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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Mounjaro And Shingles — What The Evidence Shows
Shingles is a viral infection caused by reactivation of the chickenpox virus (varicella-zoster). Some people taking weight loss medications like Mounjaro have raised concerns about shingles risk. This guide explains what we know about Mounjaro, tirzepatide, and shingles, how it compares to Wegovy (semaglutide), and what you should discuss with your GP or prescriber before starting any GLP-1 or GIP/GLP-1 medication.
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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, Wegovy, And Shingles Risk — What The Research Shows
Current clinical evidence does not establish a direct causal link between Mounjaro (tirzepatide) or Wegovy (semaglutide) and increased shingles risk. However, both medications have been associated with reports of shingles in real-world use, though causation remains unclear.
Key differences between Mounjaro and Wegovy in this context:
- Mounjaro is a dual GIP and GLP-1 receptor agonist; Wegovy is a GLP-1 agonist only
- Both activate similar appetite and metabolic pathways
- Neither medication directly suppresses immune function in the way immunosuppressive drugs do
- Shingles reports may reflect general population occurrence rather than medication-specific risk
The SURMOUNT clinical trials (Mounjaro) and STEP trials (Wegovy) did not highlight shingles as a primary safety concern. Any shingles cases reported during trials were evaluated within broader safety monitoring. Your prescriber can discuss individual risk factors during your clinical assessment.
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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.
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Your Risk Factors And What To Discuss With Your GP
Shingles risk increases naturally with age (most common in adults over 50), previous chickenpox infection, and certain medical conditions. Weight loss medications do not change these underlying risk factors. Before starting Mounjaro or any GLP-1 medication, discuss with your GP: your age and chickenpox history, any immunocompromise, other medicines you take, and whether shingles vaccination is appropriate for you.
If you develop symptoms like burning pain, tingling, or a rash on one side of your body while taking Mounjaro, contact your GP promptly. This is not necessarily medication-related but requires professional assessment. Use our free GLP-1 weight loss calculator to explore medication options, then discuss all health factors with your prescriber to ensure Mounjaro or Wegovy is right for you.
- 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?
No direct causal link has been established between Mounjaro and shingles in clinical trials. Shingles is caused by reactivation of the chickenpox virus, which is unrelated to how Mounjaro works. Shingles reports in users may reflect natural population occurrence rather than medication effect. Always discuss your individual risk factors with your GP.
Is Wegovy safer than Mounjaro regarding shingles?
No evidence suggests Wegovy carries higher or lower shingles risk than Mounjaro. Both are GLP-1-based medications with similar mechanisms. Clinical trials for both Mounjaro and Wegovy did not identify shingles as a specific safety concern. Your GP can advise based on your personal health history.
Should I get a shingles vaccine before taking Mounjaro?
The NHS offers a shingles vaccine (Shingrix) to adults aged 65 and over, and it's recommended for some younger people with health conditions. Discuss shingles vaccination timing with your GP before starting Mounjaro. Live shingles vaccines (Zostavax) should not be given to people taking certain medications, so professional advice is essential.
What are the real side effects I should watch for with Mounjaro?
Common Mounjaro side effects include nausea, diarrhoea, constipation, and stomach pain—these typically appear in the first few weeks and often improve with time. Serious side effects are rare but include severe stomach pain (pancreatitis), gallbladder issues, and allergic reactions. Report any unusual symptoms to your GP.
How do I know if I have shingles rather than another skin condition?
Shingles typically presents as burning pain followed by a blistering rash on one side of the body. It usually appears on the torso, face, or limbs and is painful before the rash develops. Contact your GP immediately if you suspect shingles—early treatment can reduce severity. Don't wait to see if it's medication-related.
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