The autonomic or automatic nervous system helps control blood pressure. Diseases of the
autonomic nervous system may result in a drop in blood pressure on standing in many cases
leading to fainting. Diseases that affect the autonomic nervous system include pure autonomic
failure, multiple system atrophy and Parkinson's disease, and can present with very similar
symptoms and it is sometimes difficult to determine an exact diagnosis. The purpose of the
study is to find out if the blood pressure response from taking a single dose of the
medication atomoxetine can help in the diagnosis of these diseases.