Prescription Weight Loss Injections: A Guide for People Already on Treatment

Both Mounjaro and Wegovy are administered as subcutaneous injections — meaning they are injected just beneath the skin, not into a muscle or vein. The three sites most commonly used are the abdomen, the front of the thigh, and the upper arm. Each comes supplied as a pre-filled pen, designed so that the injection process is straightforward once you have been shown how to use it by your prescriber or a healthcare professional.

Why injection site rotation matters

Rotating between injection sites is an important part of using these medicines correctly. Injecting repeatedly into exactly the same spot can lead to skin changes at the site, which may affect how the medicine is absorbed. Most prescribers recommend moving systematically between areas — for example, alternating sides of the abdomen, or cycling through abdomen, thigh, and arm across successive weeks.

Your prescriber or the patient information leaflet that came with your pen will explain the rotation approach recommended for your specific medicine. If you are unsure about technique or site choice, always check with your prescriber or doctor rather than guessing.

Prescription-only medicines: what that means in practice

Mounjaro and Wegovy are prescription-only medicines. This means they can only be legally obtained through a prescriber and a registered pharmacy — there is no non-prescription version of either medicine available. Anyone you see marketing a "non prescription weight loss injection" with the same active ingredients (tirzepatide or semaglutide) would warrant careful scrutiny; always verify any product with your prescriber before use.

For a broader overview of how these medicines fit into the wider landscape, see our guide to weight loss injections. If you are thinking about what treatment costs look like as part of managing your journey, our page on weight loss injection costs and what affects them covers this topic in factual, neutral terms.

Staying on top of rotation is one of those small habits that is easy to let slip — especially once weekly injections feel routine. GLP Trackr is built specifically for people already on Mounjaro or Wegovy, and injection-site tracking is one of the features at the heart of the app.

Each time you inject, you can log the site you used — abdomen, thigh, or upper arm, and which side. The app keeps your full rotation history and suggests your next site automatically, so you never have to try to remember where you injected three weeks ago. Alongside site logging, the app records your dose and the date and time of each injection, giving you a clear, searchable history of your treatment.

Dose reminders are built in too — a gentle nudge on your chosen day each week, so your weekly schedule stays on track without having to rely on memory alone.

If you want to read more about getting organised with your treatment routine, our page on staying consistent with your prescription weight loss injections goes into more practical detail.

GLP Trackr is free to try for seven days and is available on the App Store and Google Play. If you are already on your treatment and want your injection history in one reliable place, download it and see how it fits into your routine — no obligations during the trial.

A note on safety: if you experience any injection-site reactions that are severe, spreading, or do not settle, contact your healthcare professional promptly. Any questions about your dose, your injection schedule, or whether a symptom is related to your medicine should always go to your prescriber or doctor — they know your full history and are best placed to advise. GLP Trackr helps you record what is happening so those conversations are better informed; it is not a substitute for clinical guidance.