How Chemotherapy Causes Diarrhoea in Cancer Patients


Cancer occurs when grow in an abnormal way. They divide uncontrollably, invade neighbouring tissues and sometimes spreading to other parts of the body.


There are more than 100 different types of . Cancer can affect almost every part of the body including the tongue, lungs and skin. While science has been able to find out several risk factors for different types of cancer, its exact cause is still unknown.


Cancer is a global health problem that has kept scientists chasing down a cure for a long time. In the absence of a definitive cure in many cases, different methods are used to remove or fight cancer cells. Some popular methods include surgical removal, chemotherapy, radiotherapy (the use of radiation to kill cancer cells) and immunotherapy (where immune cells are used to fight cancer cells).


In cancer treatment, chemotherapy is the use of medications (or a combination of medications) to stop or slow down the growth of cancer cells.


How does chemotherapy work?

One characteristic of cancer cells is that they actively divide rapidly to produce more cancer cells. Their nuclei (the part of a cell that contains genetic material) actively directs and coordinates this division process.


Chemotherapy drugs disrupt this cell division, killing these fast-growing cancer cells. Once a person receives chemotherapy, the drugs spread throughout the body through the blood, killing cancer cells wherever they are located.


Because of this effect, chemotherapy can be used to shrink a cancerous tumour, induce remission, improve symptoms. Depending on the type of cancer, chemotherapy can also be used in combination with other methods like surgery and or radiotherapy to effectively treat cancer.


For example, chemotherapy might be administered to a patient who’s being managed for . It can be given before the surgery to shrink the tumour, making it an easier job for the surgeon or increase the surgery’s chances of success. It can also be given after the surgery decrease the chance of cancer spread or recurrence.


How does it cause diarrhoea?

Here’s one thing that causes most common side effects of chemotherapy: the medications inability to distinguish between rapidly dividing cancer cells and the body’s rapidly dividing normal cells.


Examples of cells that divide rapidly in the body are:


While chemotherapy is effective in killing and stopping the growth of cancer cells, they can also affect these normal cells, leading to .


When it affects the cells in hair follicles, chemotherapy patients lose their hair. When it affects the blood cells in the bone marrow, it can lead to a decreased number of circulating red blood cells, white blood cells and platelets. This is why some cancer patients on chemotherapy may have anaemia, a weaker immune system and an increased tendency to bleed into their gums or poop.


When it affects the fast-dividing cells of the digestive system, chemotherapy can cause diarrhoea.

The damage to these cells affects the absorption of water from the digestive system back into the body.


Diarrhoea is when a person passes more than three stools in a day. It is usually loose, watery and could contain mucus.


Sometimes, can also lead to the passage of green stools (instead of brown).


When the chemotherapy sessions are over, the fast growing cells are no longer under threat from the medications, so hair grows back, and diarrhoeal episodes are less frequent

What can be done about diarrhoea in patients undergoing chemotherapy?

If ignored and not managed properly, diarrhoea can be life-threatening. The continuous loss of fluid can lead to dehydration, a low blood pressure, shock and death.


Here are ways diarrhoea is prevented and treated during chemotherapy:

Dietary modification

When undergoing chemotherapy, patients are usually advised to avoid foods that can irritate the digestive system like spicy, greasy, fatty and fried foods. Alcohol and caffeine intake should also be avoided.

Patients can take meals that are easy to digest, like rice, bananas, toast, white bread and scrambled eggs.


Drinking enough fluids

When it comes to diarrhoea, hydration is key. Dehydration is one important reason why diarrhoea can be deadly. It is advised that patients on chemotherapy take in sufficient clear fluids every day. This helps to replace the fluid lost from the frequent loose and watery stools.


The use of medications.

Some over-the-counter drugs like loperamide can be taken to slow down bowel movement and decrease diarrhoeal episodes.


While chemotherapy is very useful in killing and stopping the spread of cancer cells, it doesn’t come without side effects.


Chemotherapy affects rapidly dividing cells including cells of the skin, hair, blood and digestive system with diarrhoea being one of its side effects.

Dietary modification, sufficient fluid intake and the use of medications can decrease the effect of chemotherapy on the digestive system.


It is also very important for patients to discuss with their doctors about the possible side-effects of any drugs before taking them.


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Dr Omiete Charles-Davies is a medical doctor and founder of 25 Doctors, an online platform where you can ask doctor medical questions online.

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