asthma
"This review will not completely apply to most people as I am bipolar II and am extremely sensitive to some kinds of medicines. 
It normally takes me a very long time to fall asleep (sometimes until dawn) but once I am I stay asleep and get plenty of rest. On Singulair I once couldn't fall asleep until about 12:00 in the afternoon after going to bed at 11:00 pm the night before, and I would often wake up multiple times while sleeping. My anxiety was much higher, I was significantly more depressed, and my previously very well stabilized mood was once again destabilized. I also had some water retention weight gain. Was absolutely amazing for my asthma though, so I guess that's something. Really wish it played nice with my sleep and bipolar."