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
Mounjaro And Shingles — What The Evidence Shows
There is currently no established direct link between Mounjaro (tirzepatide) and shingles in clinical trial data or approved prescribing information. However, because Mounjaro may affect how your immune system functions and because shingles is caused by reactivation of the varicella-zoster virus (the virus that causes chickenpox), it is reasonable to discuss any concerns about shingles risk with your GP. This guide explains what we know about Mounjaro's immune effects and when to seek medical advice.
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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.
How Mounjaro Affects Your Immune System
Mounjaro is a dual GIP and GLP-1 receptor agonist — it works by mimicking two natural hormones that regulate appetite and blood sugar. Unlike some medications, Mounjaro is not an immunosuppressant and is not designed to suppress your immune function.
However, gradual weight management itself can temporarily affect immune function, as your body adjusts to significant changes. Additionally, GLP-1 agonists may have mild effects on inflammation and immune markers in some people. The relationship between these changes and shingles risk is not well-established in current evidence.
If you have a personal or family history of shingles, or if you are concerned about your individual risk, discuss this with your GP before starting Mounjaro. Your prescriber can review your medical history and help determine whether this medication is appropriate for you.
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.
Shingles Risk And When To Seek Advice
Shingles (herpes zoster) becomes more common with age and is most prevalent in adults over 50. Your risk is higher if you have had chickenpox before, a weakened immune system, or significant stress. You cannot catch shingles from Mounjaro itself.
If you develop a painful rash, blistering, or burning sensation on one side of your body whilst taking Mounjaro, contact your GP immediately. Early treatment of shingles can reduce severity and complications. Keep your GP informed of any new symptoms, especially if they appear unusual or persistent, as they can assess whether they are related to Mounjaro or to another cause.
For questions about your individual risk or to discuss whether Mounjaro is suitable for you, arrange a consultation with a prescriber or your GP.
- 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 Mounjaro cause shingles?
There is no evidence that Mounjaro directly causes shingles. Shingles is caused by reactivation of the varicella-zoster virus from chickenpox. Mounjaro is not an immunosuppressant, though weight loss itself may temporarily affect immune markers. If you are concerned, discuss your individual risk with your GP.
Should I avoid Mounjaro if I am at high risk of shingles?
Not necessarily. Current evidence does not contraindicate Mounjaro for shingles risk. However, if you have significant immune concerns or previous shingles episodes, discuss this with your prescriber during your clinical assessment. They can evaluate your full medical history and advise whether Mounjaro is right for you.
What should I do if I develop a rash while taking Mounjaro?
Contact your GP promptly. Describe the rash's location, pattern, and any associated pain or blistering. Your GP can examine you and determine whether it is shingles or another condition. Early shingles treatment is most effective, so seek advice quickly rather than waiting to see if it resolves.
Does Mounjaro affect my varicella or shingles vaccine?
There is limited specific guidance on this. If you are due for a shingles vaccine (such as Shingrix), discuss timing with your GP or prescriber. Some vaccines are better given before starting certain medications, so a personalised discussion with your healthcare team is important.
How do I know if I am eligible for Mounjaro?
Mounjaro may be prescribed to adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions. Eligibility depends on your full health picture, which your prescriber will assess during your clinical consultation. Use our free BMI calculator above to check your starting point.
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.