The Action News investigative team warned about the drug's danger in 2024, when it popped up in Philadelphia.
RELATED: FDA warns consumers about dangers of 'gas station heroin' | Here are the facts
It's often sold in bottles, which can also be found in vape shops.
Despite being highly addictive, the opioid-like substance is not illegal in Pennsylvania, New Jersey and Delaware.
Tianeptine has been linked to death, respiratory depression and severe sedation when misused, according to the FDA.