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 vs Wegovy: How Do the Symptoms Compare?
Both Mounjaro and Wegovy are prescription-only weight management injections available in the UK, but they work slightly differently and may cause different symptoms. Understanding the side effects of each can help you and your GP decide which medication might be more suitable for you. This guide compares the symptoms you might experience with Mounjaro (tirzepatide) versus Wegovy (semaglutide) based on clinical trial data and UK prescribing information. Both medications require a clinical assessment before prescription.
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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.
How Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways in the body. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. This difference in mechanism can influence which side effects are more common with each medication. In the SURMOUNT-1 clinical trial, Mounjaro users reported nausea, diarrhoea, and vomiting as the most frequent symptoms, particularly during dose escalation. Wegovy users in the STEP trials reported similar symptoms but sometimes at slightly different frequencies. Both medications slow gastric emptying (how quickly food leaves your stomach), which contributes to nausea and appetite reduction. The dual mechanism of Mounjaro may explain why some users experience slightly different symptom patterns, though individual experiences vary considerably.
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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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Side-by-Side Symptom Comparison
Very common symptoms (both medications): nausea, diarrhoea, vomiting, constipation, and stomach pain affect more than 1 in 10 users. Common symptoms (both): indigestion, fatigue, dizziness, headache, and injection site reactions occur in up to 1 in 10 users. Hair loss has been reported more frequently with Mounjaro in some studies. Both require clinical assessment to ensure suitability. Use our GLP-1 weight loss calculator to explore potential outcomes, and speak with your GP or prescriber about which medication's symptom profile might work best for your individual circumstances.
- 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.
Which causes more nausea — Mounjaro or Wegovy?
Both cause nausea frequently, particularly during the first 4 weeks and when doses increase. In clinical trials, nausea affected similar proportions of users with both medications. Individual tolerance varies. Most symptoms improve within weeks as your body adjusts. Your prescriber can slow dose escalation if symptoms are bothersome.
Are Mounjaro and Wegovy side effects the same?
Side effects are very similar because both are GLP-1 receptor agonists. Mounjaro's dual mechanism (GIP+GLP-1) may cause slightly different symptom patterns in some users, but clinical data shows substantial overlap. Nausea, diarrhoea, vomiting, and constipation are common to both.
How long do Mounjaro or Wegovy symptoms last?
Most gastrointestinal symptoms improve within 4–8 weeks as your body adapts to the medication. However, some people experience persistent symptoms throughout treatment. Nausea tends to be worst during dose increases. If symptoms remain severe, contact your prescriber — dose adjustments can help.
Can I switch from Mounjaro to Wegovy if I have bad symptoms?
Only a prescriber can recommend switching between medications. Some users switch if they experience persistent side effects, but this requires clinical assessment. Your prescriber may alternatively adjust your dose or suggest strategies to manage symptoms. Always discuss side effects with your GP.
Do Mounjaro or Wegovy cause permanent side effects?
Most side effects are temporary and resolve after stopping the medication or allowing your body to adjust. Serious complications (pancreatitis, gallbladder issues) are rare but require urgent medical attention. Discuss any concerning symptoms with your prescriber immediately. Individual recovery varies.
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.