Are Weight Loss Injections Safe?

Because Mounjaro and Wegovy are prescription-only medicines, they are dispensed only when a prescriber has determined that the benefits are likely to outweigh the risks for that specific person. That assessment takes into account your medical history, any other medicines you take, and individual health factors.

Commonly reported side effects

The most frequently reported side effects are gastrointestinal — nausea, vomiting, diarrhoea, constipation, and indigestion. These are most common when starting the medicine or after a dose adjustment, and many people find they settle over time. Other commonly reported effects include fatigue, headache, dizziness, and reactions at the injection site such as mild redness or itching.

Less common but important considerations

Both medicines carry information in their official prescribing details about rarer but more significant concerns, including effects on the gallbladder, pancreas, and — particularly in people managing diabetes alongside other glucose-lowering medicines — blood sugar levels. Your prescriber will have discussed any risks relevant to your circumstances before starting you on treatment. If you experience severe or persistent abdominal pain, jaundice, or any symptom that worries you, contact your healthcare professional promptly rather than waiting for a scheduled appointment.

Additional monitoring

Both Mounjaro and Wegovy carry a black triangle (▼) designation, which means they are subject to additional monitoring so that new safety information can be identified quickly. You are encouraged to report any side effects you experience to your national reporting scheme (such as the UK's Yellow Card scheme, or the equivalent in your country) as well as to your own prescriber or doctor. According to information held on the electronic Medicines Compendium (eMC), full details of known side effects and contraindications are listed in the Summary of Product Characteristics for each medicine.

If you would like a broader overview of how these medicines work and what to expect, the guide to weight loss injections covers the key facts in one place. You may also find it useful to read about what a weight loss injection involves for general context.

One of the most practical things you can do while taking a weight loss injection is keep a clear record of how you feel — not to replace clinical oversight, but to support it. When you can show your prescriber a log of side effects, their timing, and how they relate to your dose schedule, those conversations become more useful for both of you.

GLP Trackr's side-effect tracker is built exactly for this. You can log symptoms as they happen — nausea, fatigue, injection-site reactions, digestive changes — and the app surfaces patterns over time, so you can see whether a symptom tends to appear on certain days after your injection or eases as weeks go on. That kind of record is far more informative to bring to a prescriber appointment than trying to recall the past few weeks from memory.

Alongside side-effect logging, the app tracks your injection sites and suggests your next rotation — useful for reducing localised skin reactions at the injection site, which are among the more commonly reported issues. And dose reminders mean you're less likely to accidentally miss a scheduled injection and then be uncertain about what to do next.

GLP Trackr is a tracking and journaling tool — it is not a medical service, and nothing it records or shows constitutes medical advice. Always follow the guidance of your prescriber or doctor, who knows your full health history. If any symptom feels severe, persistent, or out of the ordinary, contact your healthcare professional rather than relying on app data alone.

For questions about the cost or access aspects of your treatment, you might also find these pages useful: understanding the cost of weight loss injections and how weight loss injections are obtained.

Want to keep a proper record of your side effects and injection history in one place? GLP Trackr is free to try for 7 days — available on the App Store and Google Play, built specifically for people on Mounjaro and Wegovy.