The US Food and Drug Administration (FDA) in January approved Vanda Pharmaceuticals' Hetlioz (tasimelteon), the first drug to treat non-24 sleep-wake disorder. The condition, known as non-24, is common in totally blind people with no light perception, who lack the environmental cues to synchronize their endogenous circadian rhythm with the day-night cycle. Hetlioz is a small-molecule agonist for type 1 and 2 melatonin receptors, known to play a key role in regulating circadian rhythms. Off-the-shelf melatonin (N-acetyl-5-methoxytryptamine) formulations are sold as food supplements in the US, claiming to promote sleep and ease jet lag. They have also been used to treat non-24. But dosage of these melatonin preparations varies widely, and efficacy is unreliable. In addition, no clinical trials have tested melatonin's efficacy in non-24. Phase 3 study results with Hetlioz show that if taken once daily at the same time before bedtime, the drug improves sleep-wake parameters, such as total sleep time and timing of sleep. Non-24, which can cause disrupted sleep-wake patterns and excessive daytime sleepiness, affects 80,000–100,000 people in the US. Morningstar, a Chicago-based independent investment research company, estimates $600-million peak sales for Hetlioz. “We assume that it's going to be a slow wrap-up,” says Morningstar analyst Stefan Quenneville, “which [comes] down to two main reasons: Vanda is a small biotech without the marketing heft behind them and non-24 is a relatively new indication.” Vanda, located in Washington, DC, has launched an active outreach program to increase awareness of non-24, and commercial launch is slated for the second quarter of this year.