TD-9855 Phase 2 in Neurogenic Orthostatic Hypotension (nOH)

Inclusion Criteria: * Diagnosed with symptomatic orthostatic hypotension due to Parkinson's disease, multiple system atrophy, or pure autonomic failure, (i.e. neurogenic orthostatic hypotension). * At screening, subject must meet the diagnostic criteria of neurogenic orthostatic hypotension, as demonstrated by a ≥ 30 mm Hg drop in systolic blood pressure (SBP) within 5 minutes of standing. * Impaired autonomic reflexes, as determined by absence of BP overshoot during phase IV of the Valsalva maneuver, in subjects where Valsalva is performed, as appropriate. * For the optional open-label extension study subjects must have demonstrated a pressor effect and completed dosing in Part A. Exclusion Criteria: * Systemic illnesses known to produce autonomic neuropathy, including but not limited to diabetes mellitus, amyloidosis, monoclonal gammopathy of unknown significance, and autoimmune neuropathies. * Concomitant use of vasoconstricting agents for the purpose of increasing BP such as ephedrine, dihydroergotamine, or midodrine must be stopped at least 2 days or five half lives (whichever is longer) prior to dosing on Day 1 of Part A and C, and throughout the duration of Part C. Subjects previously enrolled in Part A under previous versions of the protocol will continue taking fludrocortisone during the washout period and in Part C at the dose and regimen used in Part A. For new subjects enrolling in Part A under Amendment 3, fludrocortisone use in both Parts of the study and dur…