Jason Isaacs had a "decades-long love affair with drugs".
The 57-year-old actor has an "addictive personality" and by the age of 16, he'd already been abusing alcohol and turned his attention to illegal substances, and refused to listen to pleas to stop for almost 20 years.
He said: "I was convinced no one came from the same twisted, dark, cracked mould as I did, so advice from anybody else was coming from normal people from the normal world.
"What could they possibly understand about me and the noise in my head? I was terminally unique.
"I've always had an addictive personality and by the age of 16 I'd already passed though drink and was getting started on a decades-long love affair with drugs. Every action was filtered through a burning need I had for being as far from a conscious, thinking, feeling person as possible.
"No message would get through for nearly 20 years."
The 'Harry Potter' actor - who has two daughters with wife Emma - was just 12 years old when he got drunk for the first time at a wedding, and despite getting injured when he fell, the incident wasn't enough to put him off alcohol.
He told Big Issue magazine: "The barman, who we thought at the time was a hero and I now realize belonged in prison, sneaked us a full bottle of Southern Comfort.
"We drank the entire thing in the toilet, then staggered out into the party, reeling around farcically. I vomited, fell on and pulled down a giant curtain, snogged a girl, god bless her... ran out into the street, vomited again, tripped, smashed my head open on the pavement and gushed blood all over my clothes.
"The next morning, I woke up with a splitting headache, stinking of puke with a huge scab and the memory of having utterly shamed myself.
"All I could think was... I cannot f****** wait to do that again. Why? I've no idea. Genes? Nurture? Star sign?"
"I just know I chased the sheer ecstatic joy I felt that night for another 20 years with increasingly dire consequences."
The 'Star Trek: Discovery' actor thought he was "broken" while in the grip of addiction and reached a point where he "probably wouldn't mind" if everyone he knew died.
He said: "I remember there being a moment, not long before I got clean, when it suddenly occurred to me that if everybody I knew died, literally every single person, I probably wouldn't mind that much.
"In fact, I might like it, because then it would be an excuse to sit in a room by myself and take drugs and everybody else would say, 'Well you know, fair enough, you heard what happened didn't you?' "
But he later realized that "that's not true and never was".
He added: "I love, I feel, I connect, I care. We all do. The drugs weren't a way of dealing with that sense of distance, the drugs were causing it."