I have used Castor Oil to induce labor twice. The first time I used it I was only a couple of days before my due date, and my doctor was going to induce me. I was scared of the induction, so I drank the Castor Oil. I mixed a whole bottle in a glass of orange juice. It was totally disgusting, but it worked. I spent hours on the toilet, and didn't get much sleep that night (I drank it around 7 pm). By 8:00 the next morning, my water had broke. When my baby was born, he'd had a bm inside me. But he didn't breathe any of it in, so he turned out just fine.
The second time I used it was this past October. My doctor said I was having a big baby, so he told me that if I hadn't gone into labor by 39 weeks, he was going to induce me. I still was afraid of the induction, so I drank the oil again. This time I drank the whole bottle really fast and did not mix it in anything. It was still gross, but not as bad as mixing it in juice. I did it in the evening again, and was up and down all night on the toilet. By 5 am I was in labor with contractions coming every 2-3 minutes and had a bloody show. My baby was delivered at 39 weeks, and my doctor was right. He was huge--10 pounds 10 ounces! The baby did not have a bm inside of me this time.
So it is up to you. You will have to decide if the good outweighs the bad. If you are truly miserable (I was with my second pregnancy--I hurt so bad I could hardly walk and couldn't hardly lay down without being in pain) and close to your due date by a week or days, then I don't see what it could hurt. If your body isn't ready, then you won't go into labor. The cramping and diarrhea wasn't that bad for me. Labor pain hurt more than the diarrhea cramps.