Prazosin is an antihypertensive (blood pressure) medicine that can remove nightmares. It does work. It was found to do that because war veterans were given it for high blood pressure and started saying things like "the nightmares have stopped." They kept reducing the dose and it still works at 1mg and most peoples' blood pressure doesn't go too low at that dose. Took away the same nightmare I had every night for over two decades. I have since stopped it and don't have that horror any more. Other changes in my life changed my dreams too, but prazosin was a huge help.
I also had to stop melatonin more recently because I found it was causing overly vivid dreams and I wasn't walking up rested.