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
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Where's best to inject Mounjaro?
Mounjaro (tirzepatide) is a once-weekly injectable medication prescribed in the UK for weight management. You'll need to know the correct injection sites before starting treatment. The abdomen, upper thigh, and upper arm are all suitable locations, and rotating between sites each week helps prevent skin irritation. This guide explains the approved injection sites, how to rotate safely, and how to access Mounjaro through NHS or private prescription in the UK.
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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 rotation
Stomach (abdomen) is the most common injection site for Mounjaro. Inject into the fatty tissue around the navel, avoiding the area within 5cm of your belly button. Upper thigh is the second most popular site — inject into the outer area of your thigh, roughly midway between hip and knee. Upper arm is also approved but typically requires assistance from another person to inject safely into the back of your arm.
- Rotate injection sites each week to prevent lipodystrophy (skin thickening or dimpling)
- Avoid injecting into areas with bruising, scarring, or active inflammation
- Allow at least 2–3cm between injection sites if using the same area
- Keep skin clean and dry before injecting
- Room temperature skin is easier to inject than cold skin
Each Mounjaro KwikPen delivers a pre-filled dose. The needle is typically 4–6mm long and relatively thin, making injection less painful than many people expect. Always follow your prescriber's or pharmacist's guidance on injection technique.
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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.
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Accessing Mounjaro in the UK: NHS vs private prescription
NHS access: Mounjaro (tirzepatide) is available through specialist tier 3/4 weight management services via NHS referral. Your GP can refer you, though waiting lists vary significantly by region and can extend several months to years depending on local availability. NICE has approved tirzepatide for NHS use in eligible adults with BMI ≥30 or BMI 27–29.9 with weight-related health conditions.
Private access: Licensed UK prescribers offer online consultations without NHS referral. Following assessment, prescriptions are dispensed by GPhC-registered pharmacies. Costs typically range from £130–£320 monthly depending on dose. Both routes require a clinical assessment to confirm Mounjaro is suitable for you. Use our GLP-1 weight loss calculator to explore potential outcomes with different doses.
Q1: Can I inject Mounjaro into the same site twice? A1: No — rotate injection sites each week. Using the same site repeatedly increases risk of lipodystrophy (thickening or denting of skin tissue). If you need to use the same general area (e.g., stomach), space injections at least 2–3cm apart and avoid that spot for at least 4 weeks before returning. Q2: Is Mounjaro injection painful? A2: Most users report minimal discomfort. The needle is very thin (typically 4–6mm) and the pre-filled KwikPen is designed for ease of use. Pain sensitivity varies individually. Injecting into room-temperature skin may feel less uncomfortable than cold skin. Your pharmacist can demonstrate proper technique. Q3: How long does a Mounjaro injection take? A3: A Mounjaro injection typically takes 5–10 seconds to administer. The KwikPen is automatic — you press the button and hold it in place for 10 seconds to ensure the full dose is delivered. After injection, you can immediately remove the pen and apply light pressure if needed. Q4: What's the difference between NHS and private Mounjaro access in the UK? A4: NHS access requires GP referral to specialist weight management services, with potential waiting lists. Private access involves online consultation with a licensed UK prescriber and dispensing through GPhC-registered pharmacies, typically without waiting lists but at personal cost (£130–£320/month). Both require clinical assessment. Q5: Can I store Mounjaro at room temperature after opening? A5: Yes — unopened pens must be refrigerated at 2–8°C. Once you start using a pen, it can be kept at room temperature (below 30°C) for up to 30 days. Dispose of the pen after 30 days from first use, even if some medication remains. Never freeze Mounjaro.- 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.
What is BMI and how is it calculated?
BMI (Body Mass Index) is calculated by dividing your weight in kilograms by your height in metres squared. It's the standard screening tool used by the NHS to assess whether adults are a healthy weight.
Is BMI accurate for everyone?
BMI is a useful screening tool but doesn't account for muscle mass, bone density, or body fat distribution. Athletes may have a high BMI without excess fat. The NHS recommends using BMI alongside waist circumference for a more complete picture.
What are GLP-1 medications like Mounjaro and Wegovy?
GLP-1 receptor agonists are prescription medications that mimic gut hormones to reduce appetite and help with weight loss. Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two most widely used for weight management in the UK.
Am I eligible for GLP-1 weight loss medication in the UK?
Generally, you need a BMI of 30+ (obese) or 27+ with a weight-related health condition. You must be 18 or over. Use our BMI calculator to check.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with up to 22.5% weight loss. Wegovy (semaglutide) is GLP-1-only with up to 15-17% weight loss. Both are weekly injections.
Is this website free to use?
Yes, 100% free. No sign-up required. All tools work instantly in your browser and no personal data is stored on our servers.
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.