I'm not sure 2C-D potentiates drugs in a physiological sense. Moreso, it seems to create a kind of amplifier to increase the perceived effects of other psychedelics. Obviously, 2C-D is already quite trippy, but adding something like smoked DMT adds up to an increased intensity and longevity. The experience is more intense due to the synergistic effects of two potent hallucinogens, and the length of the experience is only increased perceptually as the 2C-D amplifies the tail end of a DMT trip. If you know anything about audio, think compressors.
And yes, 2C-D is safe for people on SSRI's.