Treatment-emergent adverse events will be summarized by presenting the number and percentage of patients having any treatment-emergent AE, having an AE in each body system, and having each individual AE.

Entrainment is a measure of synchronization of the master body clock to the 24-hour day. The circadian period (τ) was calculated using urinary aMT6s collected over four separate 48 hour periods, approximately 1 week apart, during the run-in and randomized phases of the trial. Maintenance of entrainment is defined as the proportion of subjects who become non-entrained to a 24 hour day after randomization to tasimelteon or placebo. Non-entrainment was defined as having a post-baseline τ value ≥ 24.1 or the lower bound of the 95% CI \>24.0.

Entrainment is a measure of synchronization of the master body clock to the 24-hour day. The circadian period (τ) was calculated using urinary aMT6s collected over four 48 hour periods , collected approximately 1 week apart for 4 separate weeks, during the screening and month 1 of the randomization phase of the trial. Entrainment was defined as having a post-baseline τ value less than 24.1 and a 95% CI that included 24.0.

Clinical response is defined as the coincident demonstration of entrainment (aMT6) and a score ≥ 3 on the Non-24 Clinical Response Scale (N24CRS). N24CRS measures improvement in sleep-wake measures and overall functioning (LQ-nTST, UQ-dTSD, MoST and CGI-C). Each assessment is scored as a 1 or 0 depending on the pre-specified threshold (see below). LQ-nTST: \>45 minutes increase in average nighttime sleep duration; UQ-dTSD: \>45 minutes decrease in average daytime sleep duration; MoST: \>30 minutes increase and a standard deviation \<2 hours during double-masked phase (6 months); CGI-C: \<2.0 from the average of D112 and Day 183 compared to baseline For patients randomized to tasimelteon 20 mg and who also participated in the screening phase of Study 3203 (month 7 of treatment), the screening τ from Study 3203 was used if the patient did not become entrained in Study 3201 but did become entrained during the screening phase of Study 3203.