How do you not puke when robotripping?

So ive robotripped and done skittles thousands of times, but a little over half the time i puke and then start tripping after...the trip is always awesome but im not a big fan of puking, as you could imagine im sure. I know that products with guafesin in them make you puke when you take to much, but i was curious if there were any other tricks to keep from getting sick?