I watched a movie where some woman was being haunted by a demon. I think it appeared as a human man with a painted face.
During a writing exercise of some kind, a teacher or professor tells the people present to write a letter to someone that has been troubling them and to do something with the letter. I think it was to burn it or destroy it in another way, though I'm not sure. The woman writes her letter to the demon, saying that she has convinced herself that it doesn't exist. I think the writing was in English, so this was either a British or American movie, most likely.
I don't remember the rest of the movie except for the ending. In the end, the woman is in a house along with a couple other people. They strap her down to a hospital bed, draw a circle of salt around it, and put her on an IV drip. The demon appears and tells the woman to take his hand and give control over her body to him, then tells her that the other characters have given her a lethal dose of morphine. To the other characters, the woman remarks that her hand is going numb, at which point one of the other characters starts crying and asks her for forgiveness for what they have done. As the woman is about to go unconscious from the morphine, she takes the demon's hand and he possesses her.
The movie ends with the possessed woman going around killing the characters (Although, IIRC, the last shot is just that of a house, and we hear screams and the sound of bones breaking).