Bob, I have used Singulair to treat asthma resulting from 10 years of using the beta blocker Inderal. It is to be taken in the evening, that's what the leaflet, pharmacist and doctor instruct. Initially, I got massive sudden onset headaches, about one after taking the dose. They were nasty, but after a week they stopped occurring. Also, for the first week I woke up during the night and again in the morning with vertigo (which I am prone to anyway). Again, that only lasted a week. My tongue felt kinda weird for a while, too. This medication helped my breathing immensely. I am only on this med for a short term so don't know anything about long term effects, but I'd be careful. The FDA seems to be allowing an awful lot of new drugs on the market without checking them out fully. I don't like to take anything that hasn't been used for at least 2 years, I'm letting everyone be my guinea pigs. Best of luck.