Slimming Injections: What They Are and How to Track Your Journey

Both Mounjaro and Wegovy are administered as subcutaneous injections — meaning they are delivered just beneath the skin, not into muscle. The three sites most commonly recommended in product information are the abdomen, the front of the thigh, and the upper arm. Each pre-filled pen is designed for once-weekly use, and the injection day is typically kept consistent from week to week.

Why injection-site rotation matters

Rotating the site with each injection — rather than returning to the same spot every week — helps reduce the chance of localised skin reactions such as redness, swelling, or hardened tissue at the injection area. These are among the commonly reported reactions associated with repeated use of a single site. Staying within the same general area (for example, the abdomen) but moving to a different spot each time is a practical approach many people use.

It is worth noting that terms like calf slimming injections or shoulder slimming injections sometimes appear in searches, but the standard guidance for GLP-1 weight-loss injections does not include the calf as a recommended site. Always follow the specific instructions provided with your medicine and confirmed by your prescriber — your patient information leaflet is the definitive reference for your pen.

Pen handling and storage

Pre-filled pens for medicines like Mounjaro and Wegovy have specific storage requirements. As a general principle, unused pens are typically stored in a refrigerator, and once in use they can usually be kept at room temperature for a defined period — but always check the leaflet that came with your pen or the electronic Medicines Compendium entry for the exact figures, rather than relying on memory. Never use a pen past its expiry date or if it has been stored incorrectly.

For more on the broader landscape of weight loss injections, including how these medicines fit into a managed programme, our main guide covers the topic in depth. You may also find it useful to read about potential risks and side effects of slimming injections so you can recognise what to watch for and discuss with your prescriber. If you are curious about how slimming injections are accessed through public health services, or whether you can get slimming injections through a national health service, those pages explain the general picture in more detail.

Remembering which site you used last week — and whether it was the left or right side — is surprisingly easy to lose track of across a months-long weekly schedule. GLP Trackr's injection-site tracking feature is built specifically for this: log each injection with the site and side, and the app keeps a rotation history so it can suggest where to inject next. There is no need to rely on memory or notes.

Alongside site rotation, the app logs each dose — the strength, date, and time — so your full injection history is in one place. Paired with dose reminders, it means a weekly injection is far less likely to be missed or accidentally doubled up.

If you experience any injection-site reactions or other symptoms, the side-effect tracker lets you note them as they happen and spot patterns over time. That kind of record is genuinely useful to bring to a conversation with your prescriber — it turns vague recollections into a clear timeline.

You can also explore how Saxenda compares as a slimming injection option, or read more about what to expect in the early weeks of slimming injections and how to manage your injection routine as your dose progresses.

Always follow the injection guidance provided by your prescriber or doctor — they know your individual circumstances and the specific product you have been prescribed. If you notice any injection-site reaction that is severe, spreading, or not resolving, contact your healthcare professional promptly.

Ready to take the guesswork out of your injection routine? GLP Trackr is free to try for 7 days — download it on the App Store or Google Play and let it handle your rotation history from your very first log.