During an interview with radio host Howard Stern that aired Monday on SiriusXM, the actor opened up about several aspects of his personal life, including his stint in rehab, the death of his mother and the huge bombshell that he got a woman pregnant in his late 20s.
"I really don't have anything to hide anymore," said Stamos, who clarified that he now doesn't drink and also doesn't miss getting high "at all."
"My father passed away and I got divorced ... it sent me sort of down a wrong path," he said, adding that his mother's passing in September 2014 "knocked [him] off" and was "very hard."
Stamos explained that throughout his life, he had always been able to stop drinking when he needed to for work, but things came to a head this summer after he was arrested for driving under the influence and sentenced to three years of probation for the charge.
"I could stop [drinking] on a dime. I could stop. In the times that I went back, it just sort of deteriorated my life, and who I was, and my morals and my values. I lost myself, I lost my sense of discipline, which my dad taught me so well, and I just became someone – more and more I was just dipping into that dark place. It happened more and more and it just got darker and darker," Stamos said. "It stunted my growth. Emotionally – maybe I would be married with kids right now."
"I had a horrific DUI, which I am so embarrassed by," he continued. "I could have hurt somebody, it was really stupid and ignorant of me. And I hated myself for that. It was a bad, bad thing. So I said to myself, I have to stop this up and down, up and down, I have to."
Stamos entered a 30-day substance abuse program in July.
"I walked in those doors, I said, 'Tell me what to do,' " he said. "I'll do anything I can – and if it doesn't work after the time, then it didn't work, but I'm going to apply myself a hundred percent to it. Which I haven't over the years."
Of what might have caused his issues, Stamos said he was "hurt from losing my mom."
"I derailed over the years. I never really got back on track," he explained. "A piece of me just was gone. ... It was a big part of my purpose for many, many years to be there for her and be a good son."
The Grandfathered star also revealed he was taking Ambien to help him sleep at night, but that the medication affected his ability to work.
"I was on some medications, antidepressants and that damn Ambien, I'm so happy to be off that. Completely off. I don't take anything," he said. "My memory was starting to get really f---ed up too, from that. Difficult to memorize scripts, I couldn't remember names and places and things. And that was the hardest thing to kick, by the way. Booze, and whatever, that happened, but the Ambien was tough."
In addition to the difficult past couple of years, Stamos also opened up about his youth and the women in his life.
When Stern asked Stamos if, given his success with the ladies, he'd ever gotten someone pregnant, the Fuller House star revealed he indeed conceived a child in his late 20s, but the woman got an abortion.
"This was just bad timing. It really wasn't my choice … I think it was sort of a mutual decision," he admitted.
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Now, however, Stamos insists he is in a much better place in his life.
"Those days are over. I feel even all the time," he said.
Fuller House will stream on Netflix on Feb. 26, and Grandfathered airs Tuesdays (8:30 p.m. ET) on Fox.