I was prescribed Singulair to help control my asthma. I took 10mg for three days, but it made me incredibly tired. It was hard to get up in the morning and I was randomly falling asleep on my desk at work. I began taking half a pill (5mg) and intitially this was better. I was still tired in the mornings, but by noon it had worn off. However, over the next week additional side effects began to arise and increase in intensity. I could deal with the fever, headache, etc., but the mood swings were horrible. I couldn't stop snapping at people. When I broke out in hives, I knew the Singulair had to go. I have been off of it for two days now and am feeling better. The hives are fading and my mood isn't quite so gloomy. I expect I will return to my normal self by the end of this week.
Incidentally, Singulair did work fantastically well for my asthma. My peak flow average went up forty points and overall the readings were greatly stabilized with only small fluctuations. Unfortunately, the side effects just aren't worth it.