The primary aim of this study is to assess whether naltrexone as a monotherapy is effective in treating Attention Deficit Hyperactivity Disorder (ADHD) in adults. Medications that increase dopamine are often effective in treating ADHD in adults. Since naltrexone is a kappa opioid receptor antagonist, it increases dopamine in the brain.

We predict that naltrexone as a monotherapy will be effective for ADHD symptoms in adults with ADHD.

Inclusion Criteria

• Male and female outpatients 18-55 years of age.
• Diagnosis of ADHD, by DSM-IV by clinical evaluation by an expert clinician.
• Subjects treated for anxiety disorders and depression who are on a stable medication regimen for at least one month, and who have a disorder-specific CGI-Severity score ≤ 3 (mildly ill) and who have a score on the Hamilton-Depression and Hamilton-Anxiety rating scales below 15 (mild range).

Exclusion Criteria

• Any clinically unstable psychiatric conditions including any history of psychosis or mania, suicidality, sociopathy, criminality, or delinquency.
• Current (last 3 months) substance use disorders (alcohol or drugs),
• Medical condition or treatment that will either jeopardize subject safety or affect the scientific merit of the study including cardiovascular disease, current untreated hypertension, history of renal or hepatic impairment, or a condition that will or may require treatment with opioid analgesics.
• Clinically significant abnormal baseline laboratory LFT's, which is defined as LFT's greater than the ULN.
• Mental retardation (IQ < 80).
• Organic brain disorders including delirium, dementia, seizures, stroke, neurosurgery, and head trauma with loss of consciousness.
• Pregnant or nursing females.
• Subjects with current adequate treatment for ADHD.
• Current treatment with medication for ADHD.
• Any other concomitant medication with primarily central nervous system activity other than specified in the protocol (a stable and effective treatment regimen of an SSRI or benzodiazepine is permitted per clinical review.)
• A Clinical Global Impression (CGI) of 7 (among the most extremely ill patients) at the screening visit is exclusionary, and any subject who presents a CGI-S of 7 at any point during the study will be removed from participation.
• Subjects presenting with a CGI-Severity score of 6 (severely ill) at two consecutive visits after week 2 will be dropped from the study (i.e. A subject with a CGI of 6 at his/her week 3 visit and at week 4 visit will be dropped from the study at the week 4 visit). Subjects who are dropped for severe or worsening symptoms after exposure to the study medication will receive free follow up care as described in the detailed protocol and protocol summary.
• Non-English speaking subjects