How Do Slimming Injections Work?

These medicines belong to a class that targets GLP-1 receptors — pathways involved in regulating blood sugar, appetite, and how quickly the stomach empties. Wegovy (semaglutide) is a GLP-1 receptor agonist, while Mounjaro (tirzepatide) acts on both GLP-1 and GIP receptors, making it a dual agonist. In practical terms, many people experience a noticeable reduction in what is sometimes called "food noise" — the persistent background preoccupation with eating — alongside a greater sense of fullness after meals.

Slower gastric emptying is a commonly reported effect, which can mean food sits in the stomach for longer. This effect often contributes to reduced appetite, though it is also linked to some of the gastrointestinal side effects — such as nausea or indigestion — that people commonly experience, particularly early on or after a dose adjustment. These effects are not universal, and your prescriber or doctor is best placed to explain what you might expect based on your own health history.

How the injection itself works

Both medicines are delivered via a pre-filled injection pen, administered once a week into the skin — typically at the abdomen, thigh, or upper arm. The injection site is rotated each week to avoid irritation and allow tissue to recover. Your prescriber or the patient information leaflet that came with your pen will give you specific guidance on technique; the key practical habit is keeping track of where you injected last time so you can move to a different site next week.

For a broader overview of these medicines and how they are used, see our guide to weight loss injections. You may also find it useful to read about slimming injections generally or explore how weight loss injections work in more detail.

One of the most practical challenges once you start a weekly injection is remembering exactly where you last injected — and the app's injection-site tracking is built specifically for this. Each time you administer your dose, you log the site (abdomen, thigh, or upper arm) and GLP Trackr keeps a rotation history so it can suggest where to inject next. Over time this takes the guesswork out of rotation entirely.

Alongside site tracking, the app logs each dose with its date, time, and strength, and gentle reminders mean a dose is far less likely to slip through the cracks in a busy week. If you want to monitor how you feel in the days following each injection — whether that is nausea, energy levels, or appetite changes — the side-effect and daily check-in features let you build a picture of your own patterns, which can be genuinely useful to share with your prescriber at your next appointment.

If you are curious about access to these medicines in your area, our page on slimming injections and prescribing pathways covers the topic in neutral, general terms.

Any concerns about how slimming injections are working for you — or any symptoms that feel severe, persistent, or out of the ordinary — should always be discussed with your healthcare professional promptly. GLP Trackr helps you record what you experience; it is not a substitute for clinical advice.

Ready to take the guesswork out of injection-site rotation? Download GLP Trackr on the App Store or Google Play and start a free 7-day trial — your injection log, rotation reminders, and dose history will all be in one place from day one.