Six months probably isn't necessary. In fact, it's definitely not. No antidepressant in existence takes that long to work. If you really want to be careful, you can wait 3 months, but that is plenty long enough. If you make yourself wait for 6 months with every med you might end up trying, it could be years before you feel better.

For example, I was first put on Prozac, then Zoloft, before eventually finding Cymbalta was what worked. That would have been a whole extra year I would have suffered! Now, I am once again having to find something else. So far, I've struck out on 3 antidepressants and am on my fourth. It's only been about a month, so we don't know if it's going to work yet. However, if the second month ends and I don't feel better, I'm going to want to move on. Because I want to feel better and there's no sense in dragging my heels about it.