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The use of castor oil to induce labor is controversial. One study showed that women who receive castor oil have an increased likelihood of initiation of labor within 24 hours compared to women who receive no treatment( Following administration of castor oil, 30 of 52 women (57.7%) began active labor compared to 2 of 48 (4.2%) receiving no treatment).[32] However, another study showed that castor oil had no effect on the time to birth in women whose pregnancy exceeds 40 weeks.[33]
Castor oil, when ingested, triggers cramping in the bowel, making it an effective laxative. Thus, it is intended that such cramping extend to the uterus. In an overdue pregnancy in which the mother's cervix is already effacing and partially dilated, this cramping can lead to labor contractions.[citation needed] The irregular, painful contractions of castor oil-induced labor can be stressful on the mother and fetus.[citation needed] It also leaves the laboring woman quite dehydrated as a result of the vomiting and diarrhea which result when the recommended dose of castor oil for labor induction is taken—2 oz, or about 4 tbsp.[citation needed] This leaves her without access to the energy she could otherwise derive from food or drink throughout her labor process. Using castor oil for induction is not recommended without consulting a medical practitioner and is not recommended in a complex pregnancy.