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 Can I Inject Mounjaro — UK Injection Site Guide
Mounjaro (tirzepatide) is injected under the skin once weekly, and you can rotate between three main injection sites on your body. The most common areas are your stomach (abdomen), upper thigh, or upper arm — each location works equally well for absorption. This guide explains the approved injection sites for Mounjaro in the UK, how to rotate between them safely, and how this compares to Wegovy injection sites. Always follow your prescriber's instructions, as they will provide specific training during your initial consultation.
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.
Mounjaro and Wegovy Injection Sites — What's the Same, What's Different
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) use identical approved injection sites:
- Stomach (abdomen) — the most commonly used site; inject into fatty tissue at least 5cm away from the belly button
- Upper thigh — front or outer surface; easy to self-inject, commonly rotated with stomach injections
- Upper arm — outer back area; usually requires assistance from a partner or healthcare professional to inject safely
The key difference is not where you inject, but the injection frequency and device. Mounjaro uses a pre-filled KwikPen and is injected once weekly. Wegovy also uses a pre-filled auto-injection pen and is given once weekly. Both require rotating your injection site each week to avoid skin irritation, lipohypertrophy (thickened fatty tissue), or injection site reactions. Your prescriber will demonstrate the correct injection technique during your first appointment. Never inject into the same spot twice in a row — vary your sites in a planned pattern, such as alternating between stomach, left thigh, right thigh, and upper arm weekly.
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.
Why Injection Site Rotation Matters — Individual Suitability & Prescriber Guidance
Rotating your injection site reduces the risk of skin problems including bruising, redness, lumps, and local reactions. It also ensures consistent medication absorption across different body areas. When deciding between Mounjaro and Wegovy, injection site location is not a deciding factor — both medications are injected into the same areas using the same technique. Your prescriber will assess which medication is more suitable based on your individual health profile, eligibility criteria, and response to similar treatments. Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy works through GLP-1 alone; clinical trial data shows both medications support weight loss when combined with diet and exercise changes, though individual results vary significantly. Your GP or prescriber will help determine the right choice for you following a full clinical assessment.
- 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 in the same spot every week?
No. You should rotate your injection site each week to different locations (stomach, thigh, arm) or different areas within the same location. Injecting in the same spot repeatedly increases risk of skin irritation, bruising, lipohypertrophy, and reduced medication absorption. Your prescriber will show you a rotation pattern to follow.
Is Mounjaro injected the same way as Wegovy?
Yes, both use pre-filled injection pens and are given once weekly into the same three approved sites (stomach, thigh, upper arm). The injection technique is identical. The main difference is the medication mechanism — Mounjaro is a dual GIP+GLP-1 agonist, Wegovy is a GLP-1 agonist only — but both are injected subcutaneously (under the skin) using the same body areas.
What should I do if I get redness or bruising at my injection site?
Minor redness or bruising usually resolves within a few days and is normal. Continue rotating sites as advised. If you experience severe pain, significant swelling, infection signs (warmth, pus), or persistent lumps, contact your GP or prescriber. These may indicate a need to adjust your injection technique or site rotation pattern.
Can I inject Mounjaro through clothing?
No. Always inject into clean, dry skin. Remove or lift your clothing to expose the injection site fully. Injecting through fabric risks infection and inaccurate dosing. Your KwikPen needle is designed to penetrate skin — fabric may block proper needle insertion.
How do I choose between Mounjaro and Wegovy if I'm worried about injections?
Both require weekly injections, so injection concerns apply equally. What differs is the medication itself — Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist with average weight loss of 15–21% in trials, whilst Wegovy (semaglutide) is GLP-1 only with average weight loss around 15%. Your prescriber will recommend the most suitable option based on your health profile, not injection anxiety. Both use simple, easy-to-use pre-filled pens designed for patient self-injection.
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.