The rocker mixed pills for insomnia and anxiety with shots and beer and suffered a meltdown during a gig in Las Vegas in September (12), but he admits that wasn't the first time he was "loaded" onstage.
Now in recovery after a rehab stint, Armstrong tells Rolling Stone magazine, "I played onstage loaded a lot. I'd have anywhere from two to six beers and a couple of shots before I went onstage, then go and play the gig and drink for the rest of the evening on the bus.
"(I'd) fall asleep, wake up the next day, feel like s**t, do soundcheck... It was over and over again. In that way, I was a functioning alcoholic.
"There are a lot of gigs where I definitely walk that line between what is control and what isn't. I like the feeling, like you're walking on air."
And he admits his heavy drinking spiralled out of control in the weeks before his meltdown as he attempted to cope with pre-gig nerves before a big show in New York and the anniversary of his father's death.
He adds, "It was the New York jitters. I threw back four or five beers before we went on and probably had four or five beers when we played.
"Then I drank my body weight in alcohol after that. I ended up hungover on the West Side Highway, laying in a little park.
"That show (in New York) was also the 30th anniversary of my father's death. That was weighing on me... It was a pretty heavy night."