Not only is it not proven for <insert drug here>, it's not even a useful hypothesis in the scientific sense. No one has ever proposed a useful model of the "chemical balance" that is hypothesized to be "imbalanced", so the whole theory is a non-sequitur. It is proposed because the more accurate explanation of "this is a powerful drug that introduces long-term changes to the structure of your brain. A few cherry-picked studies funded by pharmaceutical companies seem to show that there might be some short term amelioration of your symptoms. We have no idea how it works, but that's not surprising, as we have no idea why you have your disorder, or what it is other than a particular constellation of symptoms. We won't find out in the near future, because there's really no money being invested in finding out the ultimate causes for mental illness or in studying the long term effects of these treatments." doesn't get you invited to the really nice pharma-sponsored conferences.