Prevention of Stimulant-Induced Euphoria With an Opioid Receptor Antagonist

Inclusion 1. Male and female outpatients 2. age 18-30 3. diagnosis of ADHD by DSM-IV, per clinical evaluation and confirmed by structured interview 4. likeability response (\> 5) on Question #2 of the DRQ-S after an initial test dose of 60 mg of IR MPH. 5. Baseline ADHD severity of \> 20 on the Adult ADHD Investigator System Report Scale (AISRS) 6. Able to participate in blood draws and to swallow pills. 7. Subjects must be considered reliable reporters, must understand the nature of the study and must sign an informed consent document Exclusion 1. Any current (last month), non-ADHD Axis I psychiatric conditions 2. Ham-D \> 16, BDI \> 19, or Ham-A \> 21 3. Any clinically significant chronic medical condition 4. any cardiovascular disease or hypertension 5. Clinically significant abnormal baseline laboratory values 6. I.Q. \< 80) 7. Organic brain disorders 8. Seizures or tics 9. Pregnant or nursing females 10. Clinically unstable psychiatric conditions (i.e. suicidal behaviors, psychosis) 11. Current or recent (within the past year) substance abuse/dependence 12. patients on other psychotropics 13. Current or prior adequate treatment with MPH 14. known hypersensitivity to methylphenidate 15. Current opioid use (by history and urine screen) or potential need for opioid analgesics during the study 16. acute hepatitis or liver failure (baseline blood tests).