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
How Mounjaro Supports Weight Loss
Mounjaro (tirzepatide) is a prescription-only, once-weekly weight loss injection licensed in the UK for adults with obesity or overweight with related health conditions. It works as a dual GIP and GLP-1 receptor agonist—a mechanism that may help regulate appetite, reduce food cravings, and support feeling fuller after meals. Unlike many other weight loss approaches, Mounjaro combines two natural hormone pathways to help your body manage weight more effectively. This guide explains how it works, what results you might expect, and how to access it in the UK.
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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.
How Mounjaro Works and What Results Show
Mounjaro activates two hormone receptors—GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1)—which work together to regulate appetite and food intake. This dual action is what distinguishes Mounjaro from single-mechanism GLP-1 receptor agonists like Wegovy (semaglutide). The medication slows how quickly food leaves your stomach, signals fullness to your brain, and helps your body utilise fat more effectively.
In the SURMOUNT-1 clinical trial, adults 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. Results at the 10 mg dose averaged around clinically studied weight loss. However, individual results vary significantly, and weight loss is not assured. Our GLP-1 weight loss calculator can help you estimate potential weight loss at different doses based on your current weight.
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
You may be eligible for Mounjaro in the UK if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease). Lower BMI thresholds apply if you are of South Asian, Chinese, Black African, or Black Caribbean heritage, reflecting higher health risks at lower weights in these populations.
You can access Mounjaro through NHS specialist weight management services (tier 3) following a GP referral, though waiting lists vary by region. Private access is available through UK-licensed prescribers via online consultation and GPhC-registered pharmacies. Whichever route you choose, a prescriber will assess whether Mounjaro is clinically appropriate for you. Use our free BMI calculator above to check your starting BMI—this is the first step in determining eligibility.
- 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.
How long does it take to see weight loss results with Mounjaro?
Most people start noticing appetite changes within 1–2 weeks of starting the lowest dose (2.5 mg), though initial weight loss is typically modest. Significant weight loss becomes more apparent after 8–12 weeks as doses are gradually increased. The SURMOUNT trials measured results over 72 weeks, so consistent use over several months is important. Your progress tracker can help you log weekly weigh-ins to monitor your personal journey.
Is Mounjaro the same as a slimming injection or weight loss jab?
Yes—Mounjaro is one of the prescription weight loss injections available in the UK, commonly referred to as "slimming jabs" or "weight loss injections." It's a prescription-only medicine, not a cosmetic injection, and requires a clinical assessment before prescribing. Other licensed options include Wegovy (semaglutide) and Saxenda (liraglutide), each with different mechanisms and dosing schedules.
What is the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 receptor agonist only. In clinical trials, Mounjaro showed slightly higher average weight loss (~21% at maximum dose) compared to Wegovy (~15%), but individual results vary. Both are once-weekly injections, prescription-only, and work best alongside diet and exercise changes.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved for NHS prescription through specialist tier 3 weight management services. Access requires a GP referral and varies significantly by region and ICB (Integrated Care Board). NHS waiting lists can be lengthy in many areas. Private prescription is also available through online prescribers if you meet eligibility criteria, though costs apply.
What side effects should I expect with Mounjaro?
Very common side effects include nausea, diarrhoea, constipation, and stomach pain—usually mild and reducing over time. Common side effects include indigestion, fatigue, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always inform your prescriber of any concerns, and seek urgent medical attention if you experience severe or persistent symptoms.
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.