Cancer: Facts About Nausea and Vomiting

Treatments for cancer, and sometimes the cancer itself, may cause you to feel sick to your stomach. You may feel nauseated or vomit. You may worry about these side effects before you start treatment. Or you may have very little nausea or vomiting, or none at all. If you do feel sick, medicines and home treatments can help.

Causes of nausea and vomiting

Nausea and vomiting can be caused by:

  • Chemotherapy.
  • Radiation therapy.
  • Your cancer itself.
  • Another illness.
  • Medicines you might be taking.

Nausea or vomiting caused by chemotherapy

Chemotherapy can cause several types of nausea and vomiting:

  • Acute nausea or vomiting, which happens when you start chemotherapy. It may start right after treatment. It is often at its worst within 5 to 6 hours after your treatment.
  • Delayed nausea or vomiting, which usually starts more than a day after your chemotherapy. It can last for 6 to 7 days. It is usually at its worst 2 to 3 days after your treatment.
  • Anticipatory nausea or vomiting, which is triggered by your memory of a bad experience. You may have this type of nausea or vomiting before or during chemotherapy.

Sometimes you may vomit even though you are taking medicines that help keep you from feeling sick.

  • You may have breakthrough vomiting if you are not taking a high enough dose of nausea and vomiting medicine.
  • You may have refractory vomiting if your nausea and vomiting medicine stops working altogether.

Radiation-induced nausea and vomiting

Radiation therapy can cause nausea and vomiting. The symptoms may start half an hour after treatment, and last several hours. How sick you feel depends on:

  • What part of your body is being treated. You are most likely to feel sick if you are having radiation therapy in the area of your digestive system (for example, your stomach or small intestine) or your brain.
  • How much of your body is being treated. The larger the area, the more likely you will feel sick.
  • How much radiation is used. The higher the dose of radiation, the more likely you will feel sick.
  • If you are also being treated with chemotherapy. If you have both radiation therapy and chemotherapy, you are more likely to feel sick to your stomach.
  • Your radiation treatment schedule. If your treatments are close together—every day, for instance—your body does not have as much time to recover.

What happens if nausea and vomiting are not controlled?

Vomiting too much can cause you to get dehydrated. Dehydration causes problems with electrolytes, which are minerals found naturally in the body. These minerals keep the body's balance of fluids at the right level. Problems with your electrolyte balance can affect the way your body functions. Dehydration can be mild or severe and can cause:

  • Increased thirst and a dry mouth.
  • Weakness.
  • Dizziness.
  • Palpitations (the uncomfortable feeling that your heart is beating fast or irregularly).
  • Confusion.
  • Feeling slow or sluggish.
  • Fainting.
  • Not sweating even though you may be warm.
  • Urinating very little or not at all.

When are nausea and vomiting an emergency?

Call 911 anytime you think you may need emergency care. For example, call if:

  • You passed out (lost consciousness).
  • You vomit blood or what looks like coffee grounds.

Call your doctor now or seek immediate medical care if:

  • You cannot stop vomiting.
  • You get dizzy or weak.
  • You have signs that you need more fluids. You have sunken eyes and a dry mouth, and you pass only a little urine.
  • You have a lot of pain and cramps.
  • Your belly swells.
  • You are vomiting so much that you cannot keep your medicine down.
  • You have any problems with your medicine.

Communicating with your doctor

Before you start treatment, talk to your doctor about nausea and vomiting. Ask the following questions:

  • Will my cancer treatment cause nausea and vomiting?
  • Are there ways to control my nausea and vomiting?
  • How will you decide how to treat my nausea and vomiting?
  • Do these treatments have any side effects?
  • What can be done if the treatments don't work?
  • Can I do anything to help myself?

Keep track of when you have symptoms and what you do to help relieve them. Refer to the record when you talk with your doctor.