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've Missed a Week of Mounjaro
If you've missed a week of your Mounjaro injection, don't panic — there are clear steps to follow to get back on track. Mounjaro (tirzepatide) is a once-weekly GLP-1 receptor agonist prescribed for weight management, and missing a single dose won't cause serious harm. However, knowing the right action to take will help you maintain the effectiveness of your treatment and stay aligned with your dose titration schedule. This guide covers what you should do, when to contact your prescriber, and how to prevent missed doses in future.
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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.
When to Take Your Missed Mounjaro Dose
The timing of your missed dose matters. If you're within 4 days of your scheduled injection date, take the missed dose as soon as you remember. After taking it, continue with your normal weekly schedule the following week — don't adjust your next dose or try to "catch up" by doubling up.
If more than 4 days have passed since your scheduled injection, skip the missed dose entirely and resume your normal schedule with your next weekly injection on your usual day.
- Within 4 days: inject as soon as remembered, continue normal schedule
- After 4 days: skip, resume next week as normal
- Never double-dose or inject within 72 hours of your last injection
- A KwikPen contains 4 weeks of doses — one missed injection doesn't waste the pen
If you're unsure about timing, contact your prescriber or pharmacist for personalized guidance. Consistency is important for dose titration, but one missed week won't derail your progress.
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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.
Avoiding Future Missed Doses — Practical Tips
Setting reminders is one of the easiest ways to avoid missing your weekly injection. Use your phone calendar with a notification a day before your scheduled date, or set a repeating alarm on the day itself.
Store your Mounjaro KwikPen in a visible location — the fridge door or a designated shelf in your bathroom — so it's top of mind when it's time to inject. Some people find it helpful to link their injection to an existing weekly routine, such as a Sunday evening or Wednesday morning.
- Phone reminders (calendar or app) set for your injection day
- Keep your KwikPen visible in the fridge, not hidden at the back
- Link injection to a weekly habit (e.g., after Sunday dinner)
- Tell a family member or friend your injection day so they can remind you
If you travel, plan ahead: check storage requirements for your destination and carry your prescription details in case you need replacement pens.
- 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.
Will missing one Mounjaro injection affect my weight loss?
Missing a single weekly dose is unlikely to cause significant weight loss setback. However, consistency helps maintain the medication's effectiveness over time. If you miss occasional doses, resume your normal schedule and don't compensate by taking extra doses. One missed injection won't restart your progress — just get back on track the following week.
What if I've missed more than one week of Mounjaro?
If you've missed multiple weeks, contact your prescriber or the pharmacy where you obtained your prescription before restarting. They may advise resuming your current dose or stepping back to a lower dose depending on how long you've been off treatment. Never restart at your highest dose after a prolonged break without guidance.
Can I get a replacement KwikPen if I wasted a dose?
This depends on your prescriber and whether you have a valid prescription. Contact the pharmacy or prescriber who dispensed your Mounjaro — they can advise whether a replacement is available and any associated costs. NHS patients should contact their specialist weight management service; private patients should contact the online pharmacy or clinic that issued their prescription.
Does missing Mounjaro mean I need to restart my dose titration?
No. If you've missed one week, you don't restart titration — simply resume your current dose the following week. Dose titration (the schedule of gradually increasing your dose every 4 weeks) is designed with the assumption that most people will maintain weekly injections. One missed dose doesn't disrupt this schedule.
How do I know if I need to contact my GP or prescriber about a missed dose?
Contact your prescriber if: you've missed more than one week, you're unsure about timing, you've had severe side effects before missing a dose, or you're considering stopping treatment. For a single missed dose within 4 days, you can usually resume independently. For prescription or access issues, contact the pharmacy or clinic that supplies your Mounjaro.
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.