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 Mouth Ulcers vs Wegovy โ What You Need to Know
Mouth ulcers are not listed as a common or very common side effect of either Mounjaro (tirzepatide) or Wegovy (semaglutide) in UK clinical trials, though oral discomfort and changes to eating patterns may occur with both medications. Both are prescription-only weight management injections available in the UK following clinical assessment. Understanding how they differ โ and which may suit you โ requires looking at their mechanisms, trial data, and individual suitability. This guide compares the two fairly so you can discuss options with your GP or prescriber.
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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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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 and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist โ it activates two natural hormone pathways simultaneously. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) work together to regulate appetite, reduce food cravings, and slow gastric emptying. In the SURMOUNT-1 clinical trial, participants on Mounjaro lost an average of 20.9% of their body weight at the maximum dose (15 mg) over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1-only receptor agonist โ it activates just the GLP-1 pathway. In the STEP-1 clinical trial, participants on Wegovy 2.4 mg lost an average of 14.9% of their body weight over 68 weeks under the same lifestyle conditions. Both medications slow how quickly food leaves the stomach, which reduces gradually over time. The key difference is mechanism: Mounjaro's dual action may provide additional appetite control through the GIP pathway.
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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 โ all stored privately in your browser.
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Mouth Ulcers and Other Oral Side Effects โ What the Trials Show
Neither SURMOUNT (Mounjaro) nor STEP (Wegovy) trials listed mouth ulcers as a reported adverse event. However, both medications can affect eating and swallowing โ nausea and reduced appetite are very common side effects โ which may indirectly affect oral health if nutrition or oral hygiene changes. Some users report dry mouth or altered taste sensation, which may increase ulcer risk if combined with reduced saliva. If you develop mouth ulcers whilst on either medication, inform your prescriber immediately โ mouth ulcers can occasionally signal other underlying issues. Your GP can assess whether the medication should continue or if additional oral care is needed. Use our free GLP-1 weight loss calculator to explore potential outcomes, and discuss specific side effect concerns during your clinical assessment.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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.
Are mouth ulcers a known side effect of Mounjaro?
Mouth ulcers are not listed as a common side effect in UK clinical trials of Mounjaro. Very common side effects include nausea, diarrhoea, vomiting, and constipation. If you develop mouth ulcers whilst taking Mounjaro, inform your prescriber or GP โ they can assess whether it's related to the medication or another cause.
What about Wegovy โ does it cause mouth ulcers?
Mouth ulcers are not reported as a common side effect of Wegovy in STEP trials either. Very common side effects are nausea, diarrhoea, vomiting, and constipation. Changes to eating patterns and reduced appetite may indirectly affect oral health, but direct ulceration is not a typical reported adverse event.
Which medication has fewer side effects โ Mounjaro or Wegovy?
Both medications have similar very common side effects (nausea, diarrhoea, vomiting, constipation). Clinical trial data shows Mounjaro may produce greater average weight loss, but this doesn't mean fewer side effects. Individual tolerability varies significantly. Your prescriber will assess which suits your health profile during clinical assessment.
Can dry mouth from Mounjaro or Wegovy cause mouth ulcers?
Dry mouth can increase ulcer risk by reducing protective saliva, though it's not a commonly reported side effect of either medication. If you experience dry mouth, stay well-hydrated and maintain good oral hygiene. Discuss persistent oral symptoms with your GP or dentist to rule out other causes.
How do I access Mounjaro or Wegovy in the UK?
Both are prescription-only medications available through NHS specialist weight management services (tier 3) or private online prescribing following clinical assessment. You'll need a consultation with a UK-licensed prescriber who will review your eligibility, medical history, and suitability. The KwikPen (Mounjaro) and auto-injection pen (Wegovy) require weekly injections. Your prescriber will discuss all side effects, including oral concerns.
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