Chemotherapy (sometimes called chemo) uses drugs to kill cancer cells. Chemotherapy is used to treat many types of cancer. Chemotherapy drugs can be given on their own or they can be given together in a combination (called combination chemotherapy). Chemotherapy may be given alone or with other treatments, such as radiation therapy or targeted therapy. Chemotherapy is also given in high doses as part of a stem cell transplant.

How chemotherapy works

Chemotherapy works best on cells that are actively growing and dividing. Cancer cells tend to grow and divide quickly so this makes them good targets for chemotherapy. But chemotherapy can’t tell the difference between cancer cells and normal cells. Some normal cells, such as those in hair follicles and the lining of the digestive system, also tend to grow and divide quicker than other cells in the body. Chemotherapy can affect these cells as well. This is why some people lose their hair or vomit and have diarrhea. Normal cells can usually repair the damage over time, and these side effects tend to go away once you are finished chemotherapy treatment.

How chemotherapy is used

Chemotherapy may be used alone to treat cancer or with other treatments such as surgery or radiation therapy. It may be used before surgery to shrink a tumour or after surgery to destroy any cancer cells that remain and to prevent the cancer from coming back. Chemotherapy may also be used to relieve symptoms, improve quality of life and extend life for people with advanced cancer (called palliative chemotherapy).

Most chemotherapy is used as a systemic therapy. This means that the drugs travel around through the bloodstream and can attack cancer cells almost anywhere in the body.

Deciding which drugs to use

Chemotherapy drugs used to treat cancer are prescribed by a medical oncologist. This doctor will discuss with you the chemotherapy drugs that are most likely to work and decide the dose, schedule and length of treatment. Chemotherapy drug treatment plans, called regimens, depend on:

  • the type of cancer
  • the stage of the cancer
  • your age
  • your overall health and if there are other health problems (such as heart, liver or kidney diseases)
  • the types of cancer treatment you’ve already had or your planned treatment
  • your preference


Chemotherapy and other drugs used to treat cancer may not kill all the cancer cells the first time they are given. Some cancer cells may survive and continue to grow. Chemotherapy and other drugs are given according to a plan or schedule designed to kill as many cancer cells as possible. Chemotherapy and other drug treatment is often repeated and is usually given at regular intervals called cycles. Each cycle of these drugs is usually followed by a rest period (such as several days or weeks) when no treatment is given. The rest period allows normal cells to recover.


The length, timing and number of cycles of chemotherapy or other drugs depends on the combination of drugs used and the type of cancer. The medical oncologist usually sets the schedule when treatment starts. The schedule may also be decided later, based on how well the drug is working and how the body tolerates it.

Types of chemotherapy

There are many chemotherapy drugs that are grouped into classes depending on how they work. Combining chemotherapy drugs from different classes can make the treatment work better because the different drugs attack cancer cells at different points in their growth cycle. It may also prevent resistance and help lower the chance of cancer coming back (recurrence).

Some types of chemotherapy include:

DNA-damaging agents are also called alkylating agents. They stop cells from dividing by changing the cell’s DNA so it can’t be copied. Because cancer cells grow and divide quickly, they end up dying because they don’t have time to repair the damaged DNA.

Antimetabolites act like the building blocks of DNA or RNA that cancer cells need to grow and survive. When a cancer cell uses the antimetabolite chemotherapy drug instead of their own substances, the DNA is damaged and the cell dies.

Antimitotics block the process of cell division called mitosis so cells can’t divide and multiply.

Antitumour antibiotics bind to DNA so it can’t work properly. This causes the cell to die. These drugs are different than antibiotics used to treat infection.

DNA-repair enzyme inhibitors prevent the normal repair of DNA damage inside the cell. These chemotherapy drugs attack the enzymes that normally repair damage to DNA. If a cancer cell can’t repair damage to DNA, it dies.

Going for chemotherapy

Your chemotherapy treatment will be planned by a medical oncologist, a cancer specialist who oversees drug therapies. They work with other members of the healthcare team to plan and deliver treatments.

Chemotherapy treatments may be given every day, every week or every month. Chemotherapy drugs are often given at regular intervals called cycles. For example, a cycle may be treatment for 3 days followed by a rest period of 25 days. The rest period gives the body a chance to build new healthy cells and regain its strength. The course of treatment, which is the entire chemotherapy treatment from start to finish, may last 3 months or longer. So you may have 4 or more cycles of treatment in your course of treatment. Your healthcare team will tell you how long they expect your treatment to last.

Your healthcare team will tell you what you can eat and drink and what you should avoid while taking chemotherapy. Tell your doctor what medicines you take, including prescription drugs, vitamins and supplements such as herbs.

Before treatment begins

Before starting chemotherapy, your healthcare team may suggest that you get your teeth cleaned and checked. This is because chemotherapy can lead to a sore and dry mouth and it can also lower your body’s ability to fight infection.

Chemotherapy can also be hard on your heart, so your team may suggest that you have an echocardiogram to test how well your heart is working.

Chemotherapy can also affect your fertility (the ability to get or stay pregnant or get someone else pregnant). Before you start cancer treatment, talk to your healthcare team if you want to have children in the future. There may be ways to protect your fertility before or during treatment.

If you are getting chemotherapy through a vein (intravenously, IV) you may have surgery to place a soft, flexible catheter (called a central venous catheter or port). These are used to deliver the drugs if you need to have chemotherapy over a long period of time. It prevents you from getting poked with a needle every time.

Medicines to help reduce side effects, such as nausea and vomiting, are often given about 20 to 30 minutes before chemotherapy.

