Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Chemotherapy Side Effects


Robert Peter Gale

, MD, PhD, DSC(hc), Imperial College London

Reviewed/Revised Sep 2022
Topic Resources

Chemotherapy refers to drugs given to kill or slow the growth of cancer cells. However, because chemotherapy drugs work throughout the body (for example on all cells in a particular stage of development), healthy cells are attacked as well as cancerous ones. Because healthy cells are also damaged during chemotherapy, side effects are likely.

Chemotherapy commonly causes nausea, vomiting, loss of appetite, weight loss, fatigue, and low blood cell counts that lead to anemia Overview of Anemia Anemia is a condition in which the number of red blood cells is low. Red blood cells contain hemoglobin, a protein that enables them to carry oxygen from the lungs and deliver it to all parts... read more and increased risk of infections. People also often lose their hair, but other side effects vary according to the type of drug.

Gastrointestinal Effects

Gastrointestinal (digestive tract) effects are very common and include

  • Loss of appetite

  • Nausea and vomiting

  • Diarrhea

These effects also may be caused by the cancer itself

Loss of appetite is common and may cause weight loss. People who lose more than 10% of their ideal body weight do not do as well as those who are able to maintain their weight or lose less weight. Doctors encourage people to maintain good nutrition. There are several drugs that increase appetite, but it is not clear whether they actually can reverse weight loss, improve quality of life, or prolong survival.

Nausea and vomiting greatly harm quality of life. People often think all cancer drugs cause nausea and vomiting, but these symptoms are more likely with certain drugs and with certain situations. Nausea and vomiting can usually be prevented or relieved with drugs (antiemetics), particularly with granisetron, ondansetron, or aprepitant. Doctors may give these drugs before a dose of chemotherapy as well as to treat nausea and vomiting after it has started. Nausea may also be reduced by eating small meals and by avoiding foods that are high in fiber, that produce gas, or that are very hot or very cold. In some states, marijuana can be prescribed to relieve nausea and vomiting caused by chemotherapy.

Diarrhea is common after treatment with chemotherapy drugs or with targeted therapy drugs (and after radiation therapy). Diarrhea is usually treated with the drug loperamide

Low Blood Cell Concentrations

Cytopenias, a deficiency of one or more types of blood cell, can develop because of the toxic effects that chemotherapy drugs have on the bone marrow (where blood cells are made). For example, a person may develop abnormally low numbers of

Red blood cells carry oxygen from the lungs to all the cells of the body. Without enough red blood cells, people may be pale or have fatigue or weakness. People with more severe anemia may have dizziness, thirst, sweating, or even shortness of breath and chest pain. If anemia is severe, packed red blood cells can be transfused. A red blood cell growth factor, erythropoietin, also can be given, but transfusion is preferred because there is less risk of a blood clot.

A person with neutropenia is at increased risk of developing an infection because white blood cells are an essential defense against infection. A fever higher than 100.4° F (38° C) in a person with neutropenia is treated as an emergency. Such a person must be evaluated for infection and may require antibiotics and even hospitalization. White blood cells are rarely transfused because, when transfused, they survive only a few hours and produce many side effects. Instead, certain substances (such as granulocyte-colony stimulating factor) can be administered to stimulate white blood cell production.

Platelets are small cell-like particles in the blood that help it to clot when there is a cut or broken blood vessel. A person without enough platelets (thrombocytopenia) is likely to bruise and bleed easily. If thrombocytopenia is severe, people may have severe digestive tract bleeding Gastrointestinal Bleeding Bleeding may occur anywhere along the digestive (gastrointestinal or GI) tract, from the mouth to the anus. Blood may be easily seen by the naked eye (overt), or blood may be present in amounts... read more Gastrointestinal Bleeding or bleeding into their brain. Platelets can be transfused to treat or help prevent bleeding.

Chemotherapy-Induced Thrombocytopenia

Mouth Sores

Many people develop inflammation or even sores of the mucous membranes, such as the lining of the mouth. Mouth sores are painful and can make eating difficult. Various oral solutions (usually containing an antacid, an antihistamine, and a local anesthetic) can reduce the discomfort. On rare occasions, people need nutritional support Overview of Nutritional Support Many undernourished ( see Undernutrition) and critically ill people need additional nutrition (nutritional support). Artificial feeding, which uses commercial nutrient mixtures rather than food... read more by a feeding tube that is placed directly into the stomach or small intestine or even by vein.


Depression may be the result of cancer therapy as well as the cancer itself.

Organ Damage and Other Cancers

Sometimes chemotherapy drugs may damage other organs, such as the lungs, heart, or liver. For example, anthracyclines (such as doxorubicin), a type of topoisomerase inhibitor, cause heart damage when used in high total doses.

People treated with chemotherapy, particularly alkylating agents, may have an increased risk of developing leukemia Overview of Leukemia Leukemias are cancers of white blood cells or of cells that develop into white blood cells. White blood cells develop from stem cells in the bone marrow. Sometimes the development goes awry... read more several years after treatment. Some drugs, especially alkylating agents, cause infertility in some women and in most men who receive these treatments.

Tumor Lysis Syndrome and Cytokine Release Syndrome

Tumor lysis syndrome may occur after chemotherapy because, when cancer cells are killed, they may release their contents into the bloodstream. These contents may damage the kidneys or heart. Tumor lysis syndrome occurs mainly in acute leukemias Overview of Leukemia Leukemias are cancers of white blood cells or of cells that develop into white blood cells. White blood cells develop from stem cells in the bone marrow. Sometimes the development goes awry... read more and non-Hodgkin lymphomas Non-Hodgkin Lymphomas Non-Hodgkin lymphomas are a diverse group of cancers of types of white blood cell called lymphocytes. Often, lymph nodes in the neck, under the arms, or in the groin enlarge rapidly and painlessly... read more Non-Hodgkin Lymphomas but can also occur after treatment of other types of cancer. Sometimes doctors are able to prevent tumor lysis syndrome by giving allopurinol before and during chemotherapy. Doctors may also give fluids by vein to cause the kidneys to excrete these toxic products quickly.

Cytokine release syndrome is related to but distinct from the tumor lysis syndrome. Cytokine release syndrome occurs when large numbers of white blood cells are activated and release inflammatory substances called cytokines. It is a frequent complication of cell-based therapies such as those using CAR-T-cells T cells One of the body's lines of defense ( immune system) involves white blood cells (leukocytes) that travel through the bloodstream and into tissues, searching for and attacking microorganisms and... read more T cells and some monoclonal antibodies Monoclonal antibodies Immunotherapy is used to stimulate the body's immune system against cancer. These treatments target specific genetic characteristics of the tumor cells. The genetic characteristics of tumors... read more . Symptoms include fever, fatigue, loss of appetite, muscle and joint pain, nausea, vomiting, diarrhea, rashes, rapid breathing, headache, confusion, and hallucinations. In general, treatment for mild cytokine release syndrome is supportive and involves relieving symptoms like fever, muscle pain, or fatigue. Oxygen therapy, fluids and drugs to raise blood pressure, and drugs to decrease inflammation may be needed in people with more severe cytokine release syndrome.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Granisol, Kytril, Sancuso, Sustol
Zofran, Zofran in Dextrose, Zofran ODT, Zofran Solution, Zuplenz
Anti-Diarrheal, Imodium A-D, Imodium A-D EZ Chews , K-Pek II
Adriamycin, Adriamycin PFS, Adriamycin RDF, Rubex
Aloprim, Zyloprim
quiz link

Test your knowledge

Take a Quiz!