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How does chemotherapy affect the cell cycle?

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on Dec 13, 2023.

Official answer


When chemotherapy (cancer drugs) are given to kill cancer cells, they target cells at different phases of the cell cycle. The cell cycle is a series of steps, or phases, each cell takes to become a cell, whether it is a healthy cell or a cancerous cell.

Chemo works by halting cancer cell division, often by interfering with RNA or DNA synthesis, and shrinking the tumor. The cell cycle goes from a resting phase, to an active phase, then to cell division (called mitosis). Chemo kills cells that are either in the resting phase (“cell-cycle non-specific”) or in an actively dividing stage (“cell-cycle specific”).

Your doctor will know when to give your chemotherapy (“chemo”) regimen based on the timing of cell phases. That is why you may receive a chemo regimen as a number of “cycles”, often separated by several weeks. The break in-between treatments also allows your healthy cells to begin to recover.

Why does chemo cause side effects?

Cancer cells typically grow faster than healthy cells. Chemotherapy treatments do not distinguish between healthy cell division and cancer cell division, which means that some healthy cells may be damaged along with the cancer cells during treatment. The damage that occurs to healthy cells during chemotherapy is what leads to some of the common side effects like nausea, hair loss, mouth sores, diarrhea, and low blood cell counts (anemia).

Most people who receive chemotherapy do not have lasting or long-term side effects, but everyone’s treatment journey is different. Cancer cells, which are abnormal cells, do not recover from the chemo treatment. The healthy cells that are damaged during treatment usually recover after chemo is stopped.

You may also receive different cancer medicines used together for a better effect and to help lessen the side effects. For example, other cancer treatments that are not considered “chemo”, such as immunotherapy, hormone therapy and targeted treatments, may be used in addition to your chemotherapy, or at another time. Although these medicines can also cause side effects, they do not typically affect healthy cells like chemotherapy.

Related: The Ferocity of Chemotherapy: Does The End Justify The Means?

Your doctor will attempt to limit the impact of side effects when you receive multiple cancer treatments at the same time. Your doctor may also give you treatments that will help to lessen the side effects of your chemotherapy. Ask your doctor which side effects you may expect during your chemo regimen and how you can manage them.

Related questions

What are the most common chemotherapy drugs?

There are several classes of chemotherapy drugs that your doctor will choose from based on your cancer type and cell cycles. These include:

Some medicines do not fit into a specific category, and this is not a full list of all chemotherapy drugs. Chemotherapy may also be used in addition to surgery, biologic drug therapies, or radiation treatment for the best effect.

Learn more: Common Chemotherapy FAQs from


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