hi. in my limited, personal experience, ssri drugs, ssnri drugs, too much tranquilizer/antipsychotic, and too much mood-stabilizer can lower my mood, sometimes to the point of bona fide depression. oh, and Klonopin...watch out for that bad boy. Long term use can cause or exacerbate depression, more often than other benzodiazepines.

I hope things get better for you.