I have depression, clinically treated with SSRIs. My exercise regimen now is 8-10 hours a week of swimming, cycling, and running. I find that the exercise helps lift my mood a lot, but also if I lose my ability to exercise it is far less catastropic to my mental health than if I stop taking the SSRIs.

My exercise volume varies throughout the year because of physical health concerns (sickness, injury, combination of the two), and I notice it and will become mopey, but it's far from the crippling anxiety and depression that sets in if I miss my SSRIs for a few days.

But this is just anecdata, treat accordingly.