Care Guide: Digestive System Side Effects

Our staff has developed a reference on side effects that affect the digestive system. Use our information to help identify and prevent mouth sores, diarrhea, constipation, nausea, vomiting and dehydration.

Mouth Sores

When the patient is receiving chemotherapy or radiation, they may have increased sensitivity, redness, white patches or open sores in the mouth or on the lips. This is caused when chemotherapy and radiation temporarily destroy the fastest growing cells in the body along with cancer cells. Mucous membranes (protective linings inside of the nose, mouth and gastrointestinal tract) and hair follicles are also cells that reproduce quickly. Good mouth care can help to prevent mouth sores:

  • Brush teeth gently after each meal with a soft brush, toothette or soft cloth wrapped around your finger
  • Use mouthwash if brushing cannot be tolerated
  • Rinse the mouth after each meal
  • Avoid mouthwash with alcohol, as it may sting
  • If mouthwash is irritating, rinse with water
  • Contact your doctor before using over-the-counter numbing gels or rinses for pain control
  • If mouth pain remains uncontrolled, the patient may need to be admitted for IV pain control
  • Eat soft, non-spicy foods like mashed potatoes and gravy, ice cream, jello, custard, scrambled eggs, yogurt or cottage cheese
  • Spicy foods are not harmful if they are what the patient prefers
  • Avoid foods with rough edges like chips, toast, or taco shells if they are difficult to eat
  • Cold or room temperature foods may feel better to a sore mouth than warm foods
  • Straws may be helpful
  • Involve your child in decisions about food choices
  • If the patient refuses to drink or swallow, contact your treatment team


Diarrhea is loose or watery stool occurring more often than the patient normally goes in a day. It may be caused by chemotherapy, radiation therapy or infection. If the patient has diarrhea, your health care team will need to know about the color, consistency, amount and number of stools per day. To ease bowel irritation:

  • Avoid spicy, fried or fatty foods
  • Feed the patient their normal diet as tolerated, unless they are vomiting

Call the treatment team if the patient:

  • Has more than eight diarrhea stools in 24 hours
  • Has diarrhea that does not improve in 24 hours
  • Is vomiting
  • Does not urinate in eight hours
  • Is not drinking


Constipation is defined as no stool in 3 to 4 days, or hard, formed stools that may cause abdominal pain or rectal bleeding. This can be caused by eating less fiber, drinking less fluids, decreased physical activity, chemotherapy (such as vincristine or vinblastine) or certain pain medications.

Correcting Constipation

  • Encourage plenty of fluids, especially fruit juices
  • Minimize drinks with caffeine
  • Increase the amount of fiber in the patient’s diet by including fresh fruits, vegetables and whole grains
  • Encourage more exercise through play or physical activity

Call the treatment team if our suggestions do not help. Sometimes a stool softener or laxative will need to be ordered to prevent constipation. Do not use a stool softener or laxative unless the doctor orders it. Do not use rectal suppositories.

Nausea & Vomiting

Nausea and vomiting are caused by irritation of the stomach lining or by direct stimulation of the nausea and vomiting centers of the brain, caused by certain medications or by infections such as the flu virus. Most medication-induced nausea and vomiting begin within one to two hours after taking a medicine. Some medications cause delayed nausea and vomiting that can begin several hours after receiving the medication. The length of time of nausea and vomiting can vary from minutes to hours. The patient may not have the same symptoms as another patient receiving the same medicine.

  • If the patient is vomiting, give small frequent feeds of clear liquids
  • Return to the patient’s normal diet as tolerated

Episodes of severe nausea and vomiting lasting longer than 12 hours should be reported to the treatment team.

Anticipatory Nausea & Vomiting

Sometimes patients develop what is called anticipatory nausea and vomiting and may begin to feel nauseated or start vomiting the night before chemotherapy. The patient cannot control this and needs your support and understanding. If the patient develops this type of anticipatory nausea and vomiting, discuss it with your treatment team.


Many different anti-nausea medicines (antiemetics) are available to treat nausea and vomiting caused by chemotherapy and radiation therapy. Sometimes a combination of two or three medications may be used. Your treatment team will work with you and the patient to discover which medications work best.

Medication Side Effects

Drowsiness is a side effect of some medications used to control nausea and vomiting. Some older children may refuse the anti-nausea medications because they don’t like the drowsiness. Control is an important issue at this age and it is wise to respect the patient’s wishes.


Dehydration is a state in which the body has lost excessive amounts of fluid. This may be caused by diarrhea, vomiting or fever accompanied by inadequate intake of fluid. Watch the patient for signs and symptoms of dehydration, including:

  • Dry mouth
  • Little or no tears produced while crying
  • Sunken eyes
  • Sunken soft spot on the top of a baby’s head
  • Less than six wet diapers in 24 hours for babies
  • Fewer trips to the bathroom for older patients
  • A period of 6 to 8 hours in which the patient does not urinate
  • Decreased energy or activity

Dehydration can be mild, moderate or severe. Contact your treatment team right away if you think that the patient is dehydrated.