Original source: asked doctor for modafinil to enable working harder for more hours. Doctor said, No, you might think it's a good idea now, but if you're back here a couple months later with depression, you'll realize it's not worth the risk.

Looking up some primary source just now: http://www.oncologypractice.com/fileadmin/content_pdf/cpn/ar...

(for some reason the UI doesn't let me reply to the reply, so here goes)

Now that I'm looking around at papers, it seems like there is evidence that it helps patients who are already depressed get some energy back.