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
Is Mounjaro Dangerous? Safety Comparison with Wegovy
Neither Mounjaro nor Wegovy is inherently "dangerous" when prescribed appropriately, but both are prescription-only medications with side effects that require clinical assessment. Mounjaro (tirzepatide) and Wegovy (semaglutide) work differently and have slightly different safety profiles based on clinical trial data. This guide compares the safety evidence for both medications to help you understand what prescribers consider when deciding which is suitable for you.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Safety Data: Mounjaro vs Wegovy
Both Mounjaro and Wegovy have undergone rigorous UK and international clinical trials. Mounjaro (tirzepatide) was evaluated in the SURMOUNT trials, whilst Wegovy (semaglutide) was evaluated in the STEP trials. The most common side effects in both trials were gastrointestinal — nausea, diarrhoea, vomiting, and constipation — which typically diminish as the body adjusts to the medication.
In SURMOUNT-1, serious adverse events were rare but included pancreatitis and gallbladder problems. Similarly, STEP trials reported low rates of serious side effects. Both medications require dose titration (gradual increase from a starting dose), which helps minimise side effects. The UK MHRA approved both medications after evaluating safety data, and both carry the same key contraindications: pregnancy, personal or family history of medullary thyroid cancer, and multiple endocrine neoplasia syndrome type 2 (MEN2).
Key difference: Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 agonist only. This dual mechanism may affect how individuals respond and tolerate the medication, but clinical data does not show one is definitively safer than the other — individual suitability varies.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Might Be Right for You?
Safety is only one factor prescribers consider. Your GP or licensed prescriber will assess your full medical history, current medications, and health conditions before recommending Mounjaro or Wegovy. Neither medication is automatically "safer" — it depends on your individual circumstances. Someone with a history of pancreatitis, for example, would require careful assessment before either medication. Someone taking certain diabetes medications may need dose adjustments with either drug.
Both Mounjaro and Wegovy require a UK prescription following clinical assessment — you cannot self-prescribe based on safety reputation alone. Access via NHS specialist weight management services or private online prescribing both involve proper clinical review. If you are considering either medication, use our free GLP-1 weight loss calculator above to understand potential outcomes, then discuss suitability with your prescriber based on your personal health profile.
- 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 Mounjaro safer than Wegovy?
Neither medication is inherently safer — both underwent rigorous clinical trials and have similar safety profiles. Serious side effects are rare with both. Safety depends on your individual health, medications, and medical history. Your prescriber will assess which is more suitable for you specifically.
What are the most common side effects of both medications?
The most common side effects are gastrointestinal: nausea, diarrhoea, vomiting, and constipation. These typically occur in the first weeks and often improve as your body adjusts. Both medications use gradual dose titration to minimise side effects. Serious side effects like pancreatitis are rare.
Can I choose between Mounjaro and Wegovy myself?
No — both are prescription-only medications. Your GP or licensed prescriber will recommend the most suitable option after clinical assessment. You cannot self-prescribe either medication, and choice depends on your health profile, not personal preference alone.
What does "dual GIP and GLP-1 agonist" mean for Mounjaro safety?
Mounjaro activates two hormone pathways (GIP and GLP-1) instead of one (GLP-1 only in Wegovy). This dual action may affect how the medication works in your body, but clinical data does not show it is safer or more dangerous — it simply means individual responses may vary.
Are both medications suitable if I have type 2 diabetes?
Mounjaro and Wegovy are both licensed for weight management in adults with or without diabetes. However, if you take insulin or sulphonylureas, your prescriber may need to adjust your diabetes medication doses because GLP-1 medications affect blood sugar. Always inform your prescriber of all current medications.
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.