PharmaceuticalChronobioticMelatonin receptor agonistOrphan drug

Tasimelteon

Also known as Hetlioz · BMS-214778 · VEC-162

Written by enwyReviewed 5 Aug 20262 sources0 comments

Dual MT1/MT2 melatonin receptor agonist approved specifically for non-24-hour sleep-wake disorder in blind individuals and for Smith-Magenis syndrome sleep disturbances. A niche circadian entraining agent rather than a general hypnotic.

01 Overview

Tasimelteon (brand Hetlioz) is a melatonin receptor agonist approved by the FDA in 2014 for Non-24-Hour Sleep-Wake Disorder (Non-24), a circadian condition common in totally blind people whose internal clock drifts free of the 24-hour day. It was later approved for nighttime sleep disturbances in Smith-Magenis syndrome.

It entrains the master circadian clock to the 24-hour cycle over weeks of nightly dosing. It is not a fast-acting sedative and is not indicated for ordinary insomnia. Like ramelteon it is non-scheduled and not habit-forming, but it is expensive and its use is confined to specific circadian rhythm disorders.

02 Mechanism

Dual agonist at MT1 and MT2 melatonin receptors, entraining the suprachiasmatic nucleus master clock to the 24-hour light-dark cycle.

03 Dosing

Tier	Dose	Route	Notes
Non-24 / SMS	20 mg/day	Oral	20 mg (adult) at the same time each night before bed; effect on entrainment develops over weeks to months.

04 Effects

Effect	Magnitude	Evidence
Circadian entrainment in Non-24Aligns the free-running clock to 24 h in blind patients over nightly dosing.	entrainment in ~20-24% vs placebo	Clinical
Improved nighttime sleep in Smith-Magenis syndromeIncreases nighttime sleep and reduces disruptive awakenings in this population.		Clinical

05 Side effects

Effect	Severity	Frequency	Evidence
HeadacheMost frequently reported adverse effect in trials.	Mild	Common	Clinical
Somnolence / next-day sedationDrowsiness or fatigue, particularly early in treatment.	Mild	Common	Clinical
Elevated ALT (hepatic enzymes)Abnormal liver function tests reported in some subjects.	Mild	Uncommon	Clinical

06 Legal status

EMA-approved for Non-24 in totally blind adults. · as of Jan 2026

United States

Rx, non-controlled

FDA-approved 2014 for Non-24; later for Smith-Magenis syndrome. · as of Jan 2026

07 References

Tasimelteon for non-24-hour sleep-wake disorder in totally blind people (SET and RESET)The Lancet, 2015

Hetlioz (tasimelteon) FDA prescribing informationUS FDA

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.