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 You Need to Know About Mounjaro Extra Doses in the UK
If you're taking Mounjaro (tirzepatide) through the NHS or privately in the UK, you may wonder whether taking an extra dose is ever appropriate. An extra dose should never be taken without explicit guidance from your prescriber. Mounjaro is a prescription-only medicine with a carefully structured dosing schedule designed to help your body adjust safely. This guide explains the NHS approach to dose management, when adjustments happen, and what to do if you've missed or are concerned about your current dose.
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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.
NHS Mounjaro Dosing and When Doses Increase
The NHS prescribes Mounjaro using a standardised dose titration schedule, where you start at 2.5 mg once weekly and gradually increase every 4 weeks if tolerated. The maximum approved dose is 15 mg once weekly.
- Weeks 1–4: 2.5 mg (starting dose)
- Weeks 5–8: 5 mg (first increase)
- Weeks 9–12: 7.5 mg
- Weeks 13–16: 10 mg
- Weeks 17–20: 12.5 mg
- Week 21+: 15 mg (maximum)
Your GP or specialist prescriber will only increase your dose if you've tolerated the previous dose well. Taking an extra dose between scheduled increases is not recommended — it bypasses the safety escalation and increases the risk of side effects like severe nausea or injection site problems. If you feel your current dose isn't working, discuss this with your prescriber rather than taking additional doses.
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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.
What to Do If You've Missed or Taken an Extra Dose
If you've accidentally taken an extra Mounjaro dose, contact your GP or the pharmacy that dispensed it immediately for guidance. In most cases, the next scheduled dose should be taken on your normal day — do not skip it to "catch up." If you've missed a dose within 4 days, take it as soon as you remember and continue your normal weekly schedule. If more than 4 days have passed, skip the missed dose and resume your regular injection day.
Your prescriber may also adjust your dose downward if you're experiencing intolerable side effects — this is a legitimate clinical decision and safer than continuing at a higher dose. Use our free GLP-1 weight loss calculator above to understand how your current dose relates to expected outcomes, and track your progress with our free progress tracker to monitor how well your treatment is working.
- 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.
Can I take an extra Mounjaro dose if I'm not losing weight fast enough?
No. Taking an extra dose is unsafe and not recommended by the NHS or MHRA. Weight loss results vary significantly between individuals. If you're concerned about your progress, discuss this with your prescriber — they may adjust your dose at the scheduled 4-week intervals or explore other options. Sustainable weight loss takes time, typically 3–6 months to see meaningful results.
What happens if I accidentally inject two Mounjaro doses in one week?
Contact your GP or the dispensing pharmacy immediately. In most cases, you'll simply resume your normal weekly schedule the following week. Do not skip your next dose — your prescriber will advise you based on your individual situation. Mounjaro overdose is not an emergency requiring A&E attendance unless you develop severe symptoms like persistent vomiting.
Is the maximum Mounjaro dose of 15 mg higher than Wegovy?
Yes. Mounjaro's maximum approved dose is 15 mg once weekly, while Wegovy (semaglutide) reaches a maximum of 2.4 mg once weekly. This reflects their different mechanisms — Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is GLP-1 only. Both are effective, and your prescriber will choose based on your individual health profile.
How do I know if my Mounjaro dose is right for me?
Your prescriber assesses this based on weight loss progress, side effects, and your overall health. The NHS typically aims to reach an effective dose where you're losing weight steadily (0.5–1 kg per week) with manageable side effects. If side effects are severe, your dose may be kept lower. Calculate your BMI using our free BMI calculator to track your progress against NHS healthy weight targets.
Can I request a higher Mounjaro dose than my prescriber recommends?
Dose decisions are made by your prescriber based on clinical guidelines and your individual safety. If you believe a higher dose might help, discuss your concerns with your GP or specialist — they can explain the reasoning behind your current dose. The NHS follows NICE guidance and MHRA safety protocols, which means prescribers will not exceed recommended escalation unless there's a specific clinical reason.
Ready to take control of your weight loss journey?
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