Shift Work Sleep Disorder Guide

When a work schedule runs against the body clock, the cost to sleep and alertness can become a diagnosable disorder.

Shift work sleep disorder is a circadian rhythm disorder in which a recurring work schedule that overlaps the usual time for sleep, such as night, early-morning or rotating shifts, causes insomnia, excessive sleepiness, or both, for at least three months.¹ A pooled analysis of 29 studies put it at about one in four people who work shifts.² It is diagnosed clinically, from a sleep history and sometimes a sleep diary, rather than a lab test. Treatment combines timed light, planned naps and protected daytime sleep with medication where needed. Modafinil is FDA-approved for the excessive sleepiness it causes, and in the trial behind that approval it reduced sleepiness and attention lapses without fully restoring alertness.^3,4,5

When the Schedule Fights the Clock

The body runs on an internal clock of roughly 24 hours, set mainly by light. It schedules alertness for the day and sleep for the night. Night and early-morning work ask for the opposite: wakefulness when the clock is pushing hardest toward sleep, and sleep when it is signaling day.³

The result is twofold. Sleep taken during the day tends to be shorter and more broken, and the hours before dawn bring the strongest pull toward sleep at work. In 2017 and 2018, 16% of US wage and salary workers usually worked a schedule other than a regular daytime one.⁶ See circadian rhythms for how the biological clock works.

Ordinary Strain or a Disorder

Almost everyone who works nights or irregular shifts feels it. Clinicians look for persistence and impact:¹

Tied to the schedule. Insomnia, excessive sleepiness, or both, along with shortened sleep, linked to a work schedule that overlaps the usual time for sleep.

Lasting three months or more. A rough week after a rotation is not the disorder.

Not better explained by something else. Another sleep disorder, a medical condition or a medication.

Schedule matters. In one random population sample, 32.1% of night workers met criteria for shift work disorder, against 10.1% of day workers.⁷

What It Does Beyond Tiredness

On the drive home. In a closed-track study of 16 night-shift workers, 37.5% of drives after a night shift involved a near crash, compared with none after a night of sleep.⁸

On the heart. A meta-analysis of 34 studies covering about 2 million people linked shift work to a 23% higher risk of heart attack.⁹

Neither finding is limited to people with the disorder, but both show what is at stake when a schedule disrupts sleep.

How It Is Diagnosed

There is no blood test or scan for shift work disorder. A clinician takes a sleep history covering the work schedule, when and how long you sleep, and how sleepy you are on shift.¹ The clinician also looks for other explanations, such as deliberately short sleep, alcohol or depression, before putting the sleepiness down to the schedule.¹ Because sleep apnea and other conditions also cause sleepiness, symptoms such as loud snoring or pauses in breathing call for separate testing. See obstructive sleep apnea.

How It Is Treated

The American Academy of Sleep Medicine’s practice parameters recommend a combination of measures, with medication alongside them rather than instead of them.³

Planned naps. A nap before or during a night shift improves alertness and performance on shift.

Timed light. Bright light during the shift and limited light exposure in the morning improve alertness at work.

Caffeine. An option for alertness during the night shift.

Protected daytime sleep. A dark, quiet room, and melatonin taken before daytime sleep for some people. Sleep medication can also be used to support daytime sleep, under a clinician’s direction. Practical detail is in the shift worker’s guide to better sleep.³

Modafinil. Modafinil is FDA-approved to improve wakefulness in adults with excessive sleepiness associated with shift work disorder, and the AASM practice parameters name it for improving alertness during the night shift.^3,4

In the three-month trial behind that approval, 209 people with shift work disorder took modafinil or a placebo before each night shift. Clinicians rated 74% of those on modafinil as improved, against 36% on placebo. Lapses of attention on a reaction-time test fell on modafinil and rose on placebo. Fewer people taking modafinil reported an accident or near accident on the drive home: 29%, compared with 54% on placebo.⁵

The same trial is clear about the limits. People taking modafinil still had excessive sleepiness and impaired performance at night, so it narrows the gap rather than closing it, and it does not make driving after a shift safe.^4,5 Headache is its most common side effect; modafinil side effects and safety covers rare serious rashes and the interaction with hormonal birth control.⁴

Getting Evaluated

If sleepiness on shift or poor daytime sleep has lasted three months or more despite the measures above, an evaluation can establish whether shift work disorder is the cause and which treatment fits. Bring a list of current medications. Not every evaluation ends in a prescription.