Eszopiclone

Eszopiclone is a nonbenzodiazepine hypnotic, one of the so-called Z-drugs developed as alternatives to older benzodiazepine sleeping pills ^[1][2]. Chemically it is a cyclopyrrolone and is the single active S-enantiomer isolated from zopiclone, a racemic hypnotic long used in other countries ^[1]. Although its chemical structure differs from that of the benzodiazepines, it acts on the same target in the brain, which is why it is grouped with them by mechanism ^[1].

Eszopiclone was developed by the pharmaceutical company Sepracor, later Sunovion, and was approved by the United States Food and Drug Administration in 2004 under the brand name Lunesta ^[1]. In Europe it was not granted status as a new active substance, with regulators judging it too similar to the already-available zopiclone ^[1]. It is now available generically ^[1]. In 2014, US regulators lowered the recommended starting dose after evidence that higher doses could impair alertness and driving the following morning ^[1].

Eszopiclone is used to treat insomnia, helping both with falling asleep and with staying asleep, and unlike some earlier hypnotics it has been studied for use over periods of several months ^[1][2]. A Cochrane review of randomized trials concluded that it produces moderate improvements, shortening the time to fall asleep, reducing time awake during the night, and increasing total sleep time, with little evidence of harm when taken as directed ^[2]. Broader analyses of the Z-drug class, however, found that the average improvement in the time taken to fall asleep, while genuine, is fairly small and accompanied by a sizable placebo response ^[3]. Reviews of sleep medicines in older adults urge particular caution, since these drugs are linked to daytime impairment, falls, and fractures in that group ^[4].

Eszopiclone is a prescription-only medicine taken as an oral tablet, and in the United States it is classified as a Schedule IV controlled substance because of its potential for misuse and dependence ^[1][2]. Its most distinctive side effect is an unpleasant, bitter or metallic taste; other common effects include headache, dry mouth, dizziness, and daytime drowsiness ^[1][2]. Less commonly, hypnotics of this kind have been associated with complex sleep behaviors such as sleep-walking or sleep-driving, and with next-day impairment, which is why the lowest effective dose is generally advised ^[1][4].

The headline risk is next-day impairment. Eszopiclone can linger long enough that driving, memory, and coordination are measurably worse the morning after, sometimes as long as 11 hours later, and people often don't feel how affected they are; in 2014 the FDA cut the recommended starting dose from 2 mg to 1 mg specifically to blunt this. Like all Z-drugs it can trigger complex sleep behaviors; sleep-driving, sleep-eating, or making calls while not fully awake with no memory of it, which prompted an FDA boxed warning in 2019. The most common everyday complaint is that unpleasant bitter or metallic taste (dysgeusia), alongside headache, dizziness, dry mouth, and daytime drowsiness.

It can cause psychological and physical dependence, with tolerance and rebound insomnia or withdrawal if stopped abruptly, so it's meant for short-to-intermediate use and is a Schedule IV controlled substance. The most dangerous mistake is stacking it with other central nervous system depressants; alcohol, opioids, benzodiazepines, or sedating antihistamines all add up and can cause heavy sedation, blackouts, slowed breathing, and overdose. Because it's cleared by CYP3A4, strong inhibitors of that enzyme (like ketoconazole or clarithromycin) push its blood levels up and make impairment worse.

Eszopiclone is metabolized primarily by cytochrome P450-3A (CYP3A4), and drugs that inhibit this enzyme can prolong its half-life and increase its plasma concentration ^[23]. This is a pharmacokinetic interaction; the inhibitor reduces eszopiclone clearance. CYP3A4 inhibitors such as ketoconazole, ritonavir, erythromycin, and some antidepressants would be expected to increase eszopiclone exposure and the risk of residual sedation and impaired driving performance the morning after dosing.

Eszopiclone also produces pharmacodynamic interactions with any other central nervous system depressants including alcohol, benzodiazepines, and opioids; these combinations raise the risk of excessive sedation. The half-life increase in elderly patients and those with hepatic disease follows the same mechanism as CYP3A4 inhibition; dose adjustment is recommended for these populations ^[23]. Interactions with mild-to-moderate CYP3A4 inhibitors, most antihistamines, and typical antacids have not been formally studied; the clinical significance of these pairings remains unclear.

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