Slimming Injections: What They Are and How to Stay on Track

Among the most widely discussed injectable medicines used for weight management are Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are prescription-only, once-weekly injections supplied as pre-filled pens. Semaglutide acts on GLP-1 receptors involved in appetite regulation, while tirzepatide acts on both GLP-1 and GIP receptors — making it a dual-action medicine. Many people describe effects such as a reduced sense of hunger, lower "food noise", and a feeling of fullness after smaller meals, though individual responses vary.

These medicines are not suitable for everyone, and suitability is always determined by a prescriber based on your individual health history. They are not the same as insulin, and they are not a cosmetic treatment — they are clinically prescribed medicines that sit alongside diet, activity, and ongoing medical supervision.

Common injection sites

Both Mounjaro and Wegovy are typically injected into subcutaneous (under-the-skin) tissue. The most commonly used sites are the abdomen, the front of the thigh, and the upper arm. Rotating between sites is generally recommended to allow each area time to recover and to help maintain consistent absorption. Your prescriber or the patient information leaflet that comes with your pen will give you the guidance specific to your medicine.

Other slimming injection names you may come across

You may encounter various names when researching this topic — including references to "slimming injection pens", "slimming pen injections", or medicines like Ozempic (a semaglutide medicine licensed for type 2 diabetes, sometimes called a diabetes slimming injection). The landscape of available medicines is evolving; your prescriber is the right person to discuss which, if any, is appropriate for you. For a broader overview, see our guide to weight-loss injections or explore what the evidence says about choosing a slimming injection.

If you have been prescribed one of these medicines and want to understand more about what is available, our page on slimming injections covers the landscape in more detail. Questions about access through different healthcare systems are covered in our guide to slimming injections on the NHS.

One of the most useful habits you can build when using a weekly injectable medicine is keeping a reliable log of every dose — which site you used, when you injected, and how you felt afterwards. GLP Trackr's injection-site tracking and rotation feature records each site you use and suggests your next one automatically, so you never have to remember which side you used last week.

Alongside site rotation, the app lets you log the date, time, and dose strength of every injection, giving you a clear, searchable history to refer back to — and to share with your prescriber at appointments. If you ever experience side effects such as nausea, fatigue, or injection-site reactions, the side-effect tracking feature lets you log symptoms and spot patterns over time, which can make your clinical conversations much more productive.

Because progress on a weekly injectable medicine is rarely just about the number on the scale, the app also captures weight, mood, energy, sleep, and food-noise levels in a quick daily check-in — so you build a picture of your whole journey, not just one data point.

GLP Trackr is a tracking and journaling companion — it is not a substitute for the guidance of your prescriber or doctor. If you experience any severe, persistent, or worrying symptoms, contact your healthcare professional promptly. Any questions about your dose, injection technique, or whether this medicine is right for you should be discussed with your prescriber.

Ready to take the guesswork out of injection-site rotation? GLP Trackr is available on the App Store and Google Play — start your free 7-day trial and let the app handle the tracking while you focus on the journey.