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 to Use Mounjaro: UK Instructions and Comparison
Mounjaro (tirzepatide) is a once-weekly injection used for weight management in the UK. This guide explains the practical steps to using your Mounjaro KwikPen, the dosing schedule, storage requirements, and how the injection method compares to Wegovy. Both are prescription-only medicines that require a clinical assessment before being prescribed. Individual suitability depends on your health profile, which your prescriber will assess during your consultation.
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.
How to Use Mounjaro: Injection Technique and Dosing
Mounjaro comes as a pre-filled KwikPen device containing four weeks' worth of doses. Each pen delivers a single once-weekly injection. You inject the same dose every seven days, ideally on the same day each week.
Injection sites: Mounjaro can be injected into your stomach (abdomen), upper thigh, or upper arm. Rotate your injection site each week to reduce irritation. You can inject into the same general area but use a different spot within that area each time.
- Gently pinch the skin at your chosen site
- Insert the needle at a 90-degree angle
- Press and hold the button until you hear two clicks (takes about 6 seconds)
- Wait 10 seconds after the second click before removing the pen
- Release the pinched skin and dispose of the pen safely in a sharps bin
Storage: Unopened pens must be refrigerated at 2–8°C. Once you start using a pen, you can keep it at room temperature (below 30°C) for up to 30 days. Never freeze Mounjaro. Keep pens in their original carton away from direct sunlight.
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.
Mounjaro vs Wegovy: How They Compare in Practice
Both Mounjaro and Wegovy are once-weekly injections for weight management, but they work differently. Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways. Wegovy is a GLP-1 receptor agonist only, activating one pathway. In clinical trials, Mounjaro showed an average weight loss of 15–21% of body weight, while Wegovy showed approximately 15% — though individual results vary significantly.
The practical use is identical: both are once-weekly KwikPen injections. Mounjaro's dose range starts at 2.5 mg and goes up to 15 mg. Wegovy starts at 0.25 mg and reaches 2.4 mg. Your prescriber will decide which is more suitable based on your health profile and medical history. Neither is superior — suitability is individual.
Both medications require a prescription and clinical assessment before use. UK access is through NHS specialist weight management services or private online prescribing services following clinical review. If you miss a dose, take it within four days and continue your normal schedule. Both cause similar side effects initially (nausea, diarrhoea, constipation) which typically ease as your body adjusts. Track your progress using our free progress tracker to monitor weight changes alongside your other health markers.
- 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 do I inject Mounjaro correctly?
Pinch the skin at your chosen injection site (stomach, thigh, or upper arm), insert the needle at 90 degrees, press the button until you hear two clicks (about 6 seconds), wait 10 seconds, then remove. Rotate injection sites each week. Always dispose of pens in a sharps bin.
What's the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP+GLP-1 agonist; Wegovy is GLP-1 only. Mounjaro doses go up to 15 mg weekly; Wegovy up to 2.4 mg weekly. Clinical trial weight loss averages are similar (15–21% for Mounjaro, ~15% for Wegovy). Your prescriber will recommend the most suitable option for you.
How should I store my Mounjaro KwikPen?
Unopened pens must be refrigerated at 2–8°C in their original carton. Once you start using a pen, it can stay at room temperature (below 30°C) for 30 days. Never freeze Mounjaro. Discard the pen after 30 days of use, even if it contains remaining doses.
What do I do if I miss a Mounjaro dose?
If you remember within four days of your missed dose, take it as soon as you can and continue your normal weekly schedule. If more than four days have passed, skip that dose and take your next dose on your usual day. Never take a double dose.
Which is easier to use, Mounjaro or Wegovy?
Both use identical KwikPen injection devices and are injected once weekly. The injection technique is the same. The difference is in dosing schedules and mechanism of action, not ease of use. Your GP or prescriber will determine which is clinically appropriate for you based on your health profile.
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.