Tasimelteon

Tasimelteon (VEC-162, BMS-214778) is an orally active, selective dual agonist of the melatonin MT1 and MT2 G-protein-coupled receptors, approved by the United States Food and Drug Administration for the treatment of Non-24-Hour Sleep-Wake Disorder (Non-24) in totally blind individuals (January 2014) and for the treatment of nighttime sleep disturbances associated with Smith-Magenis Syndrome (December 2020). The compound is marketed by Vanda Pharmaceuticals under the trade name Hetlioz and was originally synthesized at Bristol-Myers Squibb as BMS-214778 before being licensed to Vanda in 2004 for clinical development. Tasimelteon is a circadian regulator that resets the master body clock in the suprachiasmatic nucleus of the hypothalamus by engaging both melatonin receptor subtypes, with approximately 2.1- to 4.4-fold greater affinity for the MT2 receptor (Ki approximately 0.07 to 0.17 nM) than for the MT1 receptor (Ki approximately 0.30 to 0.35 nM). The compound and its major metabolites have no appreciable affinity for more than 160 other pharmacologically relevant receptors, including gamma-aminobutyric acid, serotonin, noradrenaline, acetylcholine, dopamine, and opiate receptor systems, conferring a remarkably clean selectivity profile among circadian-active agents.

The clinical evidence base for tasimelteon rests principally on two pivotal Phase 3 trials (SET and RESET), published in The Lancet in 2015, which demonstrated that 20 mg of oral tasimelteon administered nightly entrained the circadian pacemaker in totally blind individuals with Non-24 and that continued treatment was necessary to maintain entrainment. In the SET trial, tasimelteon achieved the co-primary endpoints of circadian entrainment of the melatonin rhythm and clinical response compared with placebo. In the RESET withdrawal trial, patients randomized to placebo after an entrainment run-in period showed significant deterioration in nighttime sleep, daytime sleep, and timing of sleep, while patients maintained on tasimelteon preserved their clinical benefit. A supplemental indication for Smith-Magenis Syndrome was approved in December 2020 based on a randomized, double-blind, placebo-controlled crossover study demonstrating improvement in nighttime sleep disturbances in both adults and children with this rare neurodevelopmental disorder characterized by an inverted circadian melatonin rhythm. A supplemental application for jet lag disorder has been twice rejected by the FDA (in 2019 and again in January 2026 upon re-review), despite court-ordered reconsideration by the DC Circuit Court of Appeals.

Pharmacokinetics are characterized by rapid oral absorption (Tmax 0.5 to 3 hours), moderate oral bioavailability (approximately 38 percent), high plasma protein binding (approximately 90 percent), a short elimination half-life (1.3 hours), and extensive hepatic metabolism primarily through CYP1A2 and CYP3A4 oxidation pathways. The short half-life distinguishes tasimelteon from melatonin itself and from ramelteon and reflects the rapid clearance of the parent compound, with the chronobiotic effect being mediated by the timing of receptor occupancy rather than sustained plasma exposure. Eighty percent of an administered dose is recovered in urine as metabolites, with less than 1 percent excreted as unchanged parent compound. The five most abundant metabolites (M9, M11, M12, M13, M14) retain binding activity at the MT1 and MT2 receptors but at less than one-tenth the affinity of the parent compound. Clinically significant drug interactions include a 7-fold increase in exposure with fluvoxamine (a strong CYP1A2 inhibitor), a 90 percent decrease in exposure with rifampin (a strong CYP3A4 inducer), and an approximately 40 percent decrease in exposure in tobacco smokers (reflecting CYP1A2 induction). Elderly patients (older than 65 years) exhibit approximately 2-fold higher exposure than younger adults.

This monograph reviews the chemistry, synthesis, and stereochemistry of tasimelteon; the dual melatonin receptor agonist pharmacology and circadian mechanism; the comprehensive human pharmacokinetic record including drug-drug interactions and special populations; the preclinical chronobiology; the clinical evidence base across Non-24, Smith-Magenis Syndrome, jet lag disorder, and insomnia indications; sourcing and quality verification for research applications; reconstitution and handling; stack-interaction considerations; adverse-event signal; and a structured comparative assessment of five melatonin receptor agonists and related circadian agents (ramelteon, prolonged-release melatonin, agomelatine, suvorexant, and melatonin) against tasimelteon on five competency standards (novelty, effect size, promising potential, side-effect profile, and overall validation).