The purpose of this research study is to evaluate the safety, tolerability, effectiveness, and pharmacokinetics (PK) of twice daily oral doses of V81444 in adults with ADHD. Pharmacokinetics (PK) is the study of how a drug is absorbed, distributed, metabolized, and eventually eliminated by the body. Pharmacokinetics is what the body does to the drug. Blood samples will be taken throughout the study for PK analysis.