I really did not like taking medications as a psychic/medium because of the way it implies that I am schizophrenic, I am sick, I am mentally ill, I am schizoaffective. But! For some reason, and most likely because medications have different purposes, they have helped me a bit. No, your gift's won't be blocked. You might experience sometimes some tiredness from the medication's side effects, or as I have heard but not have verified as truth that medications can bring in negative energies to you and weaken your aura. But so far, my more and more recent experiences with medications have been positive.
Why do you want them blocked? And there are affirmations to help block out certain things like other's thoughts and spirits and ghosts.
I guess you can try, "I am a psychic/medium, thank you." That should block out negative energies and unwanted energies from you and other spirits and ghosts that are not wanted. You'll be fine! If you want to open your gifts up again, try the affirmation, "I am a psychic/medium, thank you for letting me see, hear, feel, smell, and taste ghosts, spirits, angels, spirit guides, nature spirits, elementals, the future, the past, the present, and thought's so I can help others."