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Medically reviewed by Last updated on Nov 27, 2023.

What is Chemotherapy?

Harvard Health Publishing

Chemotherapy drugs kill cancer cells or prevent them from growing and dividing. Chemotherapy drugs are also called anti-cancer drugs.

Chemotherapy drugs can shrink or limit the size of cancerous tumors. They may also prevent cancer from spreading to other parts of the body.

There are more than 80 anti-cancer drugs. Cancer treatment often requires a combination of two or more different drugs. Cancer specialists design chemotherapy plans based on the cancer being treated and how far the cancer has spread.

Chemotherapy drugs reach almost all parts of the body. This helps to kill cancer cells that have spread from the original site of the cancer. It also allows the drugs to kill cancer cells that are too small to detect on diagnostic tests.

What It's Used For

Chemotherapy is the core treatment for some cancers. This is especially true for cancers that arise from the blood and bone marrow cells. Examples include leukemia, lymphoma and multiple myeloma.

For other cancers, chemotherapy is part of a larger strategy along with radiation and/or surgery. This is often the case for solid tumors such as breast, colon, lung and other cancers arising from an organ.

The goal of chemotherapy is not the same for every type of cancer. The goal also depends upon the stage of cancer. Cancer chemotherapy may be designed to:


Each type of anti-cancer drug produces its own set of side effects. Side effects may vary depending on your body's reaction to the drug. Always ask your doctor about possible side effects before chemotherapy begins.

How It's Done

Anti-cancer drugs can be given in a hospital, clinic, doctor's office or at home. Sometimes the treatment is as easy as swallowing a pill or getting an injection.

Most people receive anti-cancer drugs through a vein. A bag filled with the liquid drug is attached to a tube that is inserted into a vein. The drug slowly drips into the patient's body.

People can receive chemotherapy daily, weekly or monthly.


Doctors may use one or more of the following tests to judge how well chemotherapy is working:

Your doctor may prescribe injections to help boost the production of red and white blood cells. If the counts get too low, you may require blood transfusions.

Doctors also use blood tests to check liver and kidney function. These can be damaged by chemotherapy.


Chemotherapy drugs attack cancer cells. Unfortunately, they also attack normal, healthy cells. This can cause many side effects. Your doctor can help to decrease the severity of many of the side effects of chemotherapy.

Common side effects include:

Chemotherapy inhibits the production of new blood cells. When white cell counts get too low, the body loses the ability to fight infection. That's why a common side effect of chemotherapy is increased susceptibility to infections. These infections can be very serious and often require hospitalization.

Chemotherapy can also affect cells that help blood to clot. This can lead to an increased risk of bleeding.

You may need to adjust your daily routine to deal with side effects. For example, some anti-cancer treatments increase the effects of sunlight on your skin. You may need to modify your outdoor activities or wear protective clothing and sun block.

You may also need to stop taking certain medications that can interfere with some chemotherapy drugs.

Anti-cancer drugs can cause birth defects, particularly if used early in pregnancy. Tell your doctor if you may be pregnant.

Some chemotherapy drugs can cause infertility. Ask your doctor about the impact of chemotherapy on family planning.

When To Call a Professional

Call your doctor if you have any of the following problems during chemotherapy:

Depending on the type of chemotherapy, there may be other side effects to watch for. Your doctor will discuss them with you before treatment starts.

Additional Info

American Cancer Society (ACS)

National Cancer Institute (NCI)

National Comprehensive Cancer Network (NCCN)


Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.