If you need cough syrup to feel better, I doubt whatever sugar is in it is really an issue, although if you use something like NyQuil, the alcohol may be. I have tried both alcohol (1 beer) and carbonated soda (diet) since my surgery and have been able to tolerate all except Dr. Pepper Ten, which came back out like a volcano. I don't have any intention of being a regular user of either, but a Sprite Zero or Diet 7-Up would probably hit the spot for an upset stomach. But I think each of us has our own set of tolerances we have to feel our way through as we go through the post op journey, so what one person can tolerate doesn't mean another one can. Good luck to you with your surgery.