"I got caught up in my new lifestyle and got carried away with drugs and alcohol," says Jack Osbourne, 17, telling PEOPLE exclusively about why he checked into Las Encinas, a Pasadena, Calif., psychiatric and chemical-dependency hospital on April 23.

On his fourth day of treatment there, the youngest member of heavy metal's first family told the magazine that once he realized his predicament, "I voluntarily checked myself into a detox facility for my own health and well-being."

Ozzy, 54, whose own struggles with drug and alcohol addiction are well documented, had long worried about history repeating itself. Segments of MTV's "The Osbournes" have shown him lecturing on the evils of drug use to children Jack and Kelly, 18. (Aimee, 19, does not participate in the show.)

The lectures paid off for Jack, who took a break from partying in February after admitting to mom Sharon (then finishing up her chemotherapy treatments for colon cancer) that he was overindulging in marijuana and alcohol.

But he reportedly fell into old habits during a recent stay at his parents' Malibu beachfront home and was encouraged by his folks to change directions.

"It takes a lot of courage and strength to admit you need help," Ozzy tells PEOPLE, "and both Sharon and I are proud Jack is facing his problems head-on."