What Is the Strongest Weight Loss Injection?

Both tirzepatide and semaglutide are prescription-only, once-weekly injectable medicines used for weight management in people who meet specific clinical criteria determined by their prescriber.

How they work

Semaglutide (Wegovy) is a GLP-1 receptor agonist. It mimics a hormone involved in regulating appetite and slowing gastric emptying, which many people experience as reduced hunger and a quieter relationship with food. Tirzepatide (Mounjaro) acts on both GLP-1 and GIP receptors — a dual mechanism that is relatively newer in this class of medicine. According to information available through the electronic Medicines Compendium, both medicines are supplied as pre-filled injection pens and are started at a low dose, with any adjustment made by the prescriber over time.

Common injection sites

Both medicines are injected subcutaneously — under the skin — typically into the abdomen, upper thigh, or upper arm. Rotating between sites is generally recommended to reduce the chance of localised reactions or discomfort at any one area. Your prescriber or doctor, along with the patient information leaflet that came with your pen, is the best guide to the specific injection technique for your medicine.

Important considerations

Neither medicine is suitable for everyone — suitability is assessed individually by a prescriber. Both carry a black triangle (▼) designation, meaning side effects should be reported to your national reporting scheme (such as the UK's Yellow Card scheme) as well as to a healthcare professional. Commonly reported side effects include nausea, constipation, and other gastrointestinal symptoms, particularly in the early weeks.

For a broader overview of how these medicines are used, the guide to weight loss injections covers both in more detail. If you have questions about the practicalities of a single injection, the page on how a weight loss injection works is a useful companion read.

Once you are prescribed either tirzepatide or semaglutide, staying consistent with your weekly injection schedule — and rotating your injection sites correctly — becomes a routine part of life. GLP Trackr is built specifically to make that routine easier to manage.

Site rotation, made effortless

The app's injection-site tracking feature lets you log each site you use — abdomen, thigh, or arm — and automatically suggests where to inject next, so you never have to mentally keep track of your rotation history. Over time you can see a clear record of every site used, which can be useful to raise with your prescriber if you notice any localised reactions.

Dose logging and reminders

Every dose you take can be logged with the date, time, and strength, creating a complete record of your treatment history. The app's dose reminder feature means a weekly injection is far less likely to be forgotten — particularly useful during weeks when your routine changes.

If you have questions about the cost of your prescription or where to obtain your medicine, those decisions belong with your prescriber or a registered pharmacy in your country — GLP Trackr does not sell, supply, or source medication. You can find neutral background on what affects the cost of weight loss injections, or read about how people access weight loss injections through a prescriber and pharmacy.

Always follow the guidance of your prescriber or doctor — they know your full medical history and are the right person to advise on your dose, injection technique, and any side effects you experience. GLP Trackr helps you record your journey so those conversations are better informed; it is not a substitute for clinical care.

Ready to take the guesswork out of site rotation and dose tracking? GLP Trackr is free to try for 7 days — available now on the App Store and Google Play.