"I can't speak to addiction, but a lot of people would say that if you're using anything as an escape, you have a problem," Agassi, 39, told the magazine.
Agassi's memoir, Open, hits shelves Nov. 9 and covers everything from his failed marriage to Brooke Shields to his drug past.
"I was worried for a moment, but not for long," Agassi tells People about revealing his drug use. "I wore my heart on my sleeve and my emotions were always written on my face. I was actually excited about telling the world the whole story."