Are Slimming Injections Safe?

Both Mounjaro and Wegovy are prescription-only medicines, meaning they can only be supplied under the supervision of a qualified prescriber. That prescription-only status exists precisely because individual suitability, medical history, and ongoing monitoring all matter for safe use.

Commonly reported side effects

The most frequently reported side effects are gastrointestinal — nausea, vomiting, diarrhoea, constipation, and indigestion are all commonly noted, particularly when a dose is first started or adjusted. Fatigue, headache, dizziness, and injection-site reactions are also reported by some people. According to NHS guidance, these effects are often most noticeable early in treatment and tend to ease over time for many people.

When to seek medical attention

Some symptoms warrant prompt attention from a healthcare professional. These include severe or persistent abdominal pain, signs of an allergic reaction, significant mood changes, or any symptom that feels unusual or worrying. If you experience anything severe or persistent, contact your healthcare professional without delay — do not wait until your next scheduled appointment.

Who these medicines are not suitable for

Suitability is always determined by a prescriber. These medicines are not appropriate for everyone; certain personal or family medical histories, other medications, and conditions such as a history of pancreatitis or thyroid problems may affect whether they can be used safely. Your prescriber will have considered this before issuing your prescription.

Both medicines carry a black triangle (▼) designation in the UK, meaning that reporting any suspected side effects to your national reporting scheme — such as the UK Yellow Card scheme, or the equivalent scheme in your country — is particularly encouraged. You can find more context on NHS guidance on these medicines.

For a broader overview of how these treatments work and what to expect, see our guide to weight loss injections. You may also find it helpful to read about slimming injections generally and whether the slimming injections are considered safe in more detail.

One of the most practical things you can do while using a prescription slimming injection is keep a clear, consistent record of how your body is responding — and that record becomes genuinely useful when you speak to your prescriber.

Log side effects and spot patterns over time

GLP Trackr's side-effect tracker lets you log symptoms as they happen — nausea, fatigue, injection-site reactions, or anything else you notice — and view them over time. Patterns that might not be obvious day to day become clear across weeks, giving you something concrete to discuss at your next appointment rather than trying to recall how you felt three weeks ago.

Track injection sites and rotation

For people using once-weekly injectable pens, rotating injection sites (abdomen, thigh, upper arm) is generally recommended to reduce localised reactions. GLP Trackr logs each site you use and suggests your next rotation automatically, so you do not have to remember manually. If you are also wondering about how slimming injections are accessed through healthcare services, your prescriber is the right person to ask about your individual situation.

Your prescriber or doctor is always the right person to turn to with safety questions — GLP Trackr helps you record what is happening so those conversations are better informed, not replace them. If anything feels severe, persistent, or worrying, contact a healthcare professional promptly rather than relying on an app.

Want to keep a clearer record of your injection journey? GLP Trackr is free to try for 7 days — available on the App Store and Google Play. Log your sites, track how you feel, and bring better information to your next prescriber appointment.