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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10mg Mounjaro Side Effects vs Wegovy
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work differently and have distinct side effect profiles. At the 10mg dose, Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 agonist only. Understanding how these medications differ—and what side effects clinical trials actually showed—helps you and your GP or prescriber make an informed decision about which option might suit you best. Both require clinical assessment before prescription.
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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.
Clinical Trial Data and Mechanism Differences
Mounjaro (tirzepatide) at 10mg activates two hormone pathways: GIP and GLP-1. In the SURMOUNT-1 trial, participants on 10mg lost an average of 19.5% body weight over 72 weeks, alongside reduced-calorie diet and physical activity. The most common side effects were nausea (29%), diarrhoea (23%), and vomiting (9%). Gastrointestinal effects were most pronounced during dose escalation and often lessened over time.
Wegovy (semaglutide) at maximum dose 2.4mg activates GLP-1 only. In the STEP-1 trial, average weight loss was approximately 14.9% body weight at 68 weeks. Nausea occurred in 25% of participants, diarrhoea in 20%, and vomiting in 7%. Because semaglutide has a single mechanism compared to tirzepatide's dual action, the side effect intensity patterns differ slightly, though nausea and gastrointestinal effects remain most common.
The mechanism difference means Mounjaro's additional GIP pathway may contribute to greater average weight loss but also potentially greater appetite suppression—which some experience as more pronounced nausea initially.
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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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Which Is More Suitable for You?
Choosing between 10mg Mounjaro and Wegovy is a decision between you and your prescriber, not a straightforward "better" option. Some people tolerate one better than the other. Factors your GP or prescriber will consider include: your individual health history, any previous medication tolerance, whether you need the dual GIP+GLP-1 mechanism (Mounjaro), or prefer a single GLP-1 approach (Wegovy), and UK prescription availability in your region.
Both medications require a prescription and clinical assessment. NHS access is through specialist tier 3 weight management services; private access is via online prescribers. Use our free GLP-1 weight loss calculator to explore projected outcomes at different doses, and discuss individual suitability with your healthcare provider. Your BMI, weight-related health conditions, and personal tolerance are what matter most.
- 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.
Does 10mg Mounjaro cause worse side effects than Wegovy?
Not necessarily worse—different. Clinical trials show both cause similar side effects (nausea, diarrhoea), but at different rates. Mounjaro's dual mechanism may cause slightly more pronounced appetite suppression; Wegovy's single GLP-1 pathway is gentler for some people. Individual tolerance varies significantly. Side effects also depend on dose escalation speed and whether you've taken GLP-1 medications before.
How long do side effects last on 10mg Mounjaro?
Most side effects peak during dose escalation and typically improve within 2–4 weeks once you stabilise at your target dose. Nausea and gastrointestinal effects often become much milder by week 8–12. Some people experience persistent mild nausea, whilst others report complete resolution. Your prescriber monitors your tolerance throughout.
Can I switch from Mounjaro to Wegovy if I get side effects?
Yes, switching is possible and should be managed by your prescriber. There is no official conversion between the two, but approximate clinical equivalence exists (10mg Mounjaro ≈ 1.7mg Wegovy). Any switch requires a new prescription and assessment. Some people tolerate one significantly better than the other.
Which has fewer gastrointestinal side effects—Mounjaro or Wegovy?
Wegovy may cause slightly fewer GI effects for some people because it uses a single GLP-1 mechanism rather than dual GIP+GLP-1. However, clinical trial data shows both have similar rates of nausea and diarrhoea overall. Individual experience varies—some people on Mounjaro have minimal GI effects; others on Wegovy experience significant nausea.
Do I need NHS approval or private prescription for 10mg Mounjaro vs Wegovy?
Both require a prescription from a UK-licensed prescriber following clinical assessment. NHS access is through specialist weight management services (tier 3); availability varies by region and involves waiting lists. Private prescribing is available online without NHS referral. Cost and timeline differ significantly between routes.
Ready to take control of your weight loss journey?
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