EXCLUSIVE

Lex McAllister, a contestant on one of the most popular seasons of "The Bachelor" is dead, and authorities and her family believes it's a suicide ... TMZ has learned.

Lex appeared on season 14 of the show with Jake Pavelka ... she was eliminated after the first week. Lex made waves when she spoke out about Jake's breakup with Vienna Girardi (the season's winner), saying Girardi was not at fault.

Law enforcement sources in Columbus, Ohio tell us they received a 911 call Saturday at around 2 PM ... the caller stated Lex had texted her earlier that day saying she wanted to "end her life" and when the caller went to check on her it appeared Lex had OD'd on prescription pills.

She was taken to a hospital in stable condition but, according to her family, her body started to shut down. The family withdrew life support and Lex died Tuesday morning.

A member of Lex's family tells us, she struggled with depression and bipolar disorder.

Gia Allemand, who was also a contestant on Lex's season of the show, committed suicide in 2013 by hanging.