Sorry pusskin....can't help you.......catarrh is a layman's term and is a symptom of some disorder. Too many disorders to go into, but just a few common ones.
Respiratory infections, bacterial or viral usually goes when the infection goes and if it doesn't it may need medical attention.
Smokers have catarrh....stop smoking.
Working in dust atmospheres may cause the problem.
Moving from a warm atmosphere to a cold one e.g winters in the UK, going from a warm house to the outside.
ANxiety states can cause catarrh.
Allergies can can cause the problem.
Vasomotor rhinits.....medical term which means "We have no idea."
So you see pusskin, I have been of little help.
I am not a great believer in decongestants taken in tablet form, but prefer nasal sprays or douches. Some on the market contain sea water which is supposed to help.
Clanad is an American ABer who is fond of an American product, the name of which I have forgotten, but if he sees this thread he will inform us.