'16 & Pregnant' Star Whitney Purvis on Suicide Watch in Jail Following Arrest

Whitney Purvis has been placed on suicide watch at the Georgia jail where she's being held for involuntary manslaughter ... TMZ has learned.

Law enforcement sources tell us the "16 and Pregnant" star was medically designated and committed within the jail system after making suicidal comments behind bars. Our sources say she's also undergoing a detox as she withdraws from drug use.

We broke the story ... Purvis was arrested Monday, accused of distributing a dangerous street drug known as "Tranq" -- a lethal mix of fentanyl and xylazine.

Authorities allege the drug led to the fatal overdose of John Mark Harris earlier this year.

An investigation by the DEA remains ongoing. On Monday, the DEA said the case is part of a broader crackdown on fentanyl-related deaths ... noting nearly 70% of all drug fatalities in the U.S. currently involve synthetic opioids like fentanyl.

We've reached out to the Floyd County Sheriff's Office, who declined to comment.