Evaluating the Effects of Tasimelteon Vs. Placebo in Delayed Sleep-Wake Phase Disorder (DSWPD) and the CRY1Δ11 Variant

Inclusion Criteria: * Ability and acceptance to provide written informed consent. * A confirmed clinical diagnosis of Delayed Sleep-Wake Phase Disorder (DSWPD). * Carrier of CRY1Δ11 variant. * Men or women between 18 - 75 years, inclusive. * Body Mass Index (BMI) of ≥ 18 and ≤ 40 kg/m\^2. Exclusion Criteria: * Major surgery, trauma, illness, general anesthesia, or immobility for 3 or more days within the last 30 days. * Pregnancy, recent pregnancy (within 6 weeks), or women who are breastfeeding. * A positive test for substances of abuse. * Current tobacco user.