What is Sodium Phosphate?

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  • Written By: D. Jeffress
  • Edited By: Jenn Walker
  • Last Modified Date: 21 February 2017
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Sodium phosphate is a very potent laxative that is usually prescribed for patients who are scheduled for colonoscopies. Occasionally, the medication may also be given as a treatment for severe constipation or impacted bowels. When several tablets are taken with water, the muscles of the large intestine are stimulated and the bowels are entirely voided. Besides the desired effect of diarrhea, there is very little risk of adverse side effects when sodium phosphate is taken as prescribed by a doctor.

It is important for the large intestine to be clean and empty before a colonoscopy so the physician can easily inspect the tissue lining. Sodium phosphate induces diarrhea by loosening the bowels and stimulating smooth muscle contractions in the colon. Drinking plenty of water and other clear fluids while taking the medication aids in softening fecal material, making it easier to void.

When a patient is scheduled for a colonoscopy, he or she is usually given a bottle of sodium phosphate tablets by a doctor, nurse, or hospital pharmacist. Each tablet contains about 1.5 grams of the active ingredient. On the night before the scheduled exam, an adult patient is typically instructed to take three tablets at once with a large glass of water every 15 minutes for a total of seven doses. The seven-dose routine is repeated in the morning before going in for the exam.


The laxative effects of sodium phosphate appear very quickly after the first dose. A person should be sure to stay near a bathroom for the entire night and following morning. Frequent episodes of diarrhea, sometimes every five or 10 minutes, are common and desirable. Proper fluid intake is essential to prevent dehydration.

Some people experience abdominal pains, stomach cramps, bloating, and nausea when taking sodium phosphate. Allergic reactions are rare, but a person should seek immediate medical help if he or she experiences light-headedness, difficulty breathing, or a spreading skin rash. Sodium phosphate has been linked to potentially serious kidney damage in some patients and clinical trial participants, but the risks of permanent damage are very low.

Patients who use sodium phosphate exactly as instructed by their prescribing doctors usually have no problem voiding their colons. Colonoscopy procedures can be performed much more effectively when the intestines are flushed. People who are given the drug for other reasons, such as chronic constipation, tend to see immediate relief from their symptoms after a single course of treatment.


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