This article is from the ER FAQ, by Rose Cooper firstname.lastname@example.org with numerous contributions by others.
In the show`s pilot episode, "24 Hours", Carol attempted
suicide by swallowing a bottle of pills.
Originally, the writers had planned to kill Carol off at that
point, but test audiences liked the character too much, so she made a
recovery in the second episode.
Since it happened before the first episode took place, the
impetus for Carol`s suicide isn`t very well documented, but we do
know that it partially resulted from a recent, badly-ended
relationship with Doug Ross, and stemmed from other factors as well.