If you are taking antidepressants, most of which have a chemical structure very similar to psilocybin, you will have built up a strong tolerance and it will be very difficult to trip. Moreover, the way these chemicals interact in your system is unpredictible. If you megadose in order to inspire a trip, you stand a very good chance of having a bad experience.
My opinion of antidepressants is not very favorable. I took them for years before I learned of the many dangers they present. Moreover, withdrawal from most of them is a difficult process. It needs to be done slowly over a long period of time, or it can provoke some very nasty reactions. Initially, when you start to withdraw, you will experience some ugly moods and other things that will serve to confirm in your mind that you "need" the drugs. Convenient for the pharmaceutical firms, no? These initial reactions are simply withdrawal responses, caused by the drug, and which your doctor undoubtedly failed to tell you about when putting you on the drug in the first place. Take your time, get off the anti-depressants and deal with the depression via talk therapy, exposure to sunshine, plenty of water and daily exercize. That will, in most cases, actually cure the depression, whereas the drugs simply mask the symptoms.
Wait until you've been off any kind of SSRI for a month or more, AND have the right mood. Mushrooms will amplify your mood, so don't ever trip in an effort to feel better or escape from unpleasant surroundings. I can't emphasize that enough, especially for someone with chronic, clinical depression. They will NOT make you feel better if you're depressed.
Shrooms also have a built-in defense against being abused. If you try to trip frequently, you'll find you have less and less effect from taking more and more shrooms. The shroom knows best . . . space those trips out, and allow yourself time to integrate what you learned from one trip before trying to take another.