I have had some experience with depression, taking antidepressants, and reading tarot. All of the drugs I tried were in the SSRI category.
As depression set in over the years, my spreads would take me 'round and 'round in circles with a spiraling downward effect. It seemed as if there was no way out and no answers for anything I asked. I felt blind and helpless, and my readings were mirroring those emotions. I stopped using the cards at all at this time. I missed them, however, and NOT drawing cards was one of the catalysts that prodded me into searching for help.
In the search for a medication that would actually help me, I found that Prozac, Paxil, and Zoloft all effected me in the same way: I was no longer a pile of sobbing mush, but that was because I just didn't care about anything. I call it The Zombie Effect. I would sit and stare at the cards (or the dishes, or the dust on the tables) and not be able to focus on what to ask, what to do next, or even to feel the energy from the cards or people like I had before. This was one of the reasons I kept changing medications after a 60-90 day trial of each.
Lexapro finally did the trick for me. After a couple of weeks on this medication, I started to think and feel "normally" again, and I felt in touch with my cards and with people again, at last!
My conclusion from this is: The ability to read tarot is directly connected to how clearly you can see yourself, your ability to focus and make decisions, and how well your mind can process information and energy. The healthier you are mentally and spiritually, the more precise and accurate your readings will be.