In a cage, rats would consume drugs until they starved.
In a happy, healthy environment, rats would avoid the drugs and addicted rats transferred from the cages would stop using drugs.
Well we all know our street people are perfectly happy in their lives which feels nothing like a cage to them.
That being said, the street people I knew would generally go on three day binges, after which they would collapse into a near comatose state and sleep for a day or so, after which they would eat everything they could get their hands on.
During the binge? They didn't eat much. They were all, without exception, quite skinny. Skeletal in fact. (This is one of the milder pictures available.)
No, I assure you there are many people in our society that feel like rats in a cage. The fact that they have all these other distractions does not relieve them of this feeling.