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
What Are the Dangers and Risks of Mounjaro?
Mounjaro (tirzepatide) is a prescription-only weight loss injection licensed in the UK, but like all medications, it carries potential risks and side effects. Understanding these dangers is essential before considering treatment. This guide covers what the clinical evidence shows about Mounjaro safety, common side effects, serious risks to watch for, and how to access it safely through proper clinical assessment in the UK.
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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.
Common Side Effects and Safety Concerns
Mounjaro works as a dual GIP and GLP-1 receptor agonist, which means it activates two hormone pathways to reduce appetite and support weight loss. The most common side effects reported in clinical trials include nausea, diarrhoea, vomiting, and constipation — affecting more than 1 in 10 users. These typically occur during dose titration, when you're escalating from the starting 2.5mg dose to higher maintenance doses over several weeks.
Gastrointestinal discomfort is the primary danger users face. Indigestion, acid reflux, and stomach pain are also common. Some users experience injection site reactions (redness or bruising), fatigue, dizziness, or hair loss. The severity of side effects varies significantly between individuals — some tolerate the medication well, whilst others find gastrointestinal effects difficult to manage. Staying hydrated, eating smaller meals, and taking the injection at the same time each week may help reduce nausea. Always inform your GP or prescriber if side effects persist or worsen.
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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.
Serious Risks and When to Seek Medical Help
Serious but rare dangers require immediate medical attention. Severe stomach pain radiating to the back may indicate pancreatitis (inflammation of the pancreas) — seek emergency care if this occurs. Gallbladder problems, changes in vision (especially in people with type 2 diabetes), and serious allergic reactions (swelling of face, lips, or throat) are serious risks. Mounjaro may also cause rapid heart rate changes or complications in people with certain thyroid conditions.
Mounjaro is not suitable for everyone. You cannot take it if pregnant, breastfeeding, under 18, or allergic to tirzepatide. It requires a prescription from a UK-licensed prescriber following a clinical assessment. Your medical history, current medications, and existing health conditions will be reviewed to ensure safety. Use our free BMI calculator above to understand your current health profile, and discuss any concerns with your GP before pursuing prescription weight loss treatment.
- 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 dangerous for everyone?
Mounjaro is not dangerous for everyone, but it carries risks for certain groups. It's unsuitable if pregnant, breastfeeding, under 18, or with a history of pancreatitis or thyroid cancer. Most side effects are mild and temporary, but serious complications like pancreatitis or gallbladder problems can occur rarely. A prescriber will assess your individual safety before prescribing.
What's the difference between Mounjaro and Wegovy dangers?
Both are GLP-1-based weight loss injections with similar gastrointestinal side effects. Mounjaro is a dual GIP and GLP-1 agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Individual safety profiles and side effect severity vary by person. Neither is inherently more dangerous — your medical history determines suitability.
How do I access Mounjaro safely in the UK?
Mounjaro is prescription-only and requires clinical assessment. NHS access is through specialist tier 3 weight management services (referral from your GP), though waiting lists are long in many regions. Private access is available through online consultations with UK-licensed prescribers. Either route ensures proper medical oversight before treatment begins.
What happens if I experience severe side effects on Mounjaro?
Contact your GP or prescriber immediately if you experience severe stomach pain, persistent vomiting, vision changes, or allergic reactions. Most mild side effects improve within days or weeks. Your prescriber may adjust your dose, slow titration, or recommend stopping treatment. Never stop suddenly without professional guidance.
Can I use MyWeightCheck tools to decide if Mounjaro is right for me?
Our free BMI calculator and GLP-1 weight loss calculator can help you understand your current health profile and estimate potential outcomes with medication. However, these tools are educational only — they don't replace clinical assessment. Always consult your GP before considering prescription weight loss treatment like Mounjaro.
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.