Old horror movie (title needed)

[Wilcoxfan]

I can't remember what it was, but it was a movie. This mysterious figure in a hood would shoot darts into people. Once they got hit, they would get hallucinations and then think the images were real. It would cause them to kill themselves. I remember the opening scene, a man was hit my a dart and has these visions, then to escape, he jumped out of the window, killing himself.
I can't remember anything else from the movie. Does anyone else know what I'm talking about?