Juice WRLD's Ex-Girlfriend Claims He Mixed Percocet with Lean

Juice WRLD had a habit of taking up to 3 potent Percocet pills a day and would mix them with lean ... this according to his ex-girlfriend who claims the rapper became physically abusive when he tried to get clean.

Alexia Smith says she was in a relationship with the rapper for nearly a year in 2018 ... and in that time she'd see him pop pills with lean as he struggled with depression, which she says stemmed from previous heartbreaks and the feeling of being misunderstood.

Smith claims Juice also used weed, Xanax, Ecstasy, morphine and coke ... but Percocet and lean were his go-to vices. She says she tried helping WRLD get clean but, during his withdrawals, their arguments turned violent. In one instance, she claims Juice picked her off the ground and slammed her into a wall ... squeezing her so tight she came away bruised all over her arms.

Smith told the Daily Mail she started dating him in early 2018 ... and when he flew her out to L.A. where he was taking meetings with music labels, she noticed the new drug world surrounding him.

She claims that within days of arriving in L.A., someone from a label gave him morphine and cocaine. Smith says WRLD didn't use coke at the time but it wasn't long before he did.

As we first reported ... the feds were on Juice WRLD's tail long before Homeland Security agents searched Juice WRLD's private jet last week when it landed at Chicago's Midway Airport.