Aim at yourself, think of something, and pull the trigger

You think it would be morally questionable to use it on someone else, even if it most likely doesn't work, so you go to your room, close the door and look at the gun.

You ponder for a few moments what you should think of before you decide what to try. You pull the trigger and aim it at your other arm, in case it actually is dangerous you'd hate to accidentally kill yourself, and hear a humming sound charging up.

The world disappears into whiteness, and slowly returns like you've been flashbanged, but without the high pitched sound of your ears being broken by a loud bang. When you open your eyes, you notice things have changed, dramatically. For example, when you look in the mirror, you see: