Can Weight Loss Injections Cause Cancer?

GLP-1 receptor agonists, the class of medicines that includes semaglutide and tirzepatide, have been studied in large clinical trials and are subject to continuous post-market safety surveillance. At present, no causal relationship between these medicines and cancer in humans has been established by regulators or major health authorities.

Thyroid concerns — a frequently asked question

One area that receives particular attention is thyroid cancer. Animal studies with GLP-1 receptor agonists showed an association with thyroid C-cell tumours in rodents, but this finding has not been replicated in human studies to date. The patient information leaflet for each medicine discusses this, and prescribers are trained to assess thyroid history before prescribing. If you have a personal or family history of thyroid conditions, that is an important conversation to have with your prescriber — not something to manage alone.

Other commonly asked questions

People also ask whether weight loss injections can cause hair loss, constipation, diarrhoea, mood swings, or depression. These are recognised, commonly reported side effects that are well documented. A closer look at the cancer question specifically covers the evidence in more detail. If you are curious about whether weight loss injections can cause kidney stones, that is another topic covered separately. It is worth noting that hair shedding (telogen effluvium) is commonly reported by people losing weight rapidly on any programme — not all side effects are directly caused by the medicine itself.

Mood changes and low mood are also sometimes reported. These are listed in the product information for these medicines, and any persistent or worsening mental health symptoms should be discussed with a healthcare professional promptly — they should never be dismissed or managed without clinical input.

For a broad overview of what is currently known about these medicines, the weight loss injections guide covers the key facts in one place.

When you are on a weekly injectable medicine, keeping a clear record of how you feel over time is genuinely useful — both for your own peace of mind and for conversations with your prescriber.

GLP Trackr's side-effect tracking lets you log symptoms as they happen — nausea, fatigue, mood changes, hair shedding, digestive changes — and review patterns across weeks. Instead of trying to recall how you felt three weeks ago at your next appointment, you have a timestamped log you can share directly. The app also includes a doctor report feature that pulls your logged data into a clear summary, so nothing important gets missed when you sit down with your healthcare team.

If you notice anything that concerns you — particularly anything persistent, severe, or outside what your prescriber mentioned to expect — contact your healthcare professional promptly. GLP Trackr helps you record and communicate what you are experiencing; it is not a substitute for clinical assessment. Any questions about your individual safety, suitability, or whether a symptom needs attention belong with your prescriber or doctor, who knows your full medical history. You can also report unexpected side effects to your national reporting scheme (such as the UK's Yellow Card scheme or the equivalent in your country) as well as to your healthcare professional.

You may also find it helpful to read about B12 injections and weight loss if you are exploring complementary approaches, and our page on weight loss injection costs covers the financial side of the journey neutrally.

Log how you feel, spot your own patterns, and go into every appointment prepared. Download GLP Trackr on the App Store or Google Play and try it free for 7 days.