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
Tips for Taking Mounjaro in the UK
Taking Mounjaro (tirzepatide) successfully means understanding the basics: how to store your KwikPen, when to inject, and what to do if you miss a dose. This guide covers practical tips for using Mounjaro safely under NHS or private prescription in the UK, so you can get the most from your treatment alongside diet and lifestyle changes.
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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.
Storage, Injection Technique, and Dose Timing
Storage is critical for Mounjaro to work properly. Keep unopened KwikPens refrigerated between 2°C and 8°C in their original carton — never freeze them. After your first injection, the pen can stay at room temperature (below 30°C) for up to 30 days, making it convenient to carry. Always check the expiry date before using.
- Rotate injection sites each week to reduce bruising or irritation — use your stomach, upper thigh, or upper arm
- Let the KwikPen sit at room temperature for 15–30 minutes before injecting if it's been refrigerated
- Check the medication is clear and colourless before injecting — if it's cloudy, do not use it
- You must inject once every 7 days — aim for the same day each week to stay on schedule
- If you miss your dose by more than 4 days, skip that week and take your next dose on your regular schedule; never inject if less than 72 hours have passed since your last dose
Take time to familiarise yourself with the KwikPen mechanism before your first injection — your pharmacist can demonstrate the technique.
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.
Managing Side Effects and Staying Safe
Nausea is the most common side effect in the first few weeks, but it usually improves as your body adjusts. Eating smaller, lower-fat meals can help reduce nausea and stomach discomfort. Stay hydrated, avoid high-fat foods, and eat slowly. If side effects persist beyond 4 weeks, speak to your prescriber — they may adjust your dose or offer additional support.
- Report any signs of pancreatitis (severe upper abdominal pain radiating to your back) to your GP immediately
- Monitor your blood sugar if you have diabetes — your other medications may need adjusting
- Use a barrier contraceptive method for 4 weeks after starting and after each dose increase if you take oral contraceptives
- Keep a record of your injections and any side effects — use our free progress tracker to log your experience
- 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.
Can I inject Mounjaro myself at home?
Yes. After initial training from your pharmacist or healthcare provider, you can inject yourself at home weekly. The KwikPen is designed for self-administration. Always follow the instructions provided and ask your pharmacist to demonstrate the technique before your first injection.
What should I do if I forget my weekly Mounjaro injection?
If you remember within 4 days of your missed dose, inject it as soon as you can. Then return to your normal weekly schedule. If more than 4 days have passed, skip that week and take your next dose on your regular day. Never inject twice within 3 days.
Does Mounjaro interact with other medications?
Mounjaro may reduce how quickly your body absorbs oral medications, including oral contraceptives. Inform your prescriber of all medications you take. If you use insulin or diabetes medication, your doses may need adjusting — your GP will monitor this.
How long does it take to see weight loss results with Mounjaro?
Clinical trials showed gradual weight loss over 16 weeks and beyond. Most people see noticeable changes by week 8–12, though individual results vary significantly. Use our free weight loss calculator to estimate potential outcomes based on your dose.
Can I stop taking Mounjaro whenever I want?
You can stop at any time, but discuss this with your prescriber first. Some people experience weight regain after stopping. Your GP can advise you on the best approach based on your individual health goals and circumstances.
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.