Where chemotherapy is given

Where chemotherapy treatment takes place depends on your situation, the drugs being used and the services available in the community. Treatment may be given:

  • at a cancer clinic or hospital
  • at home
  • in a doctor’s office

Most people receive chemotherapy as an outpatient and do not need to stay overnight at a clinic or hospital. You may need to stay at the hospital if the treatment has to be given for 24 hours or longer. Some people stay at the hospital when they first start chemotherapy so the healthcare team can watch for side effects.

How chemotherapy is given

Chemotherapy can be given in different ways, which are called routes of administration. The way chemotherapy is given depends on the type of drug, the goal of treatment and the type and location of the cancer.

Most chemotherapy drugs are given directly into a vein (intravenous) using a needle or a small plastic tube called a catheter. This allows the drugs to go directly to the bloodstream where they can be carried to the tumour and any cancer cells that have spread from the tumour. Sometimes a pump is used to control how fast the chemotherapy drugs are given.

Other ways that chemotherapy is given include:

  • by mouth, such as with pills or capsules (oral chemotherapy)
  • into the cerebrospinal fluid (CSF) surrounding the spinal cord (intrathecal chemotherapy)
  • into the CSF within the brain (intraventricular chemotherapy)
  • into an artery (intra-arterial chemotherapy)
  • into a body cavity, such as the abdomen or chest (intracavitary chemotherapy)
  • into a muscle (intramuscular chemotherapy)
  • directly into a tumour (intralesional chemotherapy)
  • using a cream or ointment on the skin (topical chemotherapy)

Safety precautions

Chemotherapy is strong, powerful medicine that can harm and destroy cells. It must be handled safely and disposed of carefully. Healthcare staff may wear gloves, a mask, protective goggles or a gown to avoid direct contact with the drugs. Some drugs (described as vesicants) can also damage the tissues if they leak out of the vein, so a member of the healthcare team may stay with you when the drugs are given.

You and your caregivers will also need to be careful when handling bodily fluids since chemotherapy drugs can also be passed through urine, stool and vomit for 48 hours after treatment.

Your healthcare team will give you instructions about:

  • what precautions to take when using the toilet
  • what to do if your clothes or linens get bodily fluids on them
  • how to handle chemotherapy drugs if you are taking them at home
  • whether you should avoid having sex or when it is safe to have sex
  • any precautions you should take while having sex (including oral sex)

It’s important to avoid getting pregnant or getting someone pregnant during treatment. This is because some chemotherapy drugs can cause gene mutations or birth defects in a developing fetus. A woman may still be fertile while she is receiving chemotherapy, even if her menstrual cycle becomes irregular or stops. Talk to your healthcare team about the best birth control method for you and your partner.

Since chemotherapy drugs can weaken your immune system, you should also:

  • Wash your hands often.
  • Protect yourself when around other people who are sick to help prevent infection. In some cases, your doctor may suggest that you avoid people who are sick until they feel better.
  • Practise food safety.

Medicines to manage side effects

Sometimes medicines are given after each chemotherapy treatment to help with delayed side effects, such as nausea, vomiting or diarrhea. These medicines are usually taken by mouth and may be continued for a few days after chemotherapy. Your healthcare team will tell you how often you will need to take the supportive care medicines to help you deal with your symptoms.

Monitoring during chemotherapy

Because chemotherapy affects rapidly dividing cells, blood cells – which grow quickly – can also be affected. You will have regular blood tests to check the level of blood cells throughout the course of treatment. You may have a complete blood count (CBC) or other tests before each chemotherapy treatment.

A drop in blood cell counts shows that the chemotherapy drugs are working. A small drop in blood cell counts is usually not harmful. If blood cell counts stay within a normal range, then it is safe to keep giving chemotherapy drugs. But if the count for one type of blood cell is too low, the doctor may have to adjust the dose or postpone treatment for a while.

You may have more blood tests, x-rays or other imaging tests to see how well the treatment is working.

Resistance to chemotherapy

Some types of chemotherapy may not work well to destroy certain types of cancer. These cancer cells are resistant to the treatment. Resistance to chemotherapy can happen right from the beginning of treatment or it may happen over time. So a drug that was working to destroy cancer cells may stop working. Your doctor will prescribe a different drug or treatment if you develop resistance to a certain type of chemotherapy.

After chemotherapy

In addition to safety precautions, the healthcare team will tell you about what to eat or drink, when you can be physically active or return to work. Some people may find they need extra rest for a while after treatment is finished.

Chemotherapy can weaken your immune system. During and for some time after treatment, chemotherapy can affect blood cells that help protect the body from illness, infection or excessive bleeding. Wash hands often, especially after using the toilet and before preparing food.

Expert review and references

Taking oral chemotherapy at home

Your cancer treatment may include taking oral chemotherapy (chemo) at home. These are drugs you swallow to treat cancer. They may be tablets or capsules.

Side effects of chemotherapy

Chemotherapy drugs kill cancer cells, but they can also damage healthy cells. This damage to healthy cells causes side effects. Different cells and tissues in the body tolerate chemotherapy differently. Chemotherapy drugs have the greatest effect on rapidly dividing cells, such as blood cells in the bone marrow, cells lining the mouth and gastrointestinal (GI) tract and hair follicle cells.

Sources of drug information

The following websites provide information about specific chemotherapy, biological therapy, hormonal therapy or other drugs, including doses, side effects, possible precautions and more. These information sheets may not contain all known information about a drug. Talk to your doctor, pharmacist or nurse to find out more about a particular drug.

Medical disclaimer

The information that the Canadian Cancer Society provides does not replace your relationship with your doctor. The information is for your general use, so be sure to talk to a qualified healthcare professional before making medical decisions or if you have questions about your health.

We do our best to make sure that the information we provide is accurate and reliable but cannot guarantee that it is error-free or complete.

The Canadian Cancer Society is not responsible for the quality of the information or services provided by other organizations and mentioned on, nor do we endorse any service, product, treatment or therapy.

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