Never had sleeping problems after drinking Mekhong-cokes and I had plenty of them on my last visit.
As red bull is a pep-drink it seems more likely they mess around with it. I am sure it's not only the huge quantities of sugar, which keeps you awake. But having said this; I don't think the Red Bull company would allow it, that they add speed to their product. Think the drink would be forbidden in no-time if this would come out.