Wiktionary
chill pill
n. An imaginary medicine taken when excessively anxious or upset about a trivial matter.
Wikipedia
Chill Pill
Chill Pill is the fourth album by the band Warrior Soul released in 1993. The album was remastered and re-released with bonus tracks on CD and MP3 in 2009 by Escapi Music. Michael Monroe of Hanoi Rocks fame plays harmonica on the track High Road.
Usage examples of "chill pill".
I told him to take a chill pill or something or I swear he's just going to woof all over somebody.
He took deep breaths, half expecting her to be bouncing along at his side, poking him, telling him to take a chill pill or something.
She stared me straight in the eyes and said, ``Take a chill pill, man.