I think you can be honest with adcoms about it IF you have a good story for how you've done hard work to overcome it and you'll know what to do if it happens again without needing to take time off of school. So being on meds or knowing already what meds work for you, or knowing that exercise and service are key to your emotional stability.
If you DON'T have a handle on it, and you don't know what happened or why or whether it'll happen again or what you'll do and you're just hoping for the best, then (a) think hard about whether that's going to set you up for success in med school and (b) definitely don't bring it up.
That said, it seems to me that every med student gets depressed, at least during residency.