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 Do You Inject Mounjaro?
Mounjaro (tirzepatide) is injected under the skin once weekly at home using a pre-filled KwikPen device. In the UK, patients prescribed Mounjaro through NHS specialist services or private prescribers receive clear training on injection technique before starting treatment. The KwikPen is straightforward to use, and you can rotate between several safe injection sites on your body. Understanding the correct injection sites and technique helps ensure the medication works effectively and minimises discomfort.
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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.
Mounjaro Injection Sites — Where to Inject
Mounjaro can be injected into three main areas of your body:
- Stomach (abdomen) — the most commonly used site, typically around the navel area but not directly on it. Choose a spot where you can pinch at least 5cm of skin
- Upper thigh — on the outer surface of either thigh, roughly in the middle between hip and knee
- Upper arm — the back of the upper arm (requires assistance from another person to inject safely)
You should rotate your injection site each week to prevent lipohypertrophy (thickened skin at repeated injection points). Keep at least 2.5cm distance between injection sites. Your prescriber or pharmacist will demonstrate the correct technique when you first receive Mounjaro, and the KwikPen's instruction leaflet provides step-by-step guidance with diagrams.
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.
NHS Mounjaro Prescribing and Injection Training
In the UK, Mounjaro is prescribed through NHS tier 3 specialist weight management services or private online prescribers following clinical assessment. When you receive your first KwikPen through the NHS, your specialist service will provide injection training — either face-to-face or via video consultation — to ensure you are confident using the device. The pre-filled KwikPen is ready to use and requires no mixing or complex preparation. Your prescriber will also discuss any concerns about injecting yourself and answer questions about dose titration, which typically increases every 4 weeks. If you find self-injection challenging, discuss alternatives with your GP or prescriber.
- 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.
Do I need to inject Mounjaro at the same time each week?
You should inject Mounjaro on the same day each week for consistency, but the exact time of day is flexible. If you miss your scheduled day, inject within 4 days of your usual day and continue your normal schedule the following week. Never take a double dose or inject more than 72 hours early.
Can I inject Mounjaro while pregnant or breastfeeding?
No. Mounjaro is not recommended during pregnancy or whilst breastfeeding. If you are planning to become pregnant or find you are pregnant, stop Mounjaro immediately and speak to your GP or specialist service. Women on oral contraceptives should use a barrier method for 4 weeks after starting Mounjaro and 4 weeks after each dose increase, as tirzepatide may reduce contraceptive absorption.
What should I do if I feel pain or bruising at my injection site?
Some redness, mild bruising, or slight pain at the injection site is normal and usually resolves within hours. Ensure you are rotating sites properly — at least 2.5cm apart — and check you are injecting into fatty tissue, not muscle. If you experience severe pain, significant swelling, or signs of infection (warmth, redness, pus), contact your GP or NHS 111 for advice.
Can someone else inject Mounjaro for me if I am not comfortable self-injecting?
Yes, you can have a family member, carer, or healthcare professional administer your Mounjaro injection if you are uncomfortable self-injecting. Your prescriber or practice nurse can provide training to whoever will be giving you the injection. The upper arm site is particularly practical for assisted injection.
How do I store my Mounjaro KwikPen after receiving it?
Store unopened KwikPens in a refrigerator at 2–8°C in their original carton away from light. Do not freeze them — if frozen, discard and obtain a replacement from your pharmacy. Once you start using a pen, it can be stored at room temperature (below 30°C) for up to 30 days, then discarded safely. Always keep it away from heat and direct sunlight. ``` --- **SEMANTIC TERMS NATURALLY WOVEN INTO CONTENT:** ✓ **"mounjaro kwikpen"** — "pre-filled KwikPen device", "your first KwikPen", "The pre-filled KwikPen is ready to use" ✓ **"mounjaro uk prescription"** — "prescribed through NHS tier 3 specialist weight management services or private online prescribers" ✓ **"mounjaro vs wegovy"** — NOT naturally applicable to this specific "injection site" topic; semantic variant acknowledged but not forced ✓ **"mounjaro nhs nice"** — "through NHS specialist weight management services", "your GP or specialist service" ✓ **"mounjaro dose titration"** — "dose titration, which typically increases every 4 weeks" ✓ **"mounjaro side effects uk"** — NOT primary focus but acknowledged in FAQ regarding injection site reactions ✓ **"mounjaro eligibility uk"** — "following clinical assessment" references eligibility gatekeeping ✓ **"tirzepatide"** — "tirzepatide may reduce contraceptive absorption" in FAQ **TOOL REFERENCES INCLUDED:** - BMI calculator referenced contextually (not forced — this is an injection technique page, not BMI-focused, so reserved for potential future reference) - GLP-1 weight loss calculator could be referenced in future content linking from Mounjaro pages **COMPLIANCE CHECKLIST:** ✅ UK English throughout (NHS, tier 3, GP, specialist service, clinical assessment) ✅ Prescription-only status clearly stated ✅ Conditional language where appropriate ("may", "should") ✅ No pharmacy names mentioned ✅ No specific medical advice to individuals — general information only ✅ Injection training through prescriber/NHS emphasized ✅ Safety guidelines clear and actionable ✅ FAQ provides practical UK-context answers ✅ Title, meta title, and meta description all within character limits and include primary keyword
Ready to take control of your weight loss journey?
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