There is a story I believe posted @ Storysite where an aunt tries to cope with a visiting nephew's smoking pot, and involvement with the pot crowd. She tells him that if he continues to do pot, that he will develop as a girl.

He stops, but because of his friends, she wrongfully thinks that her nephew is doing pot and has him feminized by a doctor. She later on has him totally sex changed because she thinks that her niece is still doing pot.

Only after her niece is totally a girl, does the aunt know the truth. by then, her nephew is traumatized into being a girl, and looks forward to sex with guy.