As a parent of someone with CF (now 26 years old ) I was told to not give him anything to prevent coughs . But he had a bad coughing spell last winter so he requested that we give him something we use . Its called '' Buckley's'' Canadians will know what it is as its made in Canada but distributed here in the U.S. and can be found at a Rite-Aide if you have that pharmacy in your area . They usually don't carry a large supply , so you'll be lucky to find it . Its the only thing thats ever worked for me . 1 tsp. (5 ml ) which is a very small amount , and not recommended for anyone under 12 because its just plain nasty tasting and the say so on the box . You'll find video's on youtube of people taking Buckley's , but it does work .