Phase III Trial Yields Positive Results for Delayed Sleep-Wake Phase Disorder Drug Candidate

By FitNews On Oct 1, 2026

Key takeaways:

A phase III study of Hetlioz (tasimelteon) met its primary endpoint, with the circadian regulator shifting sleep onset 42.5 minutes earlier compared to a 5.4-minute shift on placebo.
An exploratory analysis showed 60% of treated participants advanced their sleep timing by at least 30 minutes, compared to 15% in the placebo group.
The developer plans to submit a supplemental New Drug Application to the FDA; if cleared, it would become the first FDA-approved treatment for delayed sleep-wake phase disorder.

Vanda Pharmaceuticals Inc recently shared positive topline results from its pivotal phase III study of Hetlioz (tasimelteon) 20 mg in adults with delayed sleep-wake phase disorder.

Vanda intends to discuss these data with the US Food and Drug Administration (FDA) and to submit a supplemental New Drug Application (sNDA) seeking approval of Hetlioz for delayed sleep-wake phase disorder. If approved, the drug would be the first FDA-approved medicine indicated for this condition.

Hetlioz is an already approved circadian regulator. The FDA first approved it in 2014 to treat non-24-hour sleep-wake disorder in adults, and in 2020 to treat nighttime sleep disturbances in people with Smith-Magenis syndrome. The delayed sleep-wake phase disorder program would extend that same medicine, at the same 20 mg dose, to a third circadian sleep-wake disorder.

The multicenter, double-blind, randomized, placebo-controlled phase III study evaluated adults 18 to 75 years of age with a confirmed clinical diagnosis of delayed sleep-wake phase disorder. Participants received once-daily oral tasimelteon 20 mg or a matching placebo for 28 days. The study evaluated over 260 individuals and enrolled a total of 43 patients with delayed sleep-wake phase disorder across 26 clinical sites in the US and Europe over more than five years.

The study met its primary endpoint, which was the start time of the sleep episode as measured by a sleep diary. Hetlioz 20 mg (n=20) shifted the time of sleep onset 42.5 minutes earlier, compared with a 5.4-minute shift on placebo (n=20)—a 37.1-minute difference (p=0.022).

In an exploratory responder analysis, 60% of tasimelteon-treated participants advanced their sleep timing onset by at least 30 minutes, compared with 15% on placebo (p=0.008).

Safety over the 28-day controlled period was consistent with the established Hetlioz label, and no new safety signals were identified.

Delayed sleep-wake phase disorder is a body-clock disorder where the internal clock is stably set too late. People with the disorder often cannot fall asleep until the early morning hours, even when they get into bed at a conventional time, and subsequently cannot wake for work, school, or family life the next morning.

“People with [delayed sleep-wake phase disorder] often remain undiagnosed and undertreated, especially because of the absence of a proven approved treatment,” says Mihael H. Polymeropoulos, MD, president, CEO, and chairman of the board at Vanda Pharmaceuticals, in a release. “This study extends our knowledge of the clinical properties of Hetlioz as a versatile circadian regulator. We look forward to discussing these data with the FDA and pursuing a new indication for Hetlioz.”

The planned sNDA application is expected to include this phase III study alongside the company’s prior studies in related disorders and more than a decade of use in two approved circadian indications.

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