Since coke is acidic anyway (phosphoric acid) it shouldn't be neutralised, but remember that even tap water can break down LSD over time, so you may want to test it.
I certainly hope you're not dosing someone without preparation. I don't think explicit consent is completely necessary, but if someone's not ready it could be a hellish experience that they will resent forever and probably never forgive you for.
/end of moralistic rant