Chronic sinus infctions. They started out occuring every so often, nothing to be alarmed about yet right before I stopped taking singulair I was in at the doctors at least every 4 weeks for sinus infections. I was on antibiotics for almost one month before I stopped taking it and it was a factor in my coming down with bronchitis. I have stopped taking the drug when I realized it was making me sick. It's been 8th months and I have been to the doctors for a regualr check up and one infection. It feels great to have figured out why I was so sick. I had undergone CAT scans and saw an ENT and I was about to undergo more tests and see another specialists. I have researched online about possible side effects and infamed sinuses and respiratory infections are listed as side effects. The ironic part was I was taking singulair to prevent the sinus infections which my doctor and I thought were caused by my severe allergies when in reality it was actually making me sick. I cannot describe how much I loath this drug and feel that Merck does not do a proper and good job in making all the possible side effects know. My life health wise was...I don't know how to describe it- I was constantly sick and missing school and work and feeling terrible- I guess the word would be terrible. I strongly reccomend a person who is new to taking this drug to research it and know all of the nasty side effects.