Why can immunotherapy side effects cause persistent fatigue?

Persistent Fatigue is a common presentation of Immunotherapy Side Effects. Immunotherapy can stimulate immune activity beyond the tumour, sometimes causing inflammation in organs such as the thyroid or adrenal glands. Changes in these hormones can affect energy, concentration, temperature tolerance, appetite, or blood pressure.

Cancer itself, pain, emotional strain, reduced activity, infection, medicines, dehydration, and changes in sleep can also contribute. Fatigue may continue after treatment pauses while inflammation settles or hormone replacement is adjusted, so a continuing symptom deserves assessment rather than being dismissed as an expected treatment effect.

Tell your oncology team when the fatigue began, whether it is worsening, how it changes your daily activities, and whether rest helps. Your team may review medicines, hydration, nutrition, sleep, and mood, and may arrange blood tests to check blood counts, thyroid function, hormone levels, or signs of inflammation.

Use gentle activity within your limits, plan demanding tasks for the time of day when you have more energy, take regular fluids if your team has not restricted them, and keep a simple record of symptoms. Do not start hormone treatment, iron, stimulants, or supplements without medical advice.

Contact your oncology team promptly for rapidly worsening fatigue, faintness, new confusion, severe weakness, persistent vomiting or diarrhoea, a severe headache, vision changes, chest pain, shortness of breath, a fast or irregular heartbeat, or an inability to keep fluids down. These symptoms can signal a significant immune-related problem or another condition needing timely treatment.

Seek emergency help for severe breathing difficulty, collapse, new one-sided weakness, or loss of consciousness. Keep your immunotherapy treatment card or medication list available, and tell the clinician when your last treatment was given.

Could my fatigue be related to thyroid or adrenal changes, anaemia, infection, or another medicine? Which tests should check these causes? Should I pause, delay, or change immunotherapy? What symptoms should prompt a same-day call, and how should I pace activity while we investigate?