Tasimelteon, sold under the brand name Hetlioz, is a medication approved by the U.S. Food and Drug Administration (FDA)[3] in January 2014, for the treatment of non-24-hour sleep–wake disorder (also called non-24, N24 and N24HSWD).

[13] In 2010, the FDA granted orphan drug status to tasimelteon, then regarded as an investigational medication, for use in totally blind adults with N24HSWD.

[4] In the opinion of Public Citizen, an advocacy group, the FDA erroneously allowed it to be labelled without stating that it is only approved for use by totally blind people.

[16] However, FDA updated its press release on Oct. 2, 2014 to clarify the approved use of Hetlioz, which includes both sighted and blind individuals.

[18] Experiments with rodents revealed fertility impairments, an increase in certain cancers, and serious adverse events during pregnancy at dosages in excess of what is considered the "human dose".