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 Injection
If you miss a Mounjaro injection, the action you need to take depends on how long it's been since your scheduled dose. Mounjaro (tirzepatide) is a once-weekly GLP-1 receptor agonist prescription medication, and missing a dose occasionally won't cause serious harm—but understanding the correct steps helps keep your weight management treatment on track. This guide explains NHS and UK prescriber guidance on missed doses, timing, and when to contact your healthcare team for support.
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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 and Guidelines
If you remember within 4 days (96 hours) of your missed dose: Take your Mounjaro injection as soon as you remember, then continue with your regular weekly schedule from that point. For example, if you normally inject on a Monday but remember on Wednesday, inject on Wednesday and then go back to Mondays the following week.
If more than 4 days have passed: Skip the missed dose entirely and take your next injection on your usual scheduled day. Do not take a double dose to make up for the missed one. Your prescriber will have discussed the minimum 72-hour gap between doses—never shorten this interval.
Storage and stability: If your Mounjaro KwikPen has been left unrefrigerated for longer than 30 days, or if you're unsure whether it's still safe, contact your pharmacist or GP before using it. A new pen may be needed.
- Never inject two doses within 72 hours of each other
- Keep a calendar or phone reminder to help avoid missed doses
- Store unopened pens in the fridge (2–8°C); after first use, they can stay at room temperature (below 30°C) for up to 30 days
Clinically BackedWeight Loss
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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 more than one dose in a row, or if you're unsure how to get back on track, contact your GP or the clinic prescribing your Mounjaro. They can confirm the correct next injection date and assess whether your treatment plan needs adjusting. Missing occasional doses is common—healthcare teams are experienced in helping patients restart safely.
If you experience side effects that make you reluctant to continue (such as persistent nausea or stomach pain), discuss alternatives with your prescriber rather than simply stopping. Your GP can explore whether a dose adjustment, timing change, or alternative medication might work better for you. Use our free GLP-1 weight loss calculator to track your progress and discuss results with your healthcare team at your next appointment.
- 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 miss one Mounjaro injection?
If you remember within 4 days, take it as soon as possible and continue your weekly schedule. If more than 4 days have passed, skip that dose and take your next one on your normal day. Missing a single dose won't harm you, but consistency helps with weight management results.
Can I take two Mounjaro doses close together to catch up?
No. The minimum time between Mounjaro doses is 72 hours (3 days). Never inject two doses within this window, even if you've missed a dose. Always contact your prescriber if you're unsure about timing.
Should I tell my GP if I regularly miss doses?
Yes. If you're regularly missing doses, discuss this with your GP or prescriber. They can explore whether timing, side effects, or storage issues are causing the problem and adjust your plan accordingly.
Does missing a Mounjaro dose affect my weight loss progress?
One missed dose is unlikely to significantly impact your results, as Mounjaro acts over a week. However, consistent treatment as prescribed gives the best outcomes. If you've missed multiple doses, discuss this with your healthcare team.
What if my Mounjaro pen was left out of the fridge too long?
If your pen has been at room temperature (above 30°C) or left unrefrigerated for more than 30 days, it may no longer be safe to use. Contact your pharmacist or GP. You may need a replacement pen dispensed under your prescription.
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.