Weight Loss Injection Risks: What People on Mounjaro and Wegovy Should Know

The risks associated with injectable GLP-1 and dual GIP/GLP-1 medicines fall into two broad categories: commonly reported, usually mild effects, and rarer but more serious concerns that your prescriber will have discussed with you before starting treatment.

Commonly Reported Side Effects

Gastrointestinal symptoms are the most frequently reported effects. These include nausea, vomiting, diarrhoea, constipation, indigestion, and reflux. Many people also report burping, fatigue, headache, dizziness, and reactions at the injection site itself — such as redness, bruising, or mild swelling.

These effects are particularly common shortly after a dose or following a dose adjustment, and many people find they ease over time as the body adjusts. They are not universal, and their severity varies considerably from person to person.

More Serious Risks to Be Aware Of

A small number of people may experience more significant effects. According to information from the electronic Medicines Compendium (eMC), which hosts the official prescribing information for these medicines, serious but less common risks can include pancreatitis, gallbladder problems, and allergic reactions. Changes in mood or mental health have also been reported and should be discussed with a healthcare professional promptly.

If you experience severe or persistent abdominal pain, significant vomiting that prevents you eating or drinking, yellowing of the skin or eyes, difficulty breathing, or any symptom that feels serious or unusual, contact your healthcare professional without delay.

Injection-Site Risks

Repeatedly injecting into the same spot can cause localised skin changes such as lumpiness or hardening beneath the skin (lipohypertrophy). Rotating your injection site — between the abdomen, outer thigh, and upper arm — reduces this risk. Your prescriber or the patient information leaflet that came with your pen can advise on correct technique.

For a broader overview of how these medicines work and what to expect, see our guide on weight loss injections and how to use them. You may also find it useful to read about what a weight loss injection involves and how people commonly experience their treatment.

One of the most practical things you can do when managing the risks of a weekly injection is to keep a clear, consistent record — both of where you inject and of how you feel after each dose. That record becomes genuinely useful when you speak to your prescriber.

GLP Trackr's injection-site tracking feature is built precisely for this. Each time you inject, you log the site — abdomen, thigh, or upper arm — and the app keeps a rotation history so it can suggest your next site automatically. This takes the guesswork out of rotation and helps reduce the skin-change risk that comes from reusing the same spot.

Alongside site tracking, the app's side-effect log lets you record how you feel after each injection: nausea, fatigue, dizziness, injection-site reactions, or anything else worth noting. Over time you can see whether certain patterns emerge — for example, whether symptoms cluster in the days after a dose. That kind of structured record is far more useful to bring to a prescriber appointment than a vague recollection.

GLP Trackr also sends dose reminders so your weekly schedule stays on track, and every dose is timestamped and logged, giving you a clear history to reference if questions arise.

If you are weighing up what is involved before starting, our page on choosing a weight loss injection covers what to discuss with your prescriber, and our guide on accessing these medicines explains the prescription pathway.

Important: GLP Trackr is a tracking and journaling app — it is not a substitute for clinical guidance. Any symptom that is severe, persistent, or worrying should be discussed with your healthcare professional promptly. Decisions about your dose, your treatment, or how to manage a side effect are always for your prescriber, not an app. Most countries also have national reporting schemes for side effects of prescription medicines — ask your prescriber or pharmacist about the appropriate scheme in your country (such as the UK's Yellow Card scheme).

Log your injection sites, track how you feel, and build a record that actually helps your appointments. GLP Trackr is free to try for 7 days — available now on the App Store and Google Play.