The 'Skinny Jab': What You Need to Know About Mounjaro

Mounjaro is the brand name for tirzepatide, a prescription-only, once-weekly injectable medicine. It acts on two appetite-regulating receptors — GLP-1 and GIP — which is why it is sometimes described as a dual-action medicine. It is supplied as a pre-filled pen and is injected once a week, typically into the abdomen, outer thigh, or upper arm.

The terms "skinny jab", "slimming jab", and "diet jab" are colloquial labels that have grown in popular use, but they do not capture the clinical picture. Mounjaro is a prescription medicine — suitability, dosing, and any adjustments are decided by your prescriber or doctor, not by the name it goes by online.

Injection Sites and Rotation

Most people are advised to rotate injection sites so that no single area is used repeatedly. Common sites are the abdomen (at least a few centimetres from the navel), the front of the thigh, and the upper arm. Rotating between and within these areas helps reduce the chance of skin reactions or changes at the injection site. For guidance specific to your pen and how to use it, always refer to the patient information leaflet that came with your medicine or ask your prescriber.

If you are looking for more on where to inject, the page on choosing your Mounjaro injection site goes into further detail. You may also find it useful to read about what the fat jab means in practice and how it fits into a broader weight-loss journey. For a wider look at injectable weight-loss medicines, see our guide to the Mounjaro weight-loss jab.

Keeping track of a weekly injection schedule — including which site you used last and when your next dose is due — is easy to let slip. GLP Trackr's injection-site tracking and rotation feature logs each site you use and suggests where to inject next, so rotation becomes automatic rather than something you have to remember manually.

Alongside site logging, the app records the date, time, and dose strength of every injection, giving you a clear history of your treatment in one place. Dose reminders mean you are less likely to lose track of your weekly schedule, particularly during the early weeks when the routine is still new.

All of this logged data can be genuinely useful at your next prescriber appointment — you arrive with an accurate record rather than trying to recall details from memory. GLP Trackr's doctor report feature lets you bring a clear summary of your journey to those conversations.

For a broader look at everything that goes into tracking your injections and progress, the weight-loss injections hub covers the full picture.

A note on safety: always follow the injection guidance provided by your prescriber or doctor and the leaflet that came with your pen. If you notice anything unusual at an injection site — or have any concerns about your medicine — contact your healthcare professional promptly. Any side effects worth noting can also be reported to your national reporting scheme (such as the UK's Yellow Card scheme).

Ready to take the guesswork out of injection-site rotation? GLP Trackr is free to try for seven days — available now on the App Store and Google Play.