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
Mounjaro Fat Loss Injections — What You Need to Know
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection licensed in the UK for adults with obesity or overweight with health conditions. It works by activating two natural hormone pathways (GIP and GLP-1) to help regulate appetite and support feeling fuller after meals. Results vary between individuals, and the medication is used alongside diet and physical activity changes. Access is available through NHS specialist weight management services or private online prescribing following a clinical assessment.
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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.
How Mounjaro Works for Fat Loss
Mounjaro's dual GIP and GLP-1 receptor agonist mechanism sets it apart from other weekly weight loss injections. It mimics natural hormones that regulate appetite, reduce food cravings, and slow how quickly food leaves the stomach. This combination helps many people eat smaller portions and feel satisfied for longer.
In the SURMOUNT-1 clinical trial, participants using Mounjaro at the maximum 15 mg dose lost an average of approximately 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity. At 10 mg, average loss was around 19.5%. Results vary significantly between individuals — some lose more, some less.
The medication comes as a KwikPen pre-filled injection device, used once weekly. Doses start at 2.5 mg and increase gradually over weeks, with a maximum of 15 mg weekly. Your prescriber will adjust your dose based on your response and tolerance.
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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.
Eligibility, Side Effects, and UK Access
UK eligibility: Adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease, sleep apnoea), may be eligible. Lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults.
Common side effects include nausea, diarrhoea, constipation, and stomach pain — often mild and reduce over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions.
NHS access is through tier 3 specialist weight management services via GP referral, though waiting lists vary by region. Private access is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber — no NHS referral needed.
- 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 Wegovy?
No. Mounjaro (tirzepatide) and Wegovy (semaglutide) are different medications. Mounjaro activates two hormone pathways (GIP and GLP-1), while Wegovy activates only GLP-1. Both are prescription-only weekly injections licensed for weight management in the UK. Clinical trials showed similar average weight loss, but individual results vary. Your prescriber will help determine which is more suitable.
How quickly will I lose weight with Mounjaro?
This varies. The NHS recommends sustainable weight loss of around 0.5–1 kg per week. Clinical trials showed average loss of 15–21% of body weight over 72 weeks, but individual results depend on dose, diet, activity level, metabolism, and other factors. Your GP or prescriber can discuss realistic timelines for your situation.
Can I get Mounjaro on the NHS?
Yes, Mounjaro is approved by NICE for use in NHS specialist weight management services (tier 3). However, availability varies significantly by region and NHS waiting lists can be long. Ask your GP about referral options. Private prescribing is also available through UK online services, typically faster but at a cost.
What are the most common Mounjaro side effects?
Nausea, diarrhoea, constipation, and stomach pain are very common, especially when starting or increasing doses. These often improve over time as your body adjusts. Serious side effects are rare but include severe stomach pain (possible pancreatitis), gallbladder problems, and allergic reactions. Always report unexpected symptoms to your prescriber immediately.
How do I track progress with Mounjaro?
Monitor your weight regularly using consistent scales (same time, same day). Track your BMI using our free BMI calculator to see how it changes alongside treatment. Our free progress tracker lets you log weekly weight, measurements, and how you feel — this helps identify patterns and shows progress beyond the scales. Share results with your prescriber at follow-up appointments.
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.