A Clinical Study of Patients With Symptomatic NOH to Assess Sustained Effects of Droxidopa Therapy

Inclusion Criteria: * 1\. 18 years and older and ambulatory (defined as able to walk at least 10 meters); 2\. Clinical diagnosis of symptomatic orthostatic hypotension associated with Primary Autonomic Failure (PD, MSA and PAF), Dopamine Beta Hydroxylase Deficiency; 3\. At the Baseline visit (Visit 2), patients must demonstrate: 1. a score of at least 4 or greater on the Orthostatic Hypotension Symptom Assessment (OHSA) Item #1; 2. a fall of at least 20 mmHg in their systolic blood pressure, within 3 minutes of standing; 4\. Provide written informed consent to participate in the study and understand that they may withdraw their consent at any time without prejudice to their future medical care; Exclusion Criteria: * 1\. Score of 23 or lower on the mini-mental state examination (MMSE); 2\. Concomitant use of vasoconstricting agents for the purpose of increasing blood pressure; 1. Patients taking vasoconstricting agents such as ephedrine, dihydroergotamine, or midodrine must stop taking these drugs at least 2 days or 5 half-lives (whichever is longer) prior to their baseline visit (Visit 2) and throughout the duration of the study; 3\. Known or suspected alcohol or substance abuse within the past 12 months (DSM-IV definition of alcohol or substance abuse); 4\. Women who are pregnant or breastfeeding; 5\. Women of child bearing potential (WOCP) who are not using at least one method of contraception with their partner; 6\. Male patients who are sexually active with a woman of child bearing potential (WOCP) and not using at least one method of contraception; 7\. Untreated closed angle glaucoma; 8\. Diagnosis of hypertension that requires treatment with antihypertensive medications (short-acting antihypertensives to treat nocturnal supine HTN are allowed in this study) Any significant uncontrolled cardiac arrhythmia; 9\. History of myocardial infarction, within the past 2 years; 10\. Current unstable angina; 11\. Congestive heart failure (NYHA Class 3 or 4); 12\. History of cancer within the past 2 years other than a successfully treated, non-metastatic cutaneous squamous cell or basal cell carcinoma or cervical cancer in situ; 13\. Gastrointestinal condition that may affect the absorption of study drug (e.g. ulcerative colitis, gastric bypass); 14\. Any major surgical procedure within 30 days prior to the Baseline visit (Visit 2); 15\. Previously treated with droxidopa within 30 days prior to the Baseline visit (Visit 2); 16\. Currently receiving any other investigational drug or have received an investigational drug within 30 days prior to the Baseline visit (Visit 2); 17\. Any condition or laboratory test result, which in the Investigator's judgment, might result in an increased risk to the patient, or would affect their participation in the study; 18\. The Investigator has the ability to exclude a patient if for any reason they feel the subject is not a good candidate for the study or will not be able to follow study procedures.