The central nervous system is in an ever-adjusting balance between inhibition and excitation. Ambien, like alcohol or an anesthetic, triggers the brain’s main inhibitory system, which depends on binding between gaba—gamma-aminobutyric acid, a neurotransmitter—and gaba receptors on the surface of billions of neurons. gaba receptors can be found throughout the brain, and when they’re activated the brain slows. Ambien encourages the process by sticking to the receptors, holding open the door to the neurotransmitter. Suvorexant, which Merck describes as “rationally designed”—rather than stumbled upon, like most drugs—influences a more precise set of neurotransmitters and receptors. Orexin neurotransmitters, first identified fifteen years ago, promote wakefulness. When suvorexant is in the brain, orexin is less likely to reach orexin receptors. Instead of promoting general, stupefying brain inactivity, suvorexant aims at standing in the way of a keep-awake signal. This difference may or may not come to mean a lot to insomniacs, but Merck’s marketing is likely to encourage the perception that suvorexant ends the dance by turning off the music, whereas a drug like Ambien knocks the dancer senseless.

via Ian Parker: The Search for a Blockbuster Insomnia Drug : The New Yorker.