The Scottish musician admits he indulged in heavy drug use in a bid to "obliterate" himself and finally tackled his problems five years ago when narcotics started to ruin every aspect of his life.
He tells Britain's Daily Telegraph, "It put my life in chaos and caused me and everybody around me a lot of pain and difficulties. I don't want to get all American about this. It's not for me to tell other people how to live their life. Most people can have a couple of drinks or lines (of cocaine) and they might say the odd stupid thing or make a pass at somebody, but they don't endanger their lives or put themselves in risky and humiliating situations.
"I just know that they are too powerful for me, and they change my personality for the worse. When you're drinking and drugging, you kind of shut yourself down. It wasn't really about having a good time. With me and my friends, were were trying to obliterate ourselves. The band suffered creatively."
Primal Scream's new album, More Light, is the first material Gillespie has recorded completely sober, and he believes the band's psychedelic style of rock is even better than when the band was high on drugs.
He adds, "We are trying to create transcendent, euphoric, ecstatic experiences. That's always going to be part of our aesthetic. We like making druggy-sounding psychedelic music. It's just that since we stopped taking drugs we got better at it."