The Weight Loss Injection: What It Is, What to Expect, and How to Track It

The two most widely prescribed weight loss injections are Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are once-weekly injectable medicines supplied as pre-filled pens that you administer yourself, typically into the abdomen, thigh, or upper arm. You can read a broader overview of how weight loss injections work for more background on the full category.

What do they do?

Semaglutide acts on GLP-1 receptors involved in appetite regulation. Tirzepatide acts on both GLP-1 and GIP receptors. Many people report a reduced sense of hunger, a greater feeling of fullness after smaller amounts of food, and a quietening of what is often described as "food noise" — the persistent preoccupation with eating. For a closer look at what is actually inside these injections, including the active ingredients, that page goes into more detail.

Does the injection hurt?

Most people find the injections largely painless — the needles are very fine and short. Some mild discomfort, redness, or itching at the injection site is commonly reported, particularly in the early weeks. Rotating your injection site with each dose is widely recommended to reduce local reactions and allow the skin to recover.

How safe are they, and what are the side effects?

These are prescription-only medicines because their suitability is assessed individually by a prescriber. Commonly reported side effects include nausea, vomiting, diarrhoea, constipation, indigestion, and fatigue — particularly in the first few weeks or after a dose adjustment. These often ease over time for many people. If you experience anything severe, persistent, or worrying, contact your healthcare professional promptly. Any concerns about suitability or safety should always be discussed with your prescriber or doctor, who knows your full medical history. Side effects can also be reported to your national reporting scheme (such as the UK's Yellow Card scheme).

Can anyone have the weight loss injection?

No — suitability is determined by a prescriber based on individual health factors. These medicines are not appropriate for everyone, and the decision rests entirely with your healthcare professional. If you are wondering whether you might be entitled to access through a particular healthcare system, that is a question for your prescriber or doctor, as eligibility criteria vary by country and by how care is organised locally.

Can you buy the weight loss injection yourself?

Mounjaro and Wegovy are prescription-only medicines and cannot be legally purchased without a valid prescription. GLP Trackr does not sell, supply, or source these medicines in any way. For information on how to obtain them, speak to your prescriber or a registered pharmacy in your country. If you are already prescribed and want to understand more about the process, the page on accessing weight loss injections covers this in a factual, neutral way.

Once you are prescribed a weight loss injection, the practical challenge becomes staying consistent — remembering your weekly dose, rotating sites correctly, and noticing how your body responds over time. That is exactly where GLP Trackr is designed to help.

Injection-site tracking and rotation

The app logs each injection site — abdomen, thigh, or upper arm — and tracks your rotation history so you always know where you injected last. Rather than trying to remember, you can simply check the app and let it suggest your next site. Consistent rotation is an easy habit to build when the record-keeping is done for you.

Dose logging and reminders

Every dose you take — including the date, time, and strength — is stored in one place. Gentle reminders mean a weekly injection is far less likely to slip past unnoticed. If you do miss a dose, you can log that too and bring the record to your next prescriber appointment; any decision about what to do belongs with your healthcare professional, not with an app.

Side-effect tracking

Because side effects like nausea or injection-site reactions are common, especially early on, being able to log how you feel day by day helps you spot patterns. That log becomes genuinely useful when you have a conversation with your prescriber about how your body is adjusting.

GLP Trackr is a companion for people already on their prescribed weight loss injection journey — it is not a medical service and does not replace your prescriber's guidance. Always follow the advice of the healthcare professional managing your treatment.

Start building your injection log today — GLP Trackr is free to try for 7 days on the App Store and Google Play. Download it free and see how straightforward staying consistent can be.