Whitney Purvis is in police custody after being arrested for felony involuntary manslaughter involving a fatal overdose … TMZ has learned.

The “16 and Pregnant” star was busted Monday by sheriff’s deputies in Floyd County, GA … according to online records. The involuntary manslaughter charge is for intentionally distributing a drug called Tranq — a combo of Fentanyl and Xylazine.

Cops say the Tranq caused the victim — John Mark Harris — to suffer a toxic overdose.

Whitney’s arrest for Harris’ death comes a little over a month after her teenage son, Weston, died of natural causes.

In addition to involuntary manslaughter, she was also arrested on 2 other charges involving controlled substances … including possession with intent to distribute.

The former teen mom has been arrested three times before … but for much less serious allegations. She got busted for allegedly shoplifting a pregnancy test, smashing up some electronics and failing to pay child support.

We reached out to Whitney’s camp … so far, no word back.