Lowe also opens up about his own time in rehab and why he "loved it" so much.
It's something Lowe looks back at now as a "huge inspiration" when it came time for him to do the same just a few years later.
In her new memoir, "Inside Out," Moore recalled her hard-partying days before shooting the Joel Schumacher flick. At her peak, she said she was going through an eighth of an ounce of cocaine every two days by herself -- and word got back to the director. Schumacher and producers demanded she go to rehab for 15 days before filming -- and have a counselor with her 24/7 during production.
She'd write that movie changed her life, explaining, "If I hadn't gone to rehab to make that film, I really wonder if I'd still be alive."
Lowe was a guest on "The View" on Monday, where he was asked about how she faced addiction when they were working together.
"She was the first person I ever knew who got sober. She was a huge inspiration to me," said Lowe. "It was the 80s, we were all doing our thing. I just remember thinking, 'Whoa, if that girl can get sober, anybody can.'"
"I've been sober 29 years, so everybody has that person in their life where they go, 'Oh that's a great example,'" he continued. Lowe went to rehab in 1990, following a sex tape scandal that nearly sunk his career.
"I loved rehab. I loved it. Loved it," he said on "The View." "Because I knew I needed answers that I didn’t have. I learned them there. I was always a pleasure to have in class anyway. It was like going to school to learn how to live your life with tools that nobody ever taught me."
One tool: "Never compare your insides to someone else's insides," he revealed. "I spent a lot of time thinking should I be doing this, that person's doing that. And also, it changed my life. I needed experts. It was great, it was fantastic."
In Moore's book, she also shot down speculation she and Rob were ever much of an item back in the day.
"While in his own memoir, Rob suggests that we had some kind of hot-and-heavy romance; I can vaguely recall one ill-advised late night together, but I'm grateful to him for the complimentary descriptions of our youth," she said. "In truth, I liked all my ['St. Elmo's Fire'] costars and remain close to some of them today."
"Inside Out" is available now.