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 Mounjaro Slimming Injections?
Mounjaro is a prescription-only weight management injection licensed in the UK for adults with obesity or excess weight and related health conditions. The active ingredient is tirzepatide, a dual GIP and GLP-1 receptor agonist that works differently from other slimming injections. It's administered as a once-weekly injection and may help reduce appetite and support weight loss alongside diet and physical activity. Use our free BMI calculator above to check if you might be eligible, and our GLP-1 weight loss calculator to explore potential outcomes at different doses.
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.
How Does Mounjaro Work as a Slimming Injection?
Mounjaro activates two natural hormone pathways in your body: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism sets it apart from single-action weight loss injections like Wegovy, which only targets GLP-1. The medication helps regulate appetite signals in the brain, which may reduce cravings and help you feel fuller after eating smaller portions. It also slows how quickly food moves through your stomach. In the SURMOUNT-1 clinical trial, participants using Mounjaro alongside a reduced-calorie diet lost an average of 15–21% of their body weight over 72 weeks — though individual results vary significantly. Mounjaro is delivered via a pre-filled KwikPen device, making injections simple to self-administer at home each week.
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.
UK Eligibility and How to Access Mounjaro
In the UK, Mounjaro may be prescribed if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may be eligible at lower BMI thresholds (27.5+) due to higher health risks at lower weights. You can access Mounjaro through NHS specialist weight management services (tier 3) or via private online prescribing following a clinical assessment. NHS access varies by region and often involves waiting lists. A prescriber will assess whether Mounjaro is suitable for your individual health, medications, and circumstances.
- 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 the same as Ozempic?
No. Both contain semaglutide, but Ozempic is licensed only for type 2 diabetes (doses up to 2mg) — using it for weight loss is off-label. Mounjaro (tirzepatide) is the UK-licensed weight management option and uses a different mechanism with dual GIP and GLP-1 activation.
What are the main side effects of Mounjaro slimming injections?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain. Most side effects are mild and often improve over time as your body adjusts. Serious side effects are rare but seek immediate medical attention for severe stomach pain or allergic reactions.
How much weight can I expect to lose with Mounjaro?
Clinical trials showed an average loss of 15–21% of body weight over 72 weeks alongside diet and activity changes. However, individual results vary significantly — some people lose more, some less. Your progress depends on adherence, lifestyle changes, and individual metabolism.
Can I get Mounjaro through the NHS?
Yes, NHS specialist weight management services (tier 3) can prescribe Mounjaro. However, access is limited and waiting lists are often long. Private online prescribing is also available following a clinical assessment. Your GP can discuss options with you.
What's the difference between Mounjaro and Wegovy?
Mounjaro uses dual GIP and GLP-1 activation; Wegovy uses GLP-1 only. Clinical trials suggest Mounjaro may achieve slightly higher average weight loss. Both are once-weekly injections. Your prescriber will recommend the most suitable option based on your health profile.
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.