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
Where to Inject Mounjaro in Your Stomach
If you've been prescribed Mounjaro (tirzepatide) as a weekly weight loss injection, understanding proper injection sites is essential for safe and effective treatment. Your stomach (abdomen) is the most common injection site for this prescription-only medicine, though there are other approved areas on your body. This guide explains exactly where to inject, how to rotate sites correctly, and what to expect when administering your weekly KwikPen. Always follow your prescriber's specific instructions, and ask your healthcare professional if you have any concerns about injection technique.
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.
Approved Mounjaro Injection Sites and Stomach Area Guidance
Mounjaro is administered as a once-weekly injection using a pre-filled KwikPen. The stomach (abdomen) is the preferred injection site for most patients. This area is favoured because it has good subcutaneous tissue (fat layer) and is easy to access and visualise yourself.
- Stomach area: Inject into the fatty tissue of your abdomen, at least 5 cm (about 2 inches) away from your belly button. Avoid the area directly over your navel. The lower abdomen, sides, or upper abdomen are all suitable.
- Upper thigh: The outer thigh can be used, though less commonly for self-injection.
- Upper arm: The back of your upper arm is an approved site, but typically requires assistance from another person.
Before injecting, clean the skin with an alcohol wipe and allow it to dry completely. This helps prevent infection at the injection site. Never inject into areas where you have redness, bruising, hardness, or dimples from previous injections—these signs indicate lipohypertrophy (thickened fat tissue).
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.
Site Rotation — Why It Matters for Safe Treatment
Site rotation is crucial when using any weekly injection medicine. Using the same exact spot repeatedly can cause lipohypertrophy, skin thinning, or reduced absorption of the medication. Rotate your injection site each week within the same general area (e.g. stomach) or alternate between different areas (stomach one week, thigh the next).
A simple rotation pattern: Week 1 lower abdomen, Week 2 upper abdomen, Week 3 right side, Week 4 left side—then repeat. Always space injections at least 2–3 cm apart from previous sites. If you notice any hardening, numbness, or discolouration at your injection sites, stop injecting there and discuss with your GP or prescriber. Proper site rotation helps maintain consistent drug absorption and reduces injection site reactions, supporting better outcomes alongside your reduced-calorie diet and increased physical activity.
- 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.
Can I inject Mounjaro anywhere on my stomach?
You should inject into fatty tissue areas of your abdomen, at least 5 cm away from your belly button. Avoid areas with existing bruises, redness, or thickened tissue. Both the lower and upper abdomen are suitable, and rotating between these areas each week is recommended to prevent tissue damage.
What happens if I inject Mounjaro into muscle instead of fat?
Mounjaro is designed as a subcutaneous injection, meaning it goes into the fatty tissue layer under your skin. Injecting into muscle may cause pain, bruising, or reduced medication absorption. If you're unsure about injection technique, ask your prescriber or nurse for a demonstration before self-injecting.
Is it normal to have bruising or redness after a Mounjaro injection?
Minor redness or slight bruising at the injection site is common and usually resolves within a few hours or days. However, if you experience severe pain, large bruises, swelling, or signs of infection (warmth, pus), contact your GP. These could indicate an injection site reaction or infection requiring medical attention.
How do I know if I have lipohypertrophy from Mounjaro injections?
Lipohypertrophy appears as thickened, hardened, or lumpy tissue at injection sites. You might notice dimples, bumps, or areas that feel different to touch. If you develop this, stop injecting into that area and inform your prescriber. Using a consistent site rotation pattern helps prevent this complication.
Can I use the same injection site twice in one month?
No—proper rotation is essential. Space injections at least 2–3 cm apart and avoid the same spot for at least 3–4 weeks. This practice reduces lipohypertrophy risk and ensures consistent medication absorption. A weekly rotation between different stomach areas is a safe, simple approach.
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.