Obama wrote about his teenage drug in his memoir, "Dreams from My Father." His rivals have largely remained silent on the subject.
"Junkie. Pothead. That's where I'd been headed: the final fatal role of the young would-be black man," Obama wrote. Mostly he smoked marijuana and drank alcohol, he wrote, but occasionally he would snort cocaine when he could afford it.
Speaking to Manchester high school students earlier this month, Obama said he was hardly a model student and had experimented with drugs and alcohol.
"You know, I made some bad decisions that I've actually written about. You know, got into drinking. I experimented with drugs," he said. "There was a whole stretch of time that I didn't really apply myself a lot. It wasn't until I got out of high school and went to college that I started realizing, 'Man, I wasted a lot of time."'