Guaifenesin - Is it useful for post nasal drip?

Yes, it can be useful by thinning out the mucus to prevent blockages in the ears and sinuses. Drinking a lot of water is also highly recommended. Antihistamines and decongestants can be useful, as well. The older over the counter versions, such as Benadryl, may not be the best choices for post nasal drip, because when they dry out mucus, they can actually thicken it.(Plus Benadryl makes you very sleepy) Clarainex and Allegra are two good options. I use a saline nasal rinse daily. You can find these at any drugstore. I have had post nasal drip most of my life. There have been times that the mucus has gotten so thick that I have ended up with ear infections and sinus infections. I finally went to an ear, nose and throat specialist who suggested that I use the saline rinse everyday. I have not had a sinus infection since. Best of luck to you!

Not much. It thins out mucous so that it can drain. You need something that will dry you up.