My program advised no caffeine for at least the first 6 months after surgery. But I missed it too much, and drank a cup of coffee about 10 days after my RNY (12/12/19). I suffered no negative effects at all from it. At my 2-week post-surgery appointment, I told the dietician that, and she said, yeah, we recommend no caffeine for 6 months because SOME people can't tolerate it until their system is completely healed and stabilized in their "new normal." But she said some people are OK right off the bat, and if I was one of those, go ahead and have caffeine. So I have been drinking caffeine for about 4 weeks now, no problem -- 1-2 cups of coffee each day, and at least 1 20 oz diet soda a day, too.