Reoccurring Symbol in Shakespeare's Plays

While I was reading act I of Othello, I began to notice a trend in several of Shakespeare's plays. In all of the tragedies that I have read by him, he has somehow incorporated witchcraft or potions. (Now I don't have any direct quotes for most of these plays because I don't have copies of them with me, therefore all my arguments are from my own recollection of the plots.) In Romeo and Juliet, the two lovers end their lives by drinking a potion. Macbeth is more associated with witchcraft with all the influence the three witchs have on Macbeth's thought process. But if I recall correctly, it is through a potion that Macbeth is able to receive the three warnings from the witches as to how his power will be taken from him. Hamlet's father is killed by Hamlet's uncle when he pours a potion in his ear while he sleeps in the garden. We already see this repetition of witchcraft in Othello. Barabantio's first reaction when he hears that his daughter has married without his knowledge is "is there not charms (spells)" (I, 1, 173). I think Shakespeare used this reocurring symbol throughout his tragedies because during the time he wrote the dominating religions were Christianity and Muslim. Among these religions, especially in the Christian religion, many cults were arising that were very much into witchcraft and postions. Shakespeare was not a person of religion and therefore I believe the used these ideas from the cults in his writing. I have included two links: one to the life of Shakespeare http://en.wikipedia.org/wiki/William_Shakespeare and the other to popular cults of the Christian religion http://en.wikipedia.org/wiki/Witch_Hunters.