Campbell is a regular at Narcotics Anonymous and sued the Daily Mirror earlier this year after it pictured her leaving a meeting.
The 32-year-old was awarded £3,500 damages in the High Court over the Mirror's publication of details about her therapy sessions.
But in an interview with Vogue, she said: "It's just about getting through today. I don't know about tomorrow. I can't promise that I won't touch drugs again."
Campbell explained how drug addiction had affected her: "Everybody is different. Some people can do drugs and they're fine. I can't. It affects me in a really negative way and upsets things in my life."
She added: "I enjoyed going to rehab. I met great people. I learnt about more than just my habit, my addiction. I learnt about the reasons behind it."
She says the court battle against the Mirror had left her in the depths of depression.
"I was confident when I was on the stand, but it was after the case that I got depressed," she claimed.
"I didn't want to go out and people didn't understand. They said 'But you won', but I just felt I couldn't hold my head up."
The supermodel, who currently lives in Los Angeles, claimed she is now being boycotted by the British press and is too nervous to spend any time in London.
