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
Free tracker included with every download this week
Long-Term Side Effects: Mounjaro vs Wegovy
Long-term side effects differ between Mounjaro and Wegovy because they work through different mechanisms. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) activates only the GLP-1 pathway. Clinical trial data shows both medications are generally well-tolerated over 52+ weeks, though individual experiences vary. Understanding these differences helps inform discussions with your GP or prescriber about which medication might suit your health profile. Our free GLP-1 weight loss calculator can help you explore potential outcomes with either medication.
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Calculate Your BMI Instantly
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.
Clinical Trial Data: Long-Term Safety Profiles
The SURMOUNT-4 trial followed Mounjaro users for up to 104 weeks, showing that gastrointestinal side effects (nausea, diarrhoea, constipation) were most common during dose titration phases but often improved as the body adapted. By week 52, most tolerability issues had settled for many participants. The STEP-4 trial evaluated Wegovy (semaglutide) similarly, with comparable gastrointestinal patterns during the initial 0.25mg to 2.4mg titration schedule.
- Mounjaro: Nausea peaked at weeks 1–8, then decreased. Hair loss (alopecia) was reported by up to 3% of users.
- Wegovy: Similar nausea pattern during dose escalation. Hair loss less frequently reported than Mounjaro in trial data.
- Both medications: Injection site reactions were generally mild and temporary. Serious pancreatitis was rare.
Long-term discontinuation rates due to side effects were approximately 3–5% for both medications, suggesting most users who continue treatment do so without intolerable adverse effects.
Clinically BackedWeight Loss
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Which Medication Suits You? Individual Assessment
Both Mounjaro and Wegovy are prescription-only medicines and require a clinical assessment before being prescribed. Your GP or a licensed prescriber will evaluate your personal health history, existing medications, and gastrointestinal tolerance to recommend the most suitable option.
Key factors your prescriber considers:
- Previous experience with GLP-1 medications (e.g., Saxenda)
- History of pancreatitis, gallbladder disease, or severe gastroparesis
- Current medications that may interact with dose titration
- Type 2 diabetes status (affects suitability assessment)
- Your preference regarding once-weekly vs once-daily dosing
Neither medication is inherently "safer" long-term — suitability depends entirely on your individual clinical profile. Use our BMI calculator to check your eligibility category, then discuss findings with your healthcare provider.
- 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.
Are long-term side effects worse with Mounjaro than Wegovy?
Clinical trials show comparable long-term side effect profiles. Both cause similar gastrointestinal effects during dose titration, with improvement by week 12–16. Mounjaro users reported slightly higher hair loss rates in trials, but serious adverse events were rare with both medications. Individual experiences vary considerably.
How long do Mounjaro side effects typically last?
Most gastrointestinal side effects peak during the first 4–8 weeks and improve by week 12 as the body adjusts. Nausea and appetite suppression often stabilise once you reach your maintenance dose. If side effects persist beyond 16 weeks, discuss with your prescriber about dose adjustment.
Can you stop Mounjaro if long-term side effects develop?
Yes. If you experience unmanageable side effects, your GP can stop the medication. Some people switch to Wegovy (different mechanism, may be tolerated better) or discontinue weight loss injections entirely. Always discuss with your prescriber before stopping — stopping suddenly may cause rebound hunger.
Which is safer long-term — Mounjaro or Wegovy?
Both are UK-licensed and considered safe for long-term use when prescribed appropriately. "Safer" depends on your individual health factors. Your GP will assess which medication aligns with your medical history, existing conditions, and risk tolerance. Neither has clear long-term safety superiority.
Do long-term side effects improve the longer you take Mounjaro or Wegovy?
For most users, yes. Gastrointestinal side effects typically improve after the first 12–16 weeks as your body adapts to the medication. Hair loss (if it occurs) is usually temporary. However, some people experience persistent mild symptoms. Track symptoms using our free progress tracker alongside your weight.
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.