Studies have shown that individuals with attention deficit hyperactivity disorder (ADHD) are at greater risk for having a substance use disorder compared to people who do not have ADHD. Rates of cocaine abuse in adults with ADHD are significantly higher than they are in adults who do not have ADHD. Some clinicians suggest that adults with ADHD may abuse cocaine in order to self-medicate their ADHD symptoms. Atomoxetine is a drug that has been effective in treating ADHD. This study will evaluate the effectiveness of atomoxetine in reducing cocaine use in people with ADHD who abuse cocaine.