I come from a family which has depression going back generations on one side. The depression expresses itself pretty much in the same manner from one generation to the next. My great grandfather committed suicide. None of his descendents went that far but most engaged in substance abuse probably to self treat for depression.
The advent of SSRI's has been a godsend for me and my siblings. We are the first generation to be free of what very much seems to be an inherited disorder. I now use SSRI's in very small doses - on the order of 10% of the average recommended dose, and I use other substances and strategies alongside.
"Happiness" is one of those words that means so many different things to different people that it almost means nothing. "Anhedonia" is a word I like to use, because it cuts more directly to the chase - pleasure, taking pleasure.
For people for whom the modern pharnaceuticals work the most noticeable improvement seems to be in the ability to take pleasure - to savor.