What the 'Skinny Jab' Actually Is and Where It Goes
Mounjaro is a prescription-only, once-weekly injectable medicine containing tirzepatide, a dual GIP and GLP-1 receptor agonist. It is supplied as a pre-filled pen and is administered as a subcutaneous injection — meaning it goes into the fatty tissue just beneath the skin, not into a muscle or vein.
Common injection sites
Three areas are generally used for subcutaneous injection with a pre-filled pen like Mounjaro:
- Abdomen — the area around the stomach, avoiding the few centimetres immediately around the navel
- Outer thigh — the front or outer aspect of the upper leg
- Upper arm — the outer, fatty area of the upper arm (often easier with assistance)
For the specific technique your prescriber recommends, always refer to the patient information leaflet that came with your pen or ask your healthcare professional directly. The guidance here is general and does not replace clinical instruction.
Why rotating sites matters
Using the same spot repeatedly can cause localised reactions — small lumps or areas of hardened skin (lipohypertrophy) that may affect how the medicine is absorbed. Rotating between sites, and moving slightly within each site each week, helps keep the skin tissue healthy and absorption consistent.
If you want to read more about weight-loss jabs in general or the specifics of Mounjaro as a weight-loss injection, those pages cover the broader context. You may also find it useful to explore fat jabs and Mounjaro for more on how the medicine is commonly described.
average weekly weight change in the first 16 weeks of Mounjaro & Wegovy use*
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Tracking Your Injections with GLP Trackr
Keeping a reliable record of each dose is one of the most practical things you can do on a weekly injection schedule — and it is exactly what GLP Trackr is built for.
Injection-site rotation made automatic
GLP Trackr lets you log every injection: the date, the dose strength, and the site you used (abdomen, thigh, or arm). The app tracks your rotation history and suggests your next site, so you never have to remember which side you used last week. Over time, your injection log becomes a clear, searchable record you can share with your prescriber if anything needs reviewing.
Dose reminders
Because Mounjaro is taken once weekly, it is surprisingly easy to lose track of the day — especially in the early weeks when the routine is still forming. GLP Trackr's dose reminders send a gentle prompt so your weekly schedule stays on track without having to rely on memory alone.
For a wider view of weekly injection management, visit the weight-loss injections hub, which covers the full range of topics around injectable weight-management medicines.
If you notice any injection-site reactions — such as redness, swelling, or persistent discomfort — log them in the app and bring them up with your prescriber or doctor at your next appointment. Any side effect that is severe, spreading, or concerns you should be discussed with a healthcare professional promptly rather than waited out.
Ready to take the guesswork out of your weekly injection routine? GLP Trackr's site-rotation tracker and dose reminders are free to try — download on the App Store or Google Play and start a 7-day free trial today.
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Start every day with a 60-second wellness check-in. Log how you're feeling, track nausea, appetite, energy, and mood — giving you and your care team a complete picture of how your medication is working.
Injection Tracking
Log every dose with a single tap. Track your dose history, phase in your cycle, estimated medication levels, and upcoming injection dates — with reminders so you never miss a scheduled shot.
Hydration Reminders
Staying hydrated is especially important on GLP-1 medications. Set daily water targets, log intake throughout the day, and receive smart nudges when you're falling behind your goal.
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Browse 50+ high-protein, GLP-1-friendly recipes filtered by meal type, prep time, and dietary needs. Every recipe includes full nutrition info, step-by-step instructions, and tips for eating with side effects.
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Beautiful, easy-to-read charts show your weight loss trajectory, weekly nutrition trends, medication responses, and wellbeing scores over time — turning raw data into genuine insights.
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Snap a photo of any meal and get a full nutrition breakdown in seconds — calories, protein, carbs, fat, and fibre. No searching. No manual logging. Just point, snap, and track.
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Log walks, workouts, and movement with activity targets that flex with your energy levels. On lower-energy dose days, gentler targets keep you moving without burning out.
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Frequently asked questions.
'Skinny jab' is a colloquial term for weekly injectable weight-management medicines. Mounjaro (tirzepatide) is a prescription-only once-weekly injection that falls under this informal description. It is only available when prescribed by a qualified healthcare professional.
Mounjaro is injected subcutaneously — into the fatty tissue beneath the skin — at one of three common sites: the abdomen, outer thigh, or upper arm. Your prescriber or the patient information leaflet that came with your pen will confirm the technique recommended for you.
Yes, rotating injection sites is generally recommended. Using the same spot repeatedly can cause skin changes that may affect absorption. Moving between the abdomen, thigh, and arm — and shifting slightly within each area — helps keep tissue healthy. Your prescriber can advise on a rotation pattern that suits you.
GLP Trackr lets you log each injection's date, dose strength, and site. The app tracks your rotation history and suggests your next site automatically, and dose reminders help you stay on your weekly schedule.
Mild redness or sensitivity at the injection site is commonly reported and often settles quickly. If a reaction is severe, spreading, persistent, or worrying you, contact your healthcare professional promptly — do not wait for your next scheduled appointment.