Inclusion Criteria:

1. Men and women with idiopathic Parkinson’s Disease, as defined by UK Brain Bank Criteria.
2. Adults, ages 21 to 65 years old.
3. Clinically significant executive dysfunction, as defined by the reported presence of problems with disorganization, distractibility, task completion, planning or problem solving that represents a decline from premorbid (pre-PD) status and is confirmed by the patient’s informant.
4. Mini-Mental State Exam (MMSE) score > 26.
5. Absence of Dementia due to Parkinson’s Disease, as defined by DSM-IV-TR.
6. Clinical Dementia Rating (CDR) Scale score < 1.
7. Functional Assessment Staging (FAST) score < 4.
8. Hamilton Depression Rating Scale (HDRS) Score < 11.
9. Able to provide informed consent and participate in follow-up visits during the 8-week study duration.
10. Availability of informant who knows the patient well and is willing to provide collateral information on the patient’s clinical status and response to treatment.
11. On stable antiparkinsonian therapy for 3 months.
12. Any stage of PD severity, e.g., Hoehn and Yahr stage I-V, but must be able to participate in testing battery and be capable of independent function so as to manifest executive dysfunction.
13. Stable medical health with stable medication regimen for 3 months.
14. If history of major depression or anxiety disorder, must have stable symptoms and be on stable therapy for 3 months.
15. For women of childbearing potential, negative pregnancy test and reliable use of contraception.

Exclusion Criteria:

1. Prior exposure to atomoxetine within the last 6 months.
2. Current problems with urinary hesitancy or urinary retention.
3. Uncontrolled hypertension or tachycardia.
4. Narrow angle glaucoma.
5. Current presence of hallucinations without insight or uncontrolled delusions (patients with benign visual hallucinations of any sensory modality with insight, e.g., passage or presence hallucinations, or controlled stable delusions will be enrolled).
6. Illicit substance use or alcohol abuse or dependence within the last 6 months.
7. Current symptomatic Major Depressive Disorder or Anxiety Disorder that warrants additional treatment, as assessed on clinical interview, or 21-item Hamilton Depression Scale > 10.
8. For women, current pregnancy or nursing.
9. Current use of potent CYP2D6 inhibitors, e.g., paroxetine, fluoxetine, quinidine.
10. Current use of stimulant or wakefulness therapy, e.g., methylphenidate or modafinil.
11. Current hepatic dysfunction, defined as values of two times or greater than the upper limit of normal on the AST or ALT hepatic enzymes or any disorder affecting the liver that in the opinion of the enrolling investigator would interfere with hepatic metabolism of the medication or interfere with the participant’s ability to complete the study.
12. Current use of monoamine oxidase inhibitors that are typically used for treatment of depression (isocarboxazid, phenelzine, and tranylcypromine).