A clinical study has raised concerns about next-day impairment from a widely used sleep medication.

Researchers at Flinders University in Adelaide, Australia, examined how a single nighttime dose of quetiapine, an antipsychotic often prescribed off-label for sleep issues, affected driving performance the following morning.

The small randomized controlled trial, published in the Annals of the American Thoracic Society, involved 15 adults with obstructive sleep apnea who also struggled with maintaining sleep.

Each participant completed two overnight sessions spaced about one week apart.

On one night, participants took 50 milligrams of quetiapine before bed. On the other, they received a placebo.

During the study, researchers monitored breathing patterns, brain activity, oxygen levels, and leg movements while participants slept.

People who took the medication had notable improvements: their total sleep time increased by more than 40 minutes, and wakefulness during the night decreased by 45%. Apnea-related events also dropped from 27 to 20 per hour.

However, when participants were tested on a driving simulator within 30 minutes of waking, their morning alertness told a different story.

Those who took quetiapine showed slower reaction times and made more mistakes, including drifting out of their lane more often than when they took the placebo.

Participants also performed worse on a 10-minute reaction time test, and attention lapses more than tripled compared to the placebo session.

Although 11 of the 15 participants reported feeling sleepier the next morning, about one in four did not recognize how impaired they were.

Researchers noted that this unawareness increased the risk of unsafe activities such as driving or operating machinery too soon after waking.

Mild to moderate side effects were also observed among users of quetiapine, including nausea, restless legs, and a sudden drop in blood pressure upon standing, which affected one in three participants.

The scientists acknowledged several limitations, including the small sample size and the single-night evaluation, which may not represent real-world conditions. They called for larger, long-term studies to confirm their findings.

Until more data is available, the research team recommended that people who take quetiapine avoid driving or performing safety-critical tasks for at least 9.5 hours after dosing.

Ashley Curtis, PhD, director of the Cognition, Aging, Sleep and Health Lab at the University of South Florida, said the results highlight an important aspect of how such medications affect men and women differently.

Women typically metabolize some sleep drugs more slowly, which may increase the risk of next-day effects, she explained.

Curtis emphasized that future research should look closely at these sex-specific patterns to ensure safe dosing.

She added that quetiapine’s effects on next-day cognitive function should be studied further, especially among older adults who may already be at higher risk for side effects from multiple medications.

Curtis also pointed out that insomnia often develops from learned behavioral factors, and although medications can provide short-term relief, long-term management usually benefits from therapies such as cognitive behavioral treatment for insomnia.

Chelsie Rohrscheib, head sleep expert at Wesper, a New York–based sleep analysis company, said the findings should not cause alarm but should prompt careful discussions between patients and their physicians.

People taking quetiapine for sleep, especially if they have sleep apnea or wake feeling groggy, should consider whether the advantages outweigh the potential risks, she said.