Kefir is a source of beneficial bacteria for your gut, not a treatment for depression.
Depression comes from the gut , i know that pretty well .... bad bacteria/yeast can influence how you think,feel,behave via the "Vagus nerve" . This nerve comes from gut through spinal cord , throat,ear ...and brain.Bacteria communite with the gut receptors , however this indirectly stimulate your behaviour.
Cut sugar,alcohol and all that crap . Focus on fermented foods , add high quality probiotics , prebiotics (FOS,GOS,Inulin etc.) to build powerful friendly colonies .
And i can guarantee you that you will feel sense of well being 24/7 .
"A men is what his microbe makes him "
I recently read an article that says priobiotics help with depression. Reuteri is right. I think you should give it try, and see if it helps. No harm done from a drink.