Prazosin hydrochloride is an alpha-adrenergic blocker and is a sympatholytic drug used to treat high blood pressure and anxiety, PTSD, and panic disorder. Target: Adrenergic Receptor Prazosin hydrochloride, is a sympatholytic drug used to treat high blood pressure and anxiety, PTSD, andpanic disorder. It is an alpha-adrenergic blocker that is specific for the alpha-1 receptors. These receptors are found on vascular smooth muscle, where they are responsible for the vasoconstrictive action of norepinephrine. They are also found throughout the central nervous system. As of 2013, Prazosin (hydrochloride) is off-patent in the US, and the FDA has approved at least one generic manufacturer. In addition to its alpha-blocking activity, Prazosin (hydrochloride) is an antagonist of the MT3 receptor (which is not present in humans), with selectivity for this receptor over the MT1 and MT2 receptors. Prazosin hydrochloride is orally active and has a minimal effect on cardiac function due to its alpha-1 receptor selectivity. However, when Prazosin (hydrochloride) is initially started, heart rate and contractility go up in order to maintain the pre-treatment blood pressures because the body has reached homeostasis at its abnormally high blood pressure. The blood pressure lowering effect becomes apparent when Prazosin (hydrochloride) is taken for longer periods of time. The heart rate and contractility go back down over time and blood pressure decreases.