I'm sure this thread will get all heated but I'm going to post my experience with castor oil (I've copied it from a previous thread about it). I honestly don't think it's as bad as many want to claim and studies have been made that show there is no proof it causes distress, makes the baby poo...etc. But as with anything, read and gather info and make your own opinion.
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I tried using it (a couple times actually) during my first pregnancy. It never worked and never helped me go in to labor.
It did however, cause me to throw up, have diarrhea (almost instantly) and have a ton of contractions. I tried it when I was somewhere around 36 weeks and again at 38.5 weeks (somewhere around those time frames, I don't remember exactly).
It's nasty to drink on your own. It tastes like Vaseline (petroleum jelly). It was terrible mixed in with Coke (it was a funny story, at a restaurant with friends, they were watching me do it, took a sip and threw up all over the table! Thank goodness I was obviously pregnant and everyone around me rushed to my aid. I obviously didn't tell them I caused myself to throw up by attempting to drink C.O.) and worse mixed in with orange juice (I think that was the suggestion drink on some websites). I was able to drink it with chocolate milk (stirred it up VERY good so it looked like a bunch of oil bubbles on the top). I had a very hard time drinking it still due to the taste but managed to down it by plugging my nose, closing my eyes and drinking quickly. I tried to convince myself I was drinking a Frappachino (frozen drink from Starbucks - same consistency as a milkshake basically).
Yuck. Seriously, it fuc*ed me up. I scarred myself for life and am now unable to drink store made chocolate milk without flashbacks of the nasty Castor oil drink. The thought of Castor oil alone turns my stomach and makes me want to vomit. I actually had to stop writing this post 2 times because I was about to hurl...I've heard using it CAN cause some to go in to labor but I was unsuccessful and 5.5 years later it still affects me psychologically!
So if you DO go this route, find a proper drink to mix it with. Chocolate milk, for me, was the best because the bubbly, oily texture reminded me of a thick milkshake (it doesn't taste good though, remember that!). And stay close to the toilet because within 5 minutes your bottom will be exploding! After all, it IS supposed to be used as a form of laxitive...
With my second, I swung on a swing. Didn't go super high or anything but enough to give gravity a boost. My 2nd daughter was born within 2 days.
With both I also drank a lot of rasberry tea. Definitely can give you contractions/braxton hicks but not always. My dr said it's ok to drink anytime really (within moderation, as with most things) because it helps strengthen a woman's uterus and drinking it too early won't cause pre-term labor or anything. I drink it often now and it'll sometimes give me a BH or two but I remember drinking it late in pregnancy and it giving me a ton of them.
Either way, good luck and be safe.