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 Mounjaro Cause Thrush?
Thrush (a yeast infection caused by Candida) is not commonly reported as a direct side effect of Mounjaro in clinical trials. However, some GLP-1 and dual GIP/GLP-1 medications like tirzepatide (Mounjaro's active ingredient) may indirectly increase thrush risk by slowing digestion or affecting gut bacteria. This page compares Mounjaro and Wegovy to help you understand the side effect profile of each, so you can make an informed decision with your prescriber.
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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 Yeast Infection Risk
Thrush is not listed as a common or very common side effect of either Mounjaro or Wegovy in their official UK prescribing information. However, both medications work on the GLP-1 pathway (Mounjaro also activates GIP), which can affect digestive speed and potentially alter the balance of bacteria and fungi in the gut. This indirect mechanism might increase susceptibility to thrush in some individuals, though this is not formally documented in clinical trials.
Neither the SURMOUNT trials (Mounjaro) nor the STEP trials (Wegovy) reported thrush as a significant adverse event. Side effects most commonly reported include nausea, diarrhoea, constipation, and stomach pain. If you develop symptoms of thrush—such as vaginal itching or discharge (women), penile irritation (men), or oral white patches—contact your GP promptly for assessment and treatment.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Comparing Mounjaro and Wegovy Side Effect Profiles
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only GLP-1 receptor agonists approved in the UK for weight management. The key difference is that Mounjaro uses a dual GIP and GLP-1 mechanism, whilst Wegovy is GLP-1 only. In clinical practice, both have similar side effect profiles—gastrointestinal symptoms dominate, with nausea and diarrhoea most frequent.
Individual side effect experiences vary significantly. Some people experience very few symptoms, whilst others find gastrointestinal effects challenging. Your prescriber will monitor you during dose titration and can adjust your Mounjaro KwikPen dose or switch medications if needed. Use our free GLP-1 weight loss calculator to explore potential outcomes, and discuss any specific health concerns with your GP or prescriber before starting treatment.
- 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.
Is thrush a known side effect of Mounjaro?
Thrush is not listed as a common side effect of Mounjaro in clinical trials or UK prescribing information. However, any medication that affects digestion could theoretically increase yeast infection risk. If you develop thrush symptoms whilst taking Mounjaro, contact your GP—this may be coincidental, not caused by the medication itself.
Does Wegovy cause thrush?
Like Mounjaro, thrush is not a documented side effect of Wegovy. Both medications' most common side effects are gastrointestinal (nausea, diarrhoea, constipation). If you develop thrush whilst taking Wegovy, discuss this with your GP to explore potential causes and treatment options.
What are the most common side effects of Mounjaro?
The most common Mounjaro side effects reported in SURMOUNT trials are nausea, diarrhoea, vomiting, constipation, and stomach pain. These typically improve as your body adjusts to the medication. Dose titration—starting at 2.5 mg and increasing gradually—helps reduce symptom severity. Discuss any persistent side effects with your prescriber.
Can GLP-1 medications affect gut health?
GLP-1 medications like Wegovy and Mounjaro slow gastric emptying (how quickly food leaves the stomach), which can affect digestive comfort and potentially alter gut bacteria balance. This may theoretically increase infection risk in some people, though clinical evidence for thrush specifically is lacking. Maintaining good hygiene and a balanced diet may help support gut health whilst taking these medications.
Should I stop Mounjaro if I develop thrush?
Do not stop Mounjaro without speaking to your prescriber. If you develop thrush symptoms, contact your GP immediately. Thrush is treatable with antifungal medication (typically fluconazole or topical creams in the UK). Your GP can assess whether the thrush is related to Mounjaro or another cause, and recommend appropriate treatment without stopping your weight management medication.
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