• Bowel preparation before colonoscopy. Taking a single dose of castor oil is effective for bowel preparation in people undergoing a colonoscopy. However, castor oil might not be as effective as other bowel preparations, such as sodium phosphate or bisacodyl plus magnesium citrate.
• Constipation. Castor oil works as a stimulant laxative for reducing constipation when taken by mouth.
• Dry eyes. Using eye drops containing castor oil might be effective for people with dry eyes.
• Starting childbirth in pregnant women. A single 60 mL dose of castor oil appears to start labor within 24 hours in at least half of women at term pregnancy who try it. There is also some evidence that women at term pregnancy whose "water has broken" are more likely to go into labor and are less likely to need a Cesarean section if they take castor oil.

BY MOUTH:

• For constipation: 15 mL of castor oil is commonly used.
• For cleaning the bowel before surgery or examining the colon (colonoscopy): The dose for adults and children over 12 is 15-60 mL of castor oil given 16 hours before the procedure. For children age 2-11 years, 5-15 mL is typically used. In children younger than 2 years, 1-5 mL is commonly used.
• For starting childbirth: A variety of dosage schedules have been used. Single doses vary from 5-120 mL of castor oil. A one-time dose of 60 mL in fruit juice is commonly used. Other dosing schedules that have been used include 5 mL in peppermint tea every 2 hours, 15 mL three times daily, 30 mL every 2 hours, 30 mL every 6 hours, 30 mL every 3 hours for 3 doses, 60 ml daily, and 60 mL daily for 2 days.