Rob Lowe Says Getting Sober 34 Years Ago Was an 'Incremental Decision' Culminating in His 'Final Wake-up Call' (Exclusive)

It wasn’t just one thing that led Rob Lowe to quit drinking 34 years ago. As is the case for many recovered alcoholics, Lowe's road to sobriety was a process of self-reflection marked by big and small wake-up calls.

"Getting sober was an incremental decision," he tells PEOPLE in this week's cover story that celebrates 10 transformative moments in the Hollywood icon's life. "It's baby steps until you're ready. You can't do it until you’re really ready."

Before entering rehab at Sierra Tucson in 1990, Lowe, 60, recalls experiencing myriad nudges along the way.

One "baby step" came when he watched Warren Beatty, one of his "heroes," in the 1975 romantic comedy Shampoo. "It’s a great movie, but at the end, he's a bon vivant, charming playboy left with nothing," he says. "It affected me tremendously and [was] the first glimmer of your conscience, your destiny, God, going, 'Psst, pay attention to this.'"

Another meaningful moment came after the now-infamous sex tape of him hooking up with two young women around the 1988 Democratic Convention was leaked to the public. "[The fallout] definitely changed my life at the time, and, in hindsight, I realized it was another step that led me to recovery and reevaluating my life," he says. "But the thing that really changed me was not being able to show up for my family and myself."

That low point came in 1990 when his beloved grandfather had a heart attack, and Lowe ignored his mom's desperate call. 

"I remember like it was yesterday: My mom telling me [on the answering machine] to 'pick up, pick up' because my grandpa had had a heart attack. I couldn't deal with it in the state I was in, and I needed to go to sleep to wake up so I could deal with it," the Unstable star recalls, noting he immediately turned to tequila. 

"Who doesn’t keep a bottle of Cuervo Gold by their bedside table? That was the final wake-up call. I’ve been sober ever since."

By the time he got to rehab, he says he was "so ready" to move past his hard-partying days. "It was relieving, and it was scary, [but] I learned the tools to change your life if you have the self-honesty to do it," he says. "I felt, 'Oh, okay, I'm not alone. I'm not crazy'."

Lowe never looked back. 

"I didn't have any doubts [and] I wasn't like, well, maybe I'll be sober for a little bit," he says. Instead, he just knew he was done. "I always tell people: you can't get sober... I don't care if it's fentanyl, booze, drugs, coke, pot, gambling, overeating, sex addiction, whatever, you cannot stop for your job, your wife, your family, your parole officer, because you screwed something up."

At the end of the day, Lowe says, "You only are going to stop when you're ready, period."

For more from Rob Lowe's exclusive PEOPLE cover interview, please pick up this week's issue, on stands Friday.