The short answer
Immunotherapy side effects come from immune inflammation, not cell damage. They can start at any point, including after treatment ends, and need to be reported early so your team can treat them.
Immune-related side effects come from your immune system attacking healthy tissue, so they do not follow the predictable cycle pattern of chemotherapy.
They can begin at any point during and after treatment.
Colitis, pneumonitis, hepatitis, and hormone gland problems are the effects teams watch most closely.
Your team decides how to treat a side effect. Report symptoms early so a small problem does not become a serious one.
On this page
Choose how you want to read this
The whole article, with every detail and caution.
This page is for people having immunotherapy, and for the people who care for them. It explains how its side effects differ from chemotherapy, when they can start, how they are treated, and which symptoms to report.
How immunotherapy side effects are different
Chemotherapy damages fast-dividing cells. That makes its side effects broadly predictable. Nausea in the days after an infusion. Blood counts dipping mid-cycle. Hair loss on a rough schedule.
Immunotherapy works another way. Checkpoint inhibitors take the brakes off your immune system so it can recognize cancer. That same released immune system can also turn on healthy tissue. Those effects are called immune-related adverse events. They follow inflammation, not a cycle calendar.
The practical consequence is simple. You cannot read them off a chart in advance. And waiting until your next scheduled visit to mention something can let a treatable problem become a serious one.
What most people notice
Many people feel reasonably well on immunotherapy. NCI lists rash, diarrhea, and fatigue as the most common effects. Others go through months of treatment with very little to report.
Where inflammation can show up
Inflammation can affect almost any organ. These are the ones your team watches most closely.
- Colitis - bowel inflammation. More stools than usual, stools that wake you at night, cramping, mucus, or blood.
- Pneumonitis - lung inflammation. A new dry cough, breathlessness on stairs you managed last week, chest tightness.
- Hepatitis - liver inflammation. Often picked up on blood tests before you feel anything. Sometimes yellowing of the eyes, dark urine, or an ache under the right ribs.
- Endocrine effects - the thyroid and pituitary glands, and rarely new diabetes. Unusual fatigue, a persistent headache, dizziness on standing, or heavy thirst.
- Skin - rash and itching. Rarely blistering or peeling.
Less often, the pancreas, kidneys, heart muscle, and nerves are affected.
Timing: during and after treatment
Side effects can begin at any point during and after treatment. The timing differs from person to person and by drug, and your team cannot predict it. So a side effect can appear after treatment finishes.
Say you completed immunotherapy in the spring and develop persistent diarrhea in the fall. That is still worth reporting as possibly related. The connection is easy to miss once you are no longer coming in regularly.
How they are treated
Treatment depends on which organ is affected and how severe the problem is. Your team may change or pause your immunotherapy. Ask them what the plan is, and do not stop or start medicines on your own.
Which symptoms to report, and how fast
Some of these cannot wait for a phone call. Call 911 or go straight to an emergency department for any of these. Do not drive yourself:
- chest pain
- breathlessness at rest, or breathing that is getting worse by the hour
- wheeze or swelling of the face, lips or tongue during an infusion
- a sudden severe headache
- confusion, fainting or collapse
- a seizure
- severe belly pain with a hard, tender abdomen
- black, tarry stools, or vomiting blood (MedlinePlus)
Severe weakness with vomiting and dizziness is also an emergency. Tell the staff you are on immunotherapy and show your card.
Call your team right away, at any hour, for any fever, or for blood in the stool (MedlinePlus).
Call the same day for any of these:
- new or increasing diarrhea
- a new cough, or mild breathlessness on exertion
- a headache with light hurting your eyes or gaps in your side vision
- yellow skin or eyes
- very dark urine
- dizziness on standing
If chemotherapy is part of the regimen, a fever is a medical emergency by CDC's reckoning. Ring your team straight away, whatever the hour. Go to an emergency department if you cannot get through.
Call soon, without waiting for your appointment, for rash, itching, unusual tiredness, joint pain, heavy thirst, or anything that simply feels off.
Two habits help. Carry a card or note saying you are on immunotherapy, with your team's number. Show it in any emergency department. Clinicians outside oncology may not think of immune-related effects.
The second habit is to describe change rather than severity: "three loose stools a day, up from one" tells your team far more than "a bit of diarrhea".
Sources
Common questions
I finished immunotherapy three months ago. Can a new symptom still be related?
Yes. NCI says side effects can occur at any point during and after treatment. Tell your oncology team about new diarrhea, cough, breathlessness, severe fatigue, or yellowing of the skin or eyes, even if you have been discharged from active treatment.
Could treating a side effect affect my immunotherapy?
Ask your team how any treatment for a side effect could affect your cancer treatment. Do not stop or start medicines on your own.
Does having side effects mean the treatment is working?
Not reliably. Some people have significant immune-related effects and limited benefit; others have almost no side effects and respond well. Side effects are not a scorecard, and their absence is not a reason to worry.
How do I know if diarrhea is serious enough to call about?
Describe the change rather than judging severity. Three loose stools a day when your normal is one, stools that wake you at night, cramping, or mucus are all worth a same-day call. Any blood in the stool means calling right away, at any hour. Ask your team before taking any over-the-counter antidiarrheal medicine.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Talk with a trained specialist or navigator
Cancer Explained provides educational guidance, but does not replace trained specialists, social workers, or your medical team.
Talk to a trained cancer information specialist
Free, confidential assistance from NCI Cancer Information Service via phone, chat, or email.
Contact your oncology team
Locate after-hours contact numbers, portal messages, or urgent triage phone lines.
Find a patient navigator
Get one-on-one help with appointments, logistics, translation, and care coordination.
Find a genetic counselor
Discuss inherited mutation risk, family history, and genetic testing options.
Find an oncology social worker
Access emotional counseling, family support groups, and mental health resources.
Find a financial navigator
Locate copay assistance foundations, grant programs, and lodging/travel support.
Find a clinical-trial specialist
Search matching studies and speak with NCI trial information specialists.
Get urgent help
Fever of 100.4°F (38°C) or higher during chemo, severe pain, or trouble breathing: call your cancer care team right away, day or night. Call 911 for an emergency.
Know someone who needs this?
Plenty of people are looking for something like this and do not know where to start. If this would help a friend or someone you love, send it on — we have written an opening line so you do not have to stare at an empty message. You can change every word of it.
Your message is written and sent in your own email or messaging app — we never see who you send it to, and nothing is added to any list.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Written by: Cancer ExplainedSources last checked: 2026-07-30 what this meansLast updated: 2026-10-02Next planned review: 2027-01-30
Review details and limits
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Source checked. This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
General education — varies by person. Answers genuinely differ between people. This page explains what commonly varies and points you to your care team for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Words to know
Tap any term to see what it means.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.