Are the Slimming Injections Safe?

Both Mounjaro and Wegovy are prescription-only medicines. Prescription-only status exists precisely because these medicines require clinical oversight: a qualified prescriber evaluates whether the medicine is appropriate, monitors progress, and adjusts the plan over time. That clinical relationship is a core part of the safety framework around these injections.

Commonly reported side effects

The most frequently reported side effects are gastrointestinal — nausea, vomiting, diarrhoea, constipation, and indigestion are all commonly noted, particularly in the earlier weeks of treatment or after a dose adjustment. Injection-site reactions, fatigue, headache, and dizziness are also reported by some people. These effects are not universal, and for many people they ease as the body adjusts.

Side effects that need prompt attention

Some symptoms warrant contacting a healthcare professional promptly rather than waiting to see if they pass. These include severe or persistent abdominal pain, signs of an allergic reaction, significant mood changes, or anything that feels serious or unusual. Your prescriber or doctor is the right person to advise you — they know your individual history in a way that general information cannot replicate.

Who these medicines are not for

These medicines are not suitable for everyone. Suitability depends on medical history, other medicines being taken, and individual circumstances. That assessment happens at the prescribing stage, which is why obtaining these injections without a prescription and proper clinical oversight carries real risk. You can read more about the broader context of these medicines on our weight-loss injections overview, or explore what slimming injections involve in more detail.

According to NHS guidance, both medicines carry a black triangle (▼) designation, meaning they are subject to additional monitoring. Any suspected side effects should be reported to your healthcare professional and to your national reporting scheme — for example, the UK's Yellow Card scheme, or whichever equivalent scheme operates in your country.

One of the most practical things you can do while taking a prescription weight-loss injection is keep a consistent record of how you feel — not just your weight, but your energy, any side effects, injection sites, and patterns over time. That record becomes genuinely useful when you speak with your prescriber or doctor.

GLP Trackr's side-effect tracking feature is built exactly for this: log symptoms as they happen, note their severity, and the app builds a timeline you can actually show your prescriber at your next appointment. Spotting that nausea reliably peaks on day two after an injection, or that fatigue clusters around a particular week, is the kind of pattern that is easy to miss without a log — and useful to have when discussing how treatment is going.

The injection-site tracker also helps you rotate sites properly, which matters for comfort and for avoiding localised reactions at a single site. Log each injection and let the app suggest where to inject next time.

If you have questions about the costs involved in your treatment, our page on how much slimming injections cost covers what factors are typically involved. For a closer look at the safety question specifically, see our related page on slimming injections and safety.

Important: GLP Trackr is a tracking and journaling app — it is not a substitute for clinical advice. If you experience symptoms that are severe, persistent, or concern you, contact your healthcare professional promptly. Any questions about whether your medication is right for you, or how to adjust it, belong with your prescriber — not an app.

Want a clear, organised record of your injection journey to bring to your next appointment? Download GLP Trackr on the App Store or Google Play and start a free 7-day trial — no commitment needed.