Weight Loss Injections: How Much You Need, How They Work, and What to Expect

Mounjaro and Wegovy both act on appetite-regulating pathways in the body. Wegovy (semaglutide) is a GLP-1 receptor agonist, while Mounjaro (tirzepatide) acts on both GLP-1 and GIP receptors. In practical terms, many people experience a reduced appetite and an increased sense of fullness after eating — often described as quieter "food noise" — as well as slower stomach emptying, an effect that commonly eases over time.

How long do they take to work?

Noticeable changes in appetite can begin within the first few weeks for some people, though meaningful weight changes typically become more apparent over several months. Results vary considerably between individuals and depend on factors including diet, activity, and how your body responds to the medicine. There is no universal timeline — your prescriber is best placed to talk you through what to expect for your specific situation.

How many injections do you need?

Because both medicines are taken once a week, the number of injections adds up steadily: roughly four per month, around 52 per year. Treatment duration is determined by your prescriber based on your health goals and how you are responding — it is not a fixed short course. Staying consistent with your weekly schedule matters, which is why tracking each dose is so useful.

Where are the injections given?

Both medicines are injected subcutaneously (just under the skin) into common sites including the abdomen, outer thigh, or upper arm. Rotating between sites each week is generally recommended to reduce the chance of skin reactions at any one spot. Your prescriber or the patient information leaflet that came with your pen will guide you on technique.

For more background on these medicines and what they involve, see our guide to weight loss injections. If you are thinking about the financial side of treatment, our pages on what weight loss injections cost and weight loss injection pricing cover that topic in more detail.

One of the most practical things you can do on a weekly injection schedule is keep a clear record of every dose — and that starts with knowing which injection site you used last time. GLP Trackr's injection-site tracking feature logs each site (abdomen, thigh, or arm) and automatically suggests where to inject next, so rotation becomes effortless rather than something you have to remember yourself.

Alongside site tracking, the app logs the date, time, and dose strength of every injection in one place. Over weeks and months, this builds a complete picture of your treatment history — useful for spotting patterns and for sharing an accurate summary with your prescriber at appointments. Dose reminders help make sure a weekly shot is never accidentally missed.

If you are curious about options like finding good-value injection options, that is a separate decision that sits with your prescriber and a registered pharmacy — GLP Trackr is a tracking companion for people already prescribed these medicines, not a source of supply or purchasing advice.

If you ever experience symptoms that concern you — whether at the injection site or more generally — always contact your healthcare professional promptly. GLP Trackr helps you record what you notice so you can describe it accurately when you do speak to them, but it is not a substitute for their clinical advice.

Ready to take the guesswork out of injection rotation? GLP Trackr logs every site and nudges you toward the right one next week. Start your free 7-day trial — available on the App Store and Google Play.