Droxidopa is a synthetic amino acid precursor which acts as a prodrug to the neurotransmitters norepinephrine (noradrenaline) and epinephrine (adrenaline). Unlike norepinephrine and epinephrine themselves, droxidopa is capable of crossing the protective blood–brain barrier (BBB). Droxidopa is a prodrug of norepinephrine and epinephrine used to increase the concentrations of these neurotransmitters in the body and brain. Patients with NOH have depleted levels of norepinephrine and epinephrine which leads to decreased blood pressure or hypotension upon orthostatic challenge. Droxidopa works by increasing the levels of norepinephrine and epinephrine in the peripheral nervous system (PNS), which induces tachycardia or increased heart rate and hypertension or increased blood pressure, thus enabling the body to maintain blood flow upon and while standing.