Montelukast
"Within days of starting this medication I became a different person.  Anxious, depressed, hopeless.  I thought the world had turned against me for some reason and couldn't muster the strength to get dressed in the morning.  But the worst part, if you can imagine something worse than constant anxiety, was the fear.  It was like being afraid for your life every minute.  I began checking the door locks 5 or 6 times because I feared being murdered in my sleep.  It was when I was making plans to set up my bed in the closet did I finally have the moment of clarity that this wasn't rational thinking and something was very wrong!  Stopped taking Singular and was back to cheerful, sunny, optimistic, confident self in 2 days.  Never again!!!"