I wonder if depression and depressive episodes could have the purpose of preventing natural tolerance to pleasure chemicals? The brain senses that it's getting a little too much, and reels it in for a little while, resulting in a short-term depression that prevents long-term issue.

But we're so bombarded by stimulants these days that these episodes have to become more severe and more frequent, and the system falls apart.

What do you guys think? Is there any research to support or deny this?