"Did we ever know why Jackie became an addict?"<br /><br />Jackie ecplicitly states the REAL reason in season 4 to Charlie, arguably the strongest season. For 2 years, her new daughter Grace just wouldn't stop crying. <br /><br />That's why she becomes so concerned about being a proper mother in the 4th season; because admitting that Grace was her "ground zero" as Charlie puts it is almost like giving your firstborn a big F u.<br /><br />Sorry I can't qoute original poster and elaborate more on this dying cell but watch that and some following season 4 eps; they're pretty powerful.
