Immunotherapy Side Effects: Managing Your Cancer Treatment Journey
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer
Immunotherapy side effects occur when immune cells mistakenly attack healthy tissue, called an immune-related adverse effect (irAE). Many people receiving immunotherapy experience one, usually mild and easily managed, such as fatigue, itchy rash, diarrhea or low thyroid hormone. They can appear months or years after starting therapy, so tell your provider about any changes, however small. [1]
What the research says
Most side effects of PD-1 and PD-L1 inhibitors are mild. A meta-analysis of 125 trials (20,128 patients) found that 66.0% of patients developed at least one treatment-related adverse event of any grade, and 14.0% developed one of grade 3 or higher. The most common were fatigue (18.26%), itching (10.61%) and diarrhea (9.47%), and hypothyroidism (6.07%) was the most frequent endocrine immune-related event. These figures cover all treatment-related adverse events, not only immune-related ones. (Wang et al., JAMA Oncol, 2019)
Immune-related side effects may signal a response, but this is not proven. A meta-analysis of 30 studies (4,971 patients) found that people who developed irAEs had better overall survival (hazard ratio 0.54) and progression-free survival (0.52) than those who did not. The association was significant for PD-1 inhibitors and for monotherapy, and the authors call for large prospective studies to confirm it. (Zhou et al., BMC Med, 2020)
Why does immunotherapy cause side effects?
Immunotherapy uses your body's immune system to find and destroy cancer cells. Cancer cells are good at slipping past immune defenses, and immunotherapy is designed to give your immune system the boost it needs to rid your body of them. [1]
Any form of treatment has potential downsides, and immunotherapy is no exception. Although it is designed to help your immune system attack cancer cells, immune cells may mistakenly attack healthy tissue. This is called an immune-related adverse effect, or irAE, and it can cause inflammation in healthy tissue that you may feel as one or more side effects. [1]
You may not experience side effects at all. You are more likely to have one if you are taking a combination of immunotherapy drugs or if you have an autoimmune disease, in which your immune system mistakenly attacks healthy tissue. [1]
Common and organ-specific side effects
The most common side effects are mild: fatigue, itchy rash, diarrhea, nausea and vomiting, and decreased thyroid hormone levels. Because your immune system protects your entire body, a supercharged immune system can affect multiple organs and body systems. Most signs and symptoms are minor, but others are serious and need immediate medical attention. [1]
Body system | Potential side effects and symptoms |
|---|---|
Skin | Rash, itchy skin, blisters, cracked skin, painful sores or ulcers, and skin that is more sensitive to sunlight |
Liver | Raised liver enzyme levels, often with no symptoms. Hepatitis can cause jaundice, dark-colored urine, stomach pain on the right side, vomiting and increased bleeding or bruising |
Digestive system | Colitis, which causes diarrhea and can also cause bloody, dark, tarry stools and stomach pain |
Lungs | Pneumonitis (lung inflammation), which is rare and causes coughing, chest pain and shortness of breath |
Thyroid and endocrine system | Too little thyroid hormone (hypothyroidism) or, less commonly, too much (hyperthyroidism). Symptoms can include severe fatigue, weight changes, excess sweating, faster heartbeat, hair loss, dizziness, headaches and constipation |
Brain and nervous system | Rare. Encephalitis (fever, unusual behavior, moodiness, stiff neck, seizures, light sensitivity) or neuropathy (tingling, numbness or weakness in the hands, feet or face) |
Heart and blood vessels | Uncommon. Irregular heartbeat, inflammation of the heart (myocarditis, pericarditis) or of the blood vessels (vasculitis) |
Joints | Arthritis, with joint swelling and joint pain |
Side effects by type of immunotherapy
The side effects you may have depend on the type of immunotherapy you receive. Most research has focused on immune checkpoint inhibitors, but there are several types. [1]
Immune checkpoint inhibitors (ICIs): Help T cells recognize cancer cells as harmful. They may cause fatigue, diarrhea and rash, and more severe side effects include inflammation in organs. [1]
Adoptive cell therapy (T-cell transfer): Your provider changes your T cells in a lab and returns them to your body. Tumor-infiltrating lymphocyte therapy can cause a rare condition called capillary leak syndrome. CAR T-cell therapy can cause cytokine release syndrome (CRS), with fever, headache, fast heartbeat and shortness of breath, and may also cause headaches, confusion and seizures. [1]
Monoclonal antibodies: Lab-made proteins that target specific weaknesses in cancer cells. They can cause flu-like symptoms, abnormal blood pressure, bleeding or blood clots, slow-healing wounds and rash. [1]
Treatment vaccines: Teach your immune system to recognize cancer cells. Side effects may include flu-like symptoms and high blood pressure. [1]
Immunomodulators: Thalidomide, lenalidomide and pomalidomide may cause fatigue and drowsiness, nerve damage (neuropathy) and blood clots, and imiquimod cream can cause skin reactions. [1]
When side effects start, end and how they are managed
There is no set time when side effects begin. It usually takes time for immunotherapy to start working, and side effects may take months or even years to occur, if they occur at all. Some do not appear until over a year after starting therapy. [1]
Most side effects are temporary, but they can linger for some time, even after the medicine is out of your system, because immunotherapy has lasting effects on your immune system. In rare cases, they cause long-term effects. [1]
Speak with your healthcare provider about any symptoms during or after treatment, no matter how small they seem. Often your provider can adjust your treatment or prescribe additional medicines to ease symptoms while preventing complications. They may stop treatment in the short term to give your immune system a cooling period, or prescribe medicines to lessen your immune response, such as steroids and immunosuppressants. They may also suggest lifestyle changes to help you manage symptoms. [1]
Some studies suggest that side effects of immune checkpoint inhibitors may be a sign that treatment is working, but not having side effects does not mean immunotherapy is not helping. [1]
Learn more. For more evidence-based health guides, visit Rinnit.com.
