HTR3A and post-traumatic stress disorder: Mirtazapine (which promotes sleep via antagonism of serotonin 5HT2 and 5HT3, histamine H1, and alpha-1-adrenergic receptor antagonists), and alpha-1-adrenergic antagonists such as prazosin can also be indicated (off-label use), being an antihypertensive agent used in the treatment of nightmares and sleep disturbances in patients with posttraumatic stress disorder (PTSD).