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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How to Take Mounjaro in the UK
Mounjaro (tirzepatide) is a once-weekly prescription injection for weight management available in the UK through NHS specialist services or private prescribers. This guide explains the correct way to take Mounjaro, including dose timing, injection technique, storage requirements, and what to expect during your treatment. Always follow your prescriber's instructions, as dosing is personalised based on your individual health and response. If you're considering Mounjaro, use our free BMI calculator above to check your current status and understand whether you may be eligible under NHS or private criteria.
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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 Injection Technique
Mounjaro is supplied as a pre-filled KwikPen device, with each pen containing 4 weekly doses. Dosing starts at 2.5 mg once weekly, typically increased every 4 weeks to reach an effective maintenance dose (5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg maximum). Your prescriber will determine your personalised schedule based on your response and tolerability.
How to inject Mounjaro:
- Inject once per week on the same day each week (e.g. every Monday)
- Rotate injection sites weekly between stomach, upper thigh, or upper arm
- Clean the injection site with an alcohol wipe; wait for skin to dry
- Pinch skin gently and insert needle at a 90-degree angle
- Press the injection button until you hear a click
- Hold for 6 seconds, then withdraw the needle
- Dispose of used pen in a sharps bin (not household waste)
If you miss a dose within 4 days, take it as soon as remembered. If more than 4 days have passed, skip that dose and take your next injection on the scheduled day.
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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.
Storage and NHS Access in the UK
Storage requirements: Unopened Mounjaro pens must be refrigerated at 2–8°C and kept in their original carton. Once you start using a pen, it can be stored at room temperature (below 30°C) for up to 30 days. Never freeze Mounjaro — if accidentally frozen, do not use it.
NHS access: In the UK, Mounjaro is available through NICE-approved NHS tier 3 specialist weight management services. You'll typically need a GP referral to your local Integrated Care Board service. Access varies significantly by region and waiting lists can be lengthy. Private access is available through UK-licensed online prescribers and GPhC-registered pharmacies without requiring an NHS referral. Our GLP-1 weight loss calculator can help you understand potential outcomes at different doses alongside your individual circumstances.
- 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.
How often do I inject Mounjaro?
Mounjaro is injected once every 7 days (weekly). Choose the same day each week for consistency. If you miss your scheduled injection by up to 4 days, take it as soon as you remember. If more than 4 days have passed, skip that dose and resume your normal weekly schedule. Never inject more frequently than once every 3 days.
What's the starting dose of Mounjaro in the UK?
The starting dose is 2.5 mg once weekly for the first 4 weeks. Your prescriber will then increase your dose every 4 weeks (5 mg, 7.5 mg, 10 mg, 12.5 mg, then 15 mg as maximum) depending on your tolerance and weight loss response. Dose increases are gradual to minimise side effects.
Can I store Mounjaro in my kitchen cupboard?
No. Unopened pens must be refrigerated at 2–8°C in their original carton. Once you start using a pen, it can be kept at room temperature (below 30°C) for up to 30 days. Never freeze Mounjaro, and avoid direct sunlight. Always check the expiry date on your pen before injecting.
How do I get a Mounjaro prescription on the NHS?
You'll need a referral from your GP to your local NHS tier 3 specialist weight management service. Eligibility typically requires BMI ≥30 or BMI 27–29.9 with weight-related health conditions (diabetes, hypertension, or cardiovascular disease). Waiting times vary significantly by region. Private prescription options are also available without NHS referral.
What happens if I inject Mounjaro incorrectly?
If you're unsure you've injected correctly (e.g. needle didn't fully insert), contact your pharmacist or GP immediately. Do not inject again that week — resume your normal weekly schedule the following week. Your prescriber or injection nurse can provide hands-on training to ensure you're injecting properly, and many NHS services offer support calls for confidence.
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.