Frequently Asked Questions
Are immunotherapy side effects worse than chemotherapy side effects?
On average, immunotherapy side effects are less severe than those of traditional cancer treatments such as chemotherapy. They are different, though. They are related to inflammation, they vary from person to person, and some are serious and need prompt medical care.
Can I take over-the-counter medicine for my side effects?
Ask your oncology team before taking any new medicine, including over-the-counter products. Your provider can often adjust your treatment or prescribe additional medicines to ease symptoms while preventing complications.
How common is cytokine release syndrome (CRS)?
CRS is associated with CAR T-cell therapy, in which the immune system releases proteins called cytokines that ramp up the immune response. It can cause fever, headache, fast heartbeat and shortness of breath, and your healthcare provider can help you manage the symptoms.
Will my side effects go away if I stop treatment?
Most side effects are temporary, but they can linger for some time even after the medicine is out of your system, because immunotherapy has lasting effects on your immune system. In rare cases, side effects cause long-term effects.
Does having side effects mean the treatment is working?
Some studies suggest that side effects of immune checkpoint inhibitors may be a sign that the treatment is working, but not having side effects does not mean immunotherapy is not helping. More research is needed to understand the relationship.
Can I go in the sun during immunotherapy?
Immunotherapy can make your skin more sensitive to sunlight. Ask your care team how to protect your skin.
What is pneumonitis?
Pneumonitis is inflammation of the lungs. It is a rare side effect of immunotherapy, and symptoms include coughing, chest pain and shortness of breath. Tell your provider about these symptoms promptly.
Is diarrhea a serious concern during treatment?
Diarrhea can be. Colitis, an inflammation of the colon, causes diarrhea and can also cause bloody, dark, tarry stools and stomach pain. Tell your provider about any changes in your bowel habits.
Can immunotherapy affect my mood or behavior?
Rarely, immunotherapy can cause encephalitis, an inflammation of the brain that may cause fever, unusual behavior, moodiness, a stiff neck, seizures and sensitivity to light. Report these symptoms right away.
Should I change my diet to reduce side effects?
Your provider may suggest lifestyle changes to help you manage symptoms. Discuss any major diet changes or supplements with your care team before starting them.
How do doctors treat severe side effects?
Your provider may stop treatment for a short time to give your immune system a cooling period, or prescribe medicines to lessen your immune response, such as steroids and immunosuppressants.
Can I still work while undergoing immunotherapy?
Some people can, but it depends on how you feel. Fatigue is one of the most common side effects, so talk with your care team about your schedule and energy levels.
What is an irAE?
The abbreviation irAE stands for immune-related adverse effect, the term for a side effect that happens when immune cells mistakenly attack healthy tissue and cause inflammation.
How will I be monitored for side effects?
Your care team will explain your monitoring plan. Immunotherapy can raise liver enzyme levels, usually without symptoms, so tell your provider about any changes you notice.
What is the most important thing to remember?
Tell your provider about any symptoms you notice during or after treatment, no matter how small or unimportant they seem. Often your provider can adjust treatment or prescribe medicines to ease symptoms and prevent complications.
Related Reading
Immunotherapy for Cancer: How It Works and What to Expect explains how cancer immunotherapy works and the main types used.
CAR T-Cell Therapy: How It Works, Side Effects, and Recovery explains CAR T-cell therapy and its specific side effects.
Pneumonitis: What It Is, Causes, and the Treatment Pathway That Protects Your Lungs explains lung inflammation, a serious possible immunotherapy side effect.
Corticosteroids (Glucocorticoids): Uses, Types, Side Effects and When to Call Your Doctor explains steroid medicines often used to calm immune side effects.
References
Cleveland Clinic. Immunotherapy Side Effects. Cleveland Clinic. Last updated September 6, 2022. https://my.clevelandclinic.org/health/diseases/21096-immunotherapy-side-effects
Wang Y, et al. Treatment-Related Adverse Events of PD-1 and PD-L1 Inhibitors in Clinical Trials: A Systematic Review and Meta-analysis. JAMA Oncol. 2019;5(7):1008-1019. PMID 31021376. https://doi.org/10.1001/jamaoncol.2019.0393
Zhou X, et al. Are immune-related adverse events associated with the efficacy of immune checkpoint inhibitors in patients with cancer? A systematic review and meta-analysis. BMC Med. 2020;18(1):87. PMID 32306958. https://doi.org/10.1186/s12916-020-01549-2
Medical disclaimer
This article is for general educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. If you are receiving cancer treatment, always follow the guidance of your oncology team and contact them about any new symptoms.
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