How does chemotherapy work?

PDF download is not available for Arabic and Urdu languages at this time. Please use the browser print function instead

Chemotherapy works by damaging cells as they are dividing. Find out how chemotherapy reaches the cancer cells, why there are so many different chemotherapy medications and what 'protocol' means in terms of treatment.

Key points

  • Cells reproduce by dividing when our body needs to make new cells.
  • Some chemotherapy drugs work by damaging cells as they are dividing.
  • Chemotherapy medications travel through the blood to reach different parts of the body.
  • Different chemotherapy medications work in different ways. The type of chemotherapy given will depend on the type of cancer.

​How does chemotherapy work?

Cells reproduce by dividing so that one cell becomes two, and then two cells become four, and then eight, and so on. Normal cells only reproduce when our bodies need new cells, for example to allow us to grow or replace cells that die.


Some chemotherapy drugs work by damaging cells as they are dividing and reproducing. Cancer cells behave differently than normal cells and often divide more frequently. This means they are sensitive to the chemotherapy drugs that interfere with cell division or reproduction. Although chemotherapy can damage normal or healthy cells too, non-cancerous cells are usually able to repair themselves.

How does chemotherapy reach the cancer cells?

Chemotherapy medications travel through blood and can usually reach most of the different parts of the body. The blood carries the medication to the site of the cancer and to any cancer cells that have spread to other parts of the body.

Why are there so many different chemotherapy drugs?

Each chemotherapy drug damages cancer cells in a different way. For example, one chemotherapy drug might damage different parts of the cells than another one does, or it might damage the cells at different points in the process of dividing. This is why different chemotherapy drugs are used to treat different types of cancer. It is also why treatment might involve more than one type of medication.

You might sometimes hear your health-care team talk about a chemotherapy "protocol". This is a chemotherapy treatment plan designed to treat your type of cancer. You will learn a lot more about your chemotherapy when you start your protocol. The assent forms contain information about how the medication works and any side effects you may expect.

Useful resources

AboutKidsHealth - Chemotherapy at home: Safely handling and giving medications

Canadian Cancer Society - Chemotherapy

American Cancer Society - Chemo – What it is, How it helps

Cancer Research UK - How chemotherapy works

Macmillan Cancer Support (from the United Kingdom) - Chemotherapy explained​

Last updated: September 3rd 2019