You have to be a little careful with such medication purely bacause you're drinking a lot of water and sometimes, if a person drinks too much they may flush the drug out of the system before it's had the chance to do it's business. For example, someone with bi-polar disorder and on Lithium would be advised against this diet for the very reason that it affects them severly if their drug is diluted.
With anti-depressants, depending on your dosage and the relative psychological state, I don't think it will make such a drastic difference. Just be a little bit more careful not to drown yourself with liquid and take it in an even and steady manner throughout the day.