I wouldn't recommend doing this these days, but when I was 3 weeks overdue with my daughter, my mother told me if I drank castor oil, it would send me into labor. So ... I drank 4 ounces of it. Oh man! I had the runs SO bad (well, what did I expect?) but within 6 hours I was in full blown labor. This was back in the days when they still gave you an enema and shaved you when you showed up at the hospital. I told them I was all set with the enema part!