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
Can I Take 2 Mounjaro 2.5mg Shots in One Week?
No — you should never take 2 Mounjaro 2.5mg shots in one week. Mounjaro is a once-weekly injection, and taking double doses or injecting more frequently is unsafe and not approved by the MHRA. The standard Mounjaro KwikPen delivers one dose per week, and your prescriber will guide your dose titration schedule. If you're unsure about your dosing or have concerns about your current dose, always speak to your GP or the healthcare professional who prescribed your Mounjaro.
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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.
How Mounjaro Dosing Works in the UK
Mounjaro (tirzepatide) is a once-weekly injection only. The UK dosing schedule follows strict guidelines to ensure safety and effectiveness. You start at 2.5mg weekly for the first 4 weeks, then your prescriber may increase your dose by 2.5mg increments every 4 weeks, up to a maximum of 15mg per week. Each KwikPen contains 4 weeks of doses — one pen = one injection per week for 4 weeks.
- Week 1–4: 2.5mg once weekly
- Week 5–8: 5mg once weekly (if dose escalated)
- Week 9–12: 7.5mg once weekly (if escalated)
- Week 13+: Continue escalating by 2.5mg increments every 4 weeks, up to 15mg maximum
Taking 2 doses in one week would mean you receive 2–5mg more tirzepatide than is safe for your body at that stage. This increases risk of serious side effects including severe nausea, vomiting, and gastrointestinal problems. Never skip a dose, double dose, or inject more than once per week.
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.
What to Do If You've Missed a Dose or Miscalculated
If you've accidentally taken 2 Mounjaro injections within a short timeframe, contact your GP or NHS 111 immediately for guidance. If you've simply missed your regular weekly injection, follow MHRA guidance: inject within 4 days of your scheduled date and continue your normal weekly schedule afterward. Do not inject twice to "catch up." If more than 4 days have passed since your missed dose, simply skip it and resume your normal weekly injection schedule. Using our free GLP-1 weight loss calculator can help you track when your injections are due, and maintaining consistent once-weekly timing helps your body adjust safely to the tirzepatide.
- 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 happens if I take 2 Mounjaro shots in one week?
Taking 2 Mounjaro injections in one week is unsafe and not approved. Mounjaro is strictly a once-weekly injection. Double dosing increases risk of severe nausea, vomiting, diarrhoea, and other serious gastrointestinal side effects. Your body needs 7 days between injections to process the medication safely. Always stick to your prescribed once-weekly schedule.
Can I increase my Mounjaro dose faster than every 4 weeks?
No. NHS guidance and MHRA approval require a minimum of 4 weeks between dose increases. This allows your body to adjust to each dose level and helps your prescriber assess how well you're tolerating the medication. Faster escalation is not safe and is not recommended by any licensed UK prescriber.
I missed my Mounjaro injection — should I take 2 next week?
No. If you miss your dose, inject within 4 days of your scheduled date and resume your normal weekly schedule. If more than 4 days have passed, skip that dose entirely and inject on your next regular weekly day. Never take 2 injections in one week to compensate for a missed dose.
What's the difference between Mounjaro vs Wegovy dosing schedules?
Both are once-weekly injections, but doses differ. Mounjaro (tirzepatide) starts at 2.5mg weekly, escalating to a maximum of 15mg. Wegovy (semaglutide) starts at 0.25mg weekly, escalating to 2.4mg maximum. Both follow strict 4-week escalation intervals. Your prescriber will advise on which is appropriate for you based on your health needs and UK eligibility criteria.
Where can I find my injection schedule and avoid dosing errors?
Your prescriber will provide detailed written dosing instructions with your Mounjaro KwikPen. Mark your calendar with your weekly injection day. If you want extra support tracking your doses, our free progress tracker helps you log your weekly injections and monitor your weight loss journey safely alongside your prescribed medication schedule.
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.