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?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK, and like all medicines, it carries potential risks alongside benefits. The question "Is Mounjaro dangerous?" needs nuance โ it's not inherently dangerous for most people, but it requires proper medical assessment, is not suitable for everyone, and does cause side effects. This guide explains the safety profile, who should and shouldn't use it, and what to watch for. Your GP or prescriber will assess whether Mounjaro is appropriate for your individual health.
10,000+ calculations today ยท NHS-aligned thresholds ยท 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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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.
Mounjaro Safety Profile and Known Risks
Mounjaro is a prescription-only medicine, meaning it should only be used under medical supervision. Like all medications, it has potential side effects and contraindications. Clinical trial data (SURMOUNT-1) shows Mounjaro is generally well-tolerated, but understanding the risks is essential.
Most common side effects:
- Nausea (very common, especially at dose initiation)
- Diarrhoea and constipation
- Stomach pain and indigestion
- Vomiting (usually mild)
- Injection site reactions
- Fatigue and dizziness
- Hair loss (reported in some users)
These side effects often improve as your body adjusts. However, if you experience severe, persistent stomach pain spreading to your back, seek immediate medical attention โ this could indicate pancreatitis, a serious condition.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care โ 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 โ 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 โ completely free.
Who Should NOT Take Mounjaro
Mounjaro is contraindicated (unsafe) for certain groups:
- Under 18 years of age
- Pregnant or planning pregnancy โ tirzepatide may harm fetal development
- Breastfeeding
- Allergy to tirzepatide or any ingredients
- Personal or family history of medullary thyroid cancer
- Multiple Endocrine Neoplasia (MEN) type 2
- Severe gastroparesis or digestion problems
- Recent pancreatitis
If you have type 2 diabetes, you may need insulin or sulphonylurea dose adjustments when starting Mounjaro โ your prescriber will manage this. Use our free GLP-1 weight loss calculator to explore projected outcomes, but always discuss safety concerns with your GP before starting any medication.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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.
Can Mounjaro cause pancreatitis?
Pancreatitis (pancreas inflammation) is a rare but serious risk with GLP-1 and GIP receptor agonists. Seek immediate medical attention if you experience severe upper stomach pain, back pain, or persistent vomiting. Your prescriber screens for pancreatitis risk before starting treatment. Contact your GP or NHS 111 immediately if symptoms occur.
Is Mounjaro safer than Wegovy?
Both Mounjaro and Wegovy are licensed in the UK and have similar safety profiles. Mounjaro uses a dual GIP+GLP-1 mechanism whereas Wegovy is GLP-1 only. Clinical trials show both are well-tolerated in appropriate candidates. Safety depends on individual health factors, not the medication choice. Your prescriber will advise which is safer for you.
What happens if I stop Mounjaro suddenly?
Stopping Mounjaro doesn't cause physical withdrawal, but weight may return relatively quickly if diet and exercise don't continue. There's no medical danger in stopping, but do not stop abruptly without consulting your prescriber โ they may recommend tapering the dose. Rebound weight gain is common when any weight loss medication is discontinued.
Can Mounjaro affect my other medications?
Yes. Mounjaro slows gastric emptying, which may reduce absorption of oral medications. Oral contraceptives are specifically affected โ women should use a barrier method for 4 weeks after starting and after each dose increase. Inform your prescriber of all medications. Diabetes medication doses may need adjustment.
Does Mounjaro cause thyroid cancer?
Mounjaro labelling includes a warning about thyroid cancer based on animal studies, not human cases. No thyroid cancer has been confirmed in clinical trials. However, if you have a personal or family history of medullary thyroid cancer, or MEN type 2, Mounjaro is contraindicated. Discuss any thyroid concerns with your GP before starting.
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.