you can keep it at room temperature (below 30°C) for up to 30 days. After 30 days, dispose of it safely even if there is medicine left.
What should I do if I get side effects like nausea?
Nausea is common, especially when starting or increasing your dose. Eat small, frequent meals and avoid fatty or spicy foods. Stay hydrated and take anti-nausea medication if recommended by your GP. Most people adjust within a few days. If nausea is severe or does not improve, contact your prescriber — they may adjust your dose or timeline.
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.