Castor oil is sometimes used as a stimulant laxative for use in treating constipation and irregularity, and may be used to clean out the bowels before an exam or surgical procedure, according to WebMD. The way castor oil works is by increasing movement of the intestines, which allows the stool to be expelled.
As a laxative, castor oil dosage is generally based on age and the patient's medical condition. It is taken by mouth on an empty stomach and may be taken with juice to make it more palatable. Following consumption of castor oil, a bowel movement is usually passed with 6 to 12 hours, according to WebMD.