What Are the Weight Loss Injections?

Mounjaro and Wegovy are the two prescription weight loss injections most widely discussed. A third medicine — Saxenda (liraglutide) — is also prescribed for weight management in some countries, though Mounjaro and Wegovy are the newer options currently attracting most attention. Here is a factual overview of each.

Mounjaro (tirzepatide)

Mounjaro's active substance is tirzepatide, a dual GIP and GLP-1 receptor agonist. It acts on two appetite-regulating hormone pathways simultaneously. It is supplied as a pre-filled pen and is injected once a week. Dose strengths commonly associated with Mounjaro include 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg — though the dose a person is on at any given time is always determined by their prescriber, not self-selected.

Wegovy (semaglutide)

Wegovy's active substance is semaglutide, a GLP-1 receptor agonist. It acts on one appetite-regulating pathway. Like Mounjaro, it is a pre-filled pen injected once weekly. Commonly referenced dose strengths include 0.25 mg, 0.5 mg, 1 mg, 1.7 mg, and 2.4 mg.

What they have in common

• Both are prescription-only medicines — they cannot be obtained without a prescription from a qualified prescriber
• Both are self-injected once a week, typically into the abdomen, thigh, or upper arm
• Both work on appetite-related hormone pathways, commonly reducing feelings of hunger and increasing the sense of fullness
• Both are started at a low dose and adjusted over time under prescriber supervision
• Neither is insulin, and neither is a cosmetic quick fix — they are prescribed medicines used alongside diet and activity changes

Both Mounjaro and Wegovy carry a black triangle (▼) symbol in the UK, meaning they are subject to additional safety monitoring. Any side effects should be reported to a healthcare professional and, where applicable, to your national reporting scheme (such as the UK's Yellow Card scheme).

If you are researching the cost side of these medicines, the page on how much the weight loss injection costs covers that topic in more detail. You can also explore which injection may be considered for weight loss for a factual comparison — though the right choice for any individual is always a decision for their prescriber.

Once you are prescribed one of these medicines, keeping track of your injection sites and weekly schedule quickly becomes one of the most practical challenges of the journey. GLP Trackr is built specifically for this.

The app's injection-site tracking and rotation feature lets you log each injection — recording the site (abdomen, thigh, or upper arm), the date, and the dose strength. Based on your history, the app suggests where your next injection should go, making rotation automatic rather than something you have to remember manually. Rotating sites matters because injecting repeatedly into the same spot can affect how the medicine is absorbed.

Alongside site tracking, dose reminders mean you are less likely to let a weekly injection slip your mind — and if you do miss a dose, the app gives you a place to log it so you can discuss what to do next with your prescriber. Any decision about a missed or delayed dose belongs with your healthcare professional, not with an app.

For a broader look at everything involved in these medicines, the complete guide to weight loss injections is a good place to start.

If you experience any side effects that feel severe, persistent, or worrying, contact your healthcare professional promptly. GLP Trackr helps you record what you notice so you can have an informed conversation — it is not a substitute for clinical guidance.

Start logging your injections, tracking your rotation, and staying on schedule. GLP Trackr is free to try for seven days — available now on the App Store and Google Play.