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 Is a Monjaro Shot?
A Monjaro shot is a once-weekly injection containing tirzepatide, a prescription-only weight loss medication licensed in the UK. It works as a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways to help regulate appetite and support feeling fuller after meals. Monjaro is administered using a pre-filled KwikPen device and may help adults with excess weight lose weight when combined with dietary changes and increased physical activity. Individual results vary, and a clinical assessment is required before prescription.
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 the Monjaro Shot Work?
Monjaro (tirzepatide) works differently from other weight loss injections because it targets two natural hormone systems simultaneously. The GIP receptor helps regulate how your body uses glucose and fat, while the GLP-1 receptor agonist component signals to your brain that you're full, reducing appetite and food cravings.
- Slows how quickly food leaves your stomach, helping you feel satisfied longer
- Reduces hunger signals in the brain
- May help regulate blood sugar levels
- Supports fat utilisation by the body
The effects of slowed gastric emptying typically reduce over time as your body adapts. Clinical trials showed that participants taking Monjaro lost an average of 15–21% of their body weight over 72 weeks, though results vary significantly between individuals. You can use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
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.
Monjaro Shot Doses and Administration
Monjaro shots start at 2.5 mg weekly and increase gradually, with a minimum of four weeks at each dose level before escalation. The maximum dose is 15 mg once weekly. Each KwikPen contains four pre-filled doses (one month's supply) and is injected into your stomach, thigh, or upper arm.
- Store unopened pens in a fridge (2–8°C) until use
- After first use, pens can be kept at room temperature for up to 30 days
- Rotate injection sites each week to prevent skin irritation
- If you miss a dose, inject within 4 days of the missed date or skip to your next scheduled dose
Your prescriber will guide you through the correct injection technique and help determine the right dose for your needs based on your individual response and health goals.
- 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 Monjaro shot the same as Ozempic?
No. Ozempic contains semaglutide and is licensed for type 2 diabetes (not weight loss in the UK). Monjaro contains tirzepatide and is specifically licensed for weight management. Both are GLP-1-related but have different mechanisms and approved uses.
Do you need a prescription for Monjaro shots?
Yes. Monjaro is prescription-only and requires a clinical assessment before being prescribed. In the UK, you can access it through NHS specialist weight management services or via private online prescribing through a UK-licensed prescriber.
How much weight can you lose with Monjaro shots?
Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks, but individual results vary significantly. Weight loss depends on dose, diet, physical activity, and personal factors. Use our free weight loss calculator to estimate potential outcomes.
What are the main side effects of Monjaro shots?
Common side effects include nausea, diarrhoea, constipation, and stomach pain. These often improve over time. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or allergic reactions. Always report side effects to your prescriber.
Can you get Monjaro on the NHS in the UK?
NICE has approved tirzepatide (Monjaro) for NHS use, but access is through specialist tier 3 weight management services. You'll need a referral from your GP. Availability and waiting times vary significantly by region. Private access is available through online prescribing services.
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.