 Another myth? That most homeless people are alcoholics or drug abusers who spend whatever money they get on their habit. Padgett says experts believe that 20 to 40 percent of the homeless have a substance abuse issue. That's still a serious number, but she says it's rarely the sole cause of homelessness. More often, it's a response to being homeless. We don't want to pretend that they don't spend money on drugs or alcohol, but so do the rest of us.