The comedian said that losing his friend in July 2011 to alcohol poisoning "had a powerful impact" and inspired him to try "to salvage unwilling victims from the mayhem" of addiction.
"Her death had a powerful impact on me, I suppose, because it was such an obvious shock, like watching someone for hours through a telescope advance towards you, fist extended with the intention of punching you in the face," he wrote in The Sun. "Even though I saw it coming it still hurt when it eventually hit me.
"What was so painful about Amy's death is that I know there is something I could have done. I could have passed on to her the solution that was freely given to me. Don't pick up a drink or drug, one day at a time.
"Spurred by Amy's death, I've tried to salvage unwilling victims from the mayhem of the internal storm and am always, always, just pulled inside myself."
Brand commented that even though in the ten years he has been clean his "life has immeasurably improved", he cannot understate "the efficiency of heroin in neutralising pain".
"I look to drugs and booze to fill up a hole in me," he said. "Unchecked, the call of the wild is too strong. I still survey streets for signs of the subterranean escapes that used to provide my sanctuary.
"I still eye the shuffling subclass of junkies and dealers, invisibly gliding between doorways through the gutters. I see that dereliction can survive in opulence - the abundantly wealthy with destitution in their stare."
Brand revealed that he seriously thought about taking heroin relatively recently, when an unknown girl dashed his dream of becoming a father.
"The last time I thought about taking heroin was yesterday," he said. "I had received 'an inconvenient truth' from a beautiful woman.
"It wasn't about climate change - I'm not that ecologically switched on - she told me she was pregnant and it wasn't mine."
The 37-year-old also opened up about his battle with drugs during an appearance on This Morning yesterday (March 5), in which he made host Phillip Schofield gasp after apparently letting slip a swear word.
Brand is tonight hosting the 'Give it Up for Comic Relief' gig, which will help support those affected by drug and alcohol dependency in the UK.
Noel Gallagher, Nicole Scherzinger, Emeli Sandé, Paloma Faith, Kasabian, Jessie J, Rizzle Kicks and Jake Bugg are among the singers confirmed for the show.
Comedians including Jimmy Carr, Noel Fielding, Frankie Boyle and Simon Amstell are also scheduled to make appearances.
'Give it Up for Comic Relief' will air at 10pm on BBC Three.