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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What to Do If You Miss a Mounjaro Dose
Missing a Mounjaro injection can feel worrying, but there's a clear guidance protocol you should follow. Mounjaro is a once-weekly GLP-1 and GIP receptor agonist prescribed for weight management in the UK, and maintaining consistent dosing is important for effectiveness. This guide explains what to do if you've missed your scheduled dose, based on NHS and MHRA prescribing guidance. The key rule is simple: if you remember within four days, take your dose as soon as possible and continue your normal weekly schedule from there.
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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 Missed Dose Timing Rules
The timing of your missed dose matters significantly. If you remember within four days (96 hours) of your scheduled injection day, take your dose immediately and then resume your normal weekly schedule. For example, if you normally inject on Mondays and remember on Thursday, inject Thursday and continue injecting on your next scheduled Monday.
If more than four days have passed since your scheduled dose, skip that dose entirely and take your next injection on your normally scheduled day. Never take a double dose or two doses within three days of each other. The minimum time between tirzepatide injections must be at least 72 hours (three days). This applies whether you're using a Mounjaro KwikPen at doses ranging from 2.5 mg through to the maximum 15 mg dose.
- Within 4 days: inject immediately, continue normal schedule
- More than 4 days: skip, resume normal schedule next week
- Never double-dose or inject within 72 hours
- If unsure, contact your prescriber or pharmacist
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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.
When to Contact Your GP or Prescriber
If you've missed a dose and feel uncertain about the timing, don't guess—contact your prescriber, GP, or the pharmacy that supplied your medication. This is especially important if you've missed multiple doses, if you're in the dose titration phase (where you increase by 2.5 mg every four weeks), or if you've experienced storage issues with your KwikPen.
Your prescriber may also want to know if missed doses are becoming a pattern, as they can review your administration technique or storage practices. Keep your Mounjaro in the fridge at 2–8°C before use and at room temperature (below 30°C) for up to 30 days after first use. Protect it from light and never freeze it.
If you've missed a dose and feel uncertain about the timing, don't guess—contact your prescriber, GP, or the pharmacy that supplied your medication. This is especially important if you've missed multiple doses, if you're in the dose titration phase (where you increase by 2.5 mg every four weeks), or if you've experienced storage issues with your KwikPen. Your prescriber may also want to know if missed doses are becoming a pattern, as they can review your administration technique or storage practices. Keep your Mounjaro in the fridge at 2–8°C before use and at room temperature (below 30°C) for up to 30 days after first use. Protect it from light and never freeze it.
- 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 if I'm more than four days late with my Mounjaro injection?
Skip that dose and inject on your normally scheduled day the following week. Taking it late defeats the dose timing cycle. Never take two doses within 72 hours. Contact your prescriber if you're unsure about your schedule or if this becomes a regular issue.
Can I take Mounjaro two days in a row if I've missed a dose?
No. Mounjaro must be injected at least 72 hours (three days) apart. Never take two doses within this timeframe, even if you've missed a previous dose. Maintain at least three days between injections to avoid safety concerns and maintain the intended therapeutic effect.
Does missing one Mounjaro dose affect my weight loss progress?
One missed dose is unlikely to significantly impact your overall progress, especially if you're maintaining healthy eating habits and activity levels. However, consistency with GLP-1 and GIP receptor agonists like tirzepatide does support steady results. If you're frequently missing doses, discuss strategies with your GP or prescriber.
How should I store my Mounjaro KwikPen to prevent the need to discard it?
Before first use, store unopened pens in the fridge at 2–8°C in the original carton. After first use, you can store at room temperature (below 30°C) for up to 30 days. Never freeze. Mark the date you opened the pen and discard it after 30 days. Proper storage prevents spoilage and wasted doses.
What if I'm on dose titration—does missing a dose delay my increase schedule?
This depends on your prescriber's guidance. If you're in the titration phase (increasing from 2.5 mg to 5 mg to 7.5 mg, etc.) and miss a dose, you may need to delay your next scheduled increase. Contact your prescriber before increasing your dose if you've missed a previous injection.
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.