Unhappiness: not merely something to be treated
As we now come full circle, for humans it is these feeling and emotions, along with reason and consciousness, which drive humans to pursue the highest possible status, largely via wealth acquisition in the modern age. For great wealth and status are central to maximizing economic, combat, and reproductive performance for individuals and their families. This explains why all human emotions and feelings, except surprise and excitement, comprise what is known as hedonic tone. And even these two exceptions serve to amplify the effects of the emotions and feelings comprising hedonic tone.
That is, all other emotions and feelings operate along a continuum with extreme reward, or positive feelings, on one end, and extreme punishment, or negative feelings, on the other. These have been naturally selected for in accordance with the behaviors that have tended to range from highly beneficial to highly detrimental for human bloodlines through the eons. And it is in this light that feelings that range from extreme happiness to extreme unhappiness provide overall guidance for how individuals are doing with respect to perpetuating their lines.
Hence, as money has become central to achieving the high status that is in turn central to all things positively associated with bloodline survivability, which generally coincide with happiness; one can confidently expect there to be a strong correlation between having money and having happiness, such that the former can be said to be able to buy the latter. And on the flip side, this would mean that those who are unhappy should probably not be seeking one or another new-age antidepressant to feel more happy; they should instead be figuring out what a heritage defined by natural selection is telling them they are doing wrong–wrong enough that they will ultimately become part of the fossil record if corrections in behavior are not made.