I suffer from depression. Long term life-long depression. Kava has both helped and hurt with depression. My depression is anxiety-fueled. That is, anxious worrying leads to self-reinforcing internal monologue which leads to depression. Kava can stop that first bit, which is great, but it doesn't always give me mood elevation like my anti-depressant does. I take Cymbalta daily, and it gives me a baseline mood (that still craters from time to time) whereas kava doesn't seem to *set* my mood so much as make my mood more peaceful.
If I'm dragging my ass because I'm feeling low energy and depressed, adding kava doesn't give me a lift. Even heady kava. I eventually stopped drinking it every day because after some time it felt like it was ADDING weight and all the caffeine in the world wouldn't get me to work that day.
So I've had a mixed bag. In terms of quieting the anxious voice that leads to depression, it's done WONDERS for me. As far as mood lifting, I get much better results from exercise (riding my bike, a brisk walk, epic air guitar at a metal show, a trip to the gym) than I do kava.
Sleep helps too, though with depression that can be a double edged sword too. I can tell you that if I get shitty sleep even one night, the next day can be depression hell for me. When I don't get enough rest, everything seems 100x harder and I feel like I'm at the edge of tears and about to lose my shit over the tiniest thing.
Finally, eating good vitamin-rich, protein-rich food can be the difference between escaping the depression gravity well and getting sucked in: all other things being equal.
Kava has proven to be no magic bullet in that area, but it's still pretty magical in every other way.