Best Slimming Injections for Weight Loss: What to Know

Mounjaro and Wegovy are prescription-only medicines administered by subcutaneous injection, typically once a week. They are not interchangeable over-the-counter products — both require a prescription from a qualified healthcare professional, and suitability is assessed individually.

The medicines at a glance

• Mounjaro (tirzepatide) acts on two receptors — GLP-1 and GIP — to help regulate appetite and the sense of fullness. It is supplied as a pre-filled pen.
• Wegovy (semaglutide) acts on GLP-1 receptors to produce similar effects and is also supplied as a pre-filled pen.

Both medicines are typically started at a lower dose, with the prescriber adjusting the dose over time based on how the individual responds. These are not cosmetic quick fixes; they are prescription treatments used alongside dietary changes and physical activity under clinical supervision.

Injection sites and rotation

Both medicines are injected under the skin. Common sites include the abdomen, outer thigh, and upper arm. Rotating the injection site with each dose is generally recommended to avoid irritation or changes to the tissue at any one spot. Your prescriber or the patient information leaflet that came with your pen will give you guidance specific to your medicine.

For a broader look at how these medicines are used in practice, see our guide to weight-loss injections. You may also find it useful to read about injections for weight loss and how the injection process fits into the wider treatment journey.

Remembering which site you used last week — and whether your next dose is due tomorrow or the day after — is one of the small but real challenges of a weekly injection routine. GLP Trackr is built specifically for this.

The app's injection-site tracking and rotation feature lets you log each injection — the site you used, the dose strength, and the date — and then suggests where to inject next time based on your rotation history. Over a few weeks, you build a clear record you can glance at before every dose rather than trying to remember.

Alongside that, dose reminders mean your weekly schedule stays on track without relying on memory alone. If you ever miss a dose, the app helps you log it so you can discuss what happened with your prescriber — dose decisions always belong with them, not with an app.

Many people also use the side-effect tracker to note how they felt in the days after an injection, which can reveal patterns over time that are genuinely useful to bring to a prescriber appointment.

If you want to explore how different injection approaches compare, the pages on slimming injections and fat-reduction injections offer further context.

Always follow the guidance of your prescriber or doctor — they know your full medical history and are best placed to advise on your injection technique, site choices, and any concerns. If you experience a reaction at an injection site that is severe or does not resolve, contact your healthcare professional promptly. Any side effects worth reporting should be flagged to a healthcare professional and, where relevant, to your national reporting scheme (such as the UK's Yellow Card scheme).

Ready to take the hassle out of tracking your weekly injections? GLP Trackr is free to try for 7 days — download it on the App Store or Google Play and let the app handle the rotation reminders from your very first dose.