I've been on prazosin for2.5 years. I take mg at bedtime along with 30mg mirtazipine. I feel like the prazosin is no longer working. Flashbacks are back to being stronger however there are fewer as I keep stresss levels lower. I take propranolol when needed but I think I may talk to dr about trying without prazosin for awhile it makes my heart race and prazosin can have negative affect on sinuses. Has anyone else lost effectiveness of prazosin?