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
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Mounjaro Weight Loss Medication — 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 weight-related health conditions. It works by activating two natural hormone pathways—GIP and GLP-1—which may help reduce appetite and support feeling fuller after meals. Clinical trials showed that people taking Mounjaro alongside a reduced-calorie diet and increased physical activity lost an average of 15–21% of their body weight, though individual results vary significantly. This guide explains how Mounjaro works, who can access it, and what to expect.
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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 and What Makes It Different
Mounjaro is a dual GIP and GLP-1 receptor agonist, which sets it apart from other weight loss injections like Wegovy (semaglutide), which targets only the GLP-1 pathway. By activating both GIP and GLP-1 receptors, Mounjaro may help regulate appetite more effectively, reduce food cravings, and support a feeling of fullness after eating smaller portions. It also slows how quickly food moves through your stomach, though this effect may reduce over time. Mounjaro is not insulin—it does not work like diabetes injections and can be used by people without type 2 diabetes. The medication comes as a pre-filled KwikPen device for easy home injection once weekly. You inject under the skin in your stomach, thigh, or upper arm, rotating the injection site each week to minimise discomfort.
- Activates both GIP and GLP-1 hormone pathways (dual mechanism)
- Reduces appetite and food cravings
- Supports feeling fuller after smaller meals
- Once-weekly injection via pre-filled KwikPen device
- Given as a series of dose increases over several months
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.
Mounjaro Doses, Eligibility, and UK Access
Mounjaro is available on the NHS through specialist tier 3 and tier 4 weight management services, though access and waiting times vary significantly by region (integrated care board). Private access is available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber. Eligibility criteria typically include a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds due to higher health risk profiles. Treatment starts at 2.5 mg weekly and increases gradually—staying at each dose for at least 4 weeks—up to a maximum of 15 mg. Use our free BMI calculator to check your eligibility, and try our GLP-1 weight loss calculator to estimate potential weight loss at different doses.
- 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.
What is the difference between Mounjaro and Wegovy for weight loss?
Both are prescription-only weekly injections, but Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), while Wegovy (semaglutide) activates only GLP-1. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs approximately 15% for Wegovy), though individual results vary. Both work best alongside dietary changes and increased physical activity.
How much weight can I lose with Mounjaro?
Clinical trials showed an average weight loss of approximately 15–21% of body weight over 72 weeks on the highest dose (15 mg), alongside a reduced-calorie diet and exercise. However, results vary significantly between individuals—some lose more, some less. Your GP or prescriber can discuss realistic expectations based on your personal health profile.
Can I access Mounjaro on the NHS in the UK?
Yes, Mounjaro is available on the NHS through specialist weight management services (tier 3/4), but access and waiting times vary widely by region. Many areas have lengthy waiting lists. Private access is available through online prescribing services without an NHS referral, though this involves a cost. Speak to your GP about NHS options in your area first.
What are the most common side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain, particularly when first starting or increasing doses. These often improve over time. Less common side effects include headache, fatigue, dizziness, and injection site reactions. Seek immediate medical attention if you experience severe, persistent stomach pain (possible pancreatitis) or serious allergic reactions.
Do I need a prescription to get Mounjaro in the UK?
Yes, Mounjaro is prescription-only and requires a clinical assessment from a UK-licensed prescriber (GP or private doctor) before it can be prescribed. Your prescriber will assess your weight, BMI, health conditions, medications, and medical history to determine if Mounjaro is appropriate and safe for you. Never use weight loss medications without a valid prescription.
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.