Ritalin can be used for some symptoms of depression--lack of concentration, fatigue, lethargy, etc.--but I don't think its usually used as the only drug for depression, unless you're elderly and/or have physical health problems that make conventional antidepressant drugs a no-go.

Personally, I found that Focalin (a supposedly improved version of Ritalin) and Adderall both lifted my mood, but I still needed conventional drugs. I have a friend who takes a low-ish dose of Lamictal and a low-ish dose of Adderall XR, and that combination seems to help a good bit.

Just do be careful. Even people who don't have mood problems, psychosis, etc. can go full on manic and/or psychotic on stimulants, even at normal doses. Believe me when I say that prescription amphetamine psychosis can sneak up on you, and its not a fun experience.

Having said that, its between you and your doctor. I'd personally just try to keep the dose as low as you can and try to use long acting formulations, if you can.