Apparently drinking castor oil and OJ makes your intestines overwork, which can bring on contractions, these will only be labour ctx if your body is ready.
However as PAL said it can cause issues, like awful d&v and dehydration, it also won't work unless your body is starting to get ready for labour anyway.
A lot of MW's still reccommend it but there have been horror stories of people using it, and basically people self-medicating, taking way too much, becoming ill and not being able to cope with the labour, so if anyone is considering using it I'd say it has to be a last ditch attempt, has to be done properly and should be done as close to the end of pg as possible, being overdue and using it can cause baby to poo in the womb and have meconium in the waters, using too early can cause you to be quite poorly.
I wouldn't reccommend it for most of the mothers on this thread personally tbh, especially not first timers, there are many other ways to get baby out and unless waiting is a real issue then wait you should.