The majority of the authorities are of the opinion that all Scottish and Irish whisky is fine. Some people are careful not to drink whisky that has been aged in casks that have previously been used for non-Kosher wine but there are enough opinions who rule that that, too, is not a problem and can be drunk. Whiskey and bourbon made in America is a more complicated subject as they sometimes have non-Kosher ingredients in them and therefore should only be drunk when they have some kind of supervision.
