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
What To Do If You Forgot Your Mounjaro Injection
If you've missed your weekly Mounjaro injection, the most important thing is knowing the right steps to take next. The guidance depends on how long it's been since your scheduled dose. This NHS-aligned information explains what to do, when to contact your prescriber, and how to get back on track with your tirzepatide treatment.
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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.
Mounjaro Missed Dose Guidance — Key Rules
If you remember within 4 days of your missed dose: Take your injection as soon as you remember, then continue with your normal weekly schedule from that point. Do not take a double dose to make up for the missed one.
If more than 4 days have passed: Skip the missed dose entirely and take your next injection on your normal scheduled day. This keeps you aligned with your weekly routine.
Minimum spacing between doses: Always leave at least 72 hours (3 days) between Mounjaro injections. Never inject sooner than this, even if you've missed a dose.
Storage and your KwikPen: Check that your Mounjaro KwikPen hasn't been kept outside the correct temperature range. Unopened pens should be refrigerated at 2–8°C. Once you've started using a pen, it can be stored at room temperature below 30°C for up to 30 days, then must be discarded.
Your prescriber or pharmacy can advise on your specific circumstances, especially if you're unsure how much time has passed or if you're taking other medications that might interact.
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.
When To Contact Your GP or Prescriber
If you've missed more than one dose in a row, or if you're uncertain about the timing, contact your GP or the prescriber who issued your Mounjaro prescription. They can confirm the correct next steps and may need to adjust your injection schedule if several doses have been missed.
If you're experiencing side effects that made you skip the injection — such as severe nausea or stomach pain — tell your prescriber. They may suggest a dose adjustment or additional support. Never stop taking Mounjaro suddenly without medical guidance, as this can affect blood sugar control if you have type 2 diabetes.
For NHS patients receiving Mounjaro through a tier 3 specialist weight management service, contact the service directly with any concerns. Your prescriber's contact details will be on your prescription paperwork.
- 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 normal schedule. If more than 4 days have passed, skip it and take your next dose on your regular day. Always maintain at least 72 hours between injections. The most important thing is getting back on your weekly routine without doubling up on doses.
Can I take two Mounjaro injections close together to catch up?
No, never take two doses close together. The minimum spacing between Mounjaro injections is 72 hours (3 days). Taking a double dose or injecting too soon risks increasing side effects and is not medically safe. Follow the 4-day rule: within 4 days, take it; after 4 days, skip it.
How does a missed dose affect my weight loss with Mounjaro?
One missed dose is unlikely to significantly impact your overall weight loss progress, especially if you catch it within 4 days. However, missing multiple doses in a row may affect appetite regulation and consistency. Staying on your weekly schedule is important for steady results. Your GP or prescriber can advise if you're concerned about progress.
Should I tell my GP if I regularly forget my Mounjaro injection?
Yes. If you're having difficulty remembering your weekly injection, tell your prescriber or GP. They may suggest strategies like setting phone reminders, marking your calendar, or choosing a specific day each week (e.g., every Sunday). Some people find keeping their Mounjaro KwikPen visible as a visual reminder helpful too.
What if I accidentally took my Mounjaro injection twice in one week?
Contact your prescriber or GP immediately. They may advise monitoring for increased side effects like nausea, vomiting, or stomach pain. In future, mark off each injection on a calendar or use a reminder app to avoid accidental double-dosing. Your prescriber will confirm whether your next dose timing needs adjustment.
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.