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 The Mounjaro Jab Safe?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed for use in the UK and approved by the MHRA. Like all medications, it has potential side effects — but clinical trial data supports its safety profile when used as prescribed under medical supervision. The key to safe use is understanding what to expect, recognising warning signs, and working with a licensed prescriber throughout your treatment.
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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.
What the Clinical Evidence Shows
Mounjaro's safety profile comes from the SURMOUNT clinical trial programme, which involved thousands of participants over 72 weeks. The most common side effects are gastrointestinal — nausea, diarrhoea, vomiting, and constipation — which typically occur during dose escalation and often improve with time. Serious adverse events in clinical trials were rare. The MHRA continues to monitor Mounjaro closely (it carries a Black Triangle ▼ status, meaning additional monitoring occurs). Your prescriber will assess your individual health before recommending treatment and adjust your dose based on how well you tolerate it. Using our GLP-1 weight loss calculator can help you understand potential outcomes alongside your prescriber's guidance.
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.
Important Safety Considerations and When to Seek Help
Mounjaro is not suitable for everyone. You cannot take it if you're pregnant, breastfeeding, under 18, or have a personal or family history of medullary thyroid cancer. If you take other medications — especially oral contraceptives, diabetes medications, or blood pressure drugs — inform your prescriber, as Mounjaro may affect how they work. Seek urgent medical attention if you experience severe, persistent stomach pain (possible pancreatitis), serious allergic reactions, gallbladder problems, or changes in vision. Minor side effects like nausea usually settle; if they persist or worsen, contact your prescriber. Your GP or licensed prescriber can discuss whether Mounjaro is right for your 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?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are licensed UK weight management medications with established safety profiles. Mounjaro uses a dual GIP and GLP-1 mechanism; Wegovy uses GLP-1 alone. Safety outcomes in clinical trials are comparable, though individual responses vary. Your prescriber will recommend the most appropriate option for your health.
Can I use Mounjaro if I'm on other medications?
Mounjaro can interact with some medications, particularly oral contraceptives and diabetes drugs. Inform your prescriber of all medications you take before starting. They will assess compatibility and adjust doses if needed. Never start Mounjaro without discussing your full medication list.
What if I experience severe nausea on Mounjaro?
Nausea is common during dose escalation and often improves within days or weeks. Eating smaller, simpler meals may help. However, if nausea is severe or persistent, contact your prescriber — they may slow your dose escalation or recommend alternatives. Don't stop taking Mounjaro without medical guidance.
Is the Mounjaro KwikPen safe to use at home?
Yes, the Mounjaro KwikPen is designed for self-injection at home. Your prescriber or pharmacist will provide injection training. Store unopened pens in the fridge (2–8°C) and opened pens at room temperature for up to 30 days. Rotate injection sites weekly to reduce irritation.
What makes Mounjaro a Black Triangle medication?
The Black Triangle ▼ symbol means the MHRA is monitoring Mounjaro closely for new safety information. This is standard for newer medications and reflects rigorous oversight, not increased danger. It allows regulators to quickly identify and act on any emerging safety signals from real-world use. ```
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.