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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Can I Skip A Week Of Mounjaro?
If you're taking Mounjaro (tirzepatide) as a prescription weight management injection in the UK, you may wonder what to do if you need to miss a dose. The answer depends on how long it's been since your last injection. Generally, you can take a missed dose within 4 days of the scheduled date, but if it's been longer, you should skip that dose and continue on your normal schedule. Always speak to your GP or prescriber if you're unsure about timing, as consistency matters for the medication to work effectively alongside your diet and lifestyle changes.
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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 Dosing Schedule And Missed Doses
Mounjaro is a prescription-only, once-weekly injection — consistency is important for the medication to work as intended. Each KwikPen dose is given exactly 7 days apart. Here's the NHS and MHRA guidance on missing a dose:
- Within 4 days of your scheduled dose: Take the injection as soon as you remember, then continue your normal weekly schedule from that date.
- More than 4 days since your scheduled dose: Skip the missed dose completely. Take your next dose on your normal scheduled day (7 days after the missed dose would have been).
- Never take a double dose to make up for a missed one — this increases the risk of side effects.
- Minimum spacing: Never give yourself two doses within 72 hours (3 days) of each other.
If you're uncertain about the timing, contact your prescriber or pharmacist immediately — they can advise based on your specific dosing history. UK prescribers and pharmacists have access to your injection dates in your medical records.
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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
You should contact your GP or prescriber if you've missed more than one dose, if you're unclear about your dosing schedule, or if you're having difficulty taking your Mounjaro injections regularly. They may discuss whether the medication is still suitable for you, or whether additional support (such as a sharps bin reminder system or pharmacy support) would help.
Do not stop taking Mounjaro without speaking to your prescriber first. Stopping suddenly may mean you lose the weight loss progress you've made, and your prescriber needs to monitor this. Whether you access Mounjaro through NHS tier 3 services or privately, your prescriber has a duty of care to support consistent, safe use of the medication alongside your reduced-calorie diet and physical activity plan.
- 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 a Mounjaro injection by a few days?
If you remember within 4 days of your scheduled date, take the dose immediately and resume your normal weekly schedule. For example, if you were due on Monday but inject on Wednesday, your next dose would be due the following Wednesday. Always contact your prescriber if you're unsure.
Can I take two Mounjaro doses close together to make up for a missed week?
No. Never take two doses within 72 hours of each other — this increases side effect risk. If you've missed more than 4 days, skip that dose and continue your normal schedule. Your prescriber or pharmacist can confirm the safest timing.
What if I've skipped multiple weeks of Mounjaro — is it still effective?
Consistency is important for Mounjaro to work effectively. Missing doses means you may not see the expected weight loss results. Speak to your prescriber about restarting or continuing. They can reassess whether the medication is still right for you based on your situation.
Does missing a dose of Mounjaro affect my BMI or weight loss progress?
Missing a single dose is unlikely to cause significant weight regain, but missing multiple doses may slow your progress. Weight loss with Mounjaro is achieved alongside reduced-calorie diet and physical activity — consistency with injections helps maintain the medication's effect.
Is there a grace period for Mounjaro doses on the NHS vs private prescription?
The 4-day window applies to both NHS and private Mounjaro prescriptions — this is MHRA guidance that all UK prescribers follow. Whether you access Mounjaro through NHS tier 3 services or a private prescriber, the dosing rules are the same. Your pharmacist or prescriber can clarify your specific 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.