Are Weight Loss Injections Safe? What the Evidence Says

Both tirzepatide and semaglutide have undergone large clinical trials and regulatory review before being approved for prescription use. Regulatory bodies assess benefits against known risks for the studied population — but approval does not mean risk-free for every individual.

Commonly reported side effects

The most frequently reported effects are gastrointestinal: nausea, vomiting, diarrhoea, constipation, and indigestion. These are generally most noticeable in the early weeks or after a dose adjustment, and many people find they ease over time. Injection-site reactions, headache, fatigue, and dizziness are also commonly reported. You can read factual side-effect information in the official patient information leaflet included with your medicine, or via the electronic Medicines Compendium (eMC).

Groups who need extra care

Certain situations require particular caution and an open conversation with your prescriber before or during treatment:

• Seniors and older adults: age-related factors such as kidney function and other medicines being taken may affect how the injection is tolerated. Your prescriber will factor this in.
• People with thyroid concerns: those with a personal or family history of certain thyroid conditions are generally advised to discuss this with their prescriber before starting, as it is relevant to suitability assessment.
• People who are pregnant, breastfeeding, or trying to conceive: these injections are not currently recommended during pregnancy or breastfeeding. If your circumstances change, contact your prescriber or doctor promptly — do not continue without their guidance.
• People managing diabetes: these medicines can interact with other glucose-lowering treatments and your prescriber will need to monitor and adjust your overall regimen as appropriate.

If you experience severe or persistent symptoms — including severe abdominal pain, signs of an allergic reaction, or significant mood changes — contact your healthcare professional promptly. Any side effects can also be reported to your national reporting scheme (such as the UK's Yellow Card scheme) and to your prescriber.

For a broader look at safety and what these medicines involve, see our guide to weight loss injection safety, or explore the wider topic on our weight loss injections hub.

One of the most practical ways to stay safe on a weekly injection is to keep a clear, consistent record of how your body is responding — and that is exactly where GLP Trackr is built to help.

The app's injection-site tracking and rotation feature logs every injection: the site you used (abdomen, thigh, or upper arm), the date, and the dose. It then suggests your next rotation site automatically, reducing the risk of using the same spot repeatedly, which can cause localised reactions. Alongside that, dose reminders mean you are far less likely to miss a weekly injection or lose track of where you are in your schedule.

If you experience side effects — nausea after a dose, fatigue, or anything else worth noting — the side-effect tracker lets you log symptoms and see patterns over time. That log becomes a genuinely useful conversation-starter at your next prescriber appointment, helping you discuss what you have actually experienced rather than trying to recall it from memory. GLP Trackr is not a substitute for your prescriber's advice — it is a tool that helps you bring better information to that conversation.

Always follow the guidance of your prescriber or doctor. If anything feels severe, persistent, or worrying, reach out to your healthcare professional rather than relying on any app or website to advise you.

Curious about the cost side of things? Our page on weight loss injection pricing covers what to expect in general terms.

Ready to track your injections, rotation sites, and how you feel — all in one place? GLP Trackr is free to start on the App Store and Google Play, with a 7-day trial so you can see how it fits your routine.