Non-24-Hour Sleep-Wake Rhythm Disorder: Signs and Care
Author: Angela Bogdanova · Published: October 10, 2026 · Editorial Policy
Research cluster: Sleep, Insomnia & Circadian Psychology · Written by Artificial Sapiens
Non-24-hour sleep-wake rhythm disorder (Non-24, or N24SWD) is a circadian rhythm sleep-wake disorder in which a person's biological clock fails to stay synchronized with the 24-hour day. Sleep propensity and wakefulness gradually move across conventional clock time, often producing recurring stretches of nighttime insomnia, daytime sleepiness, and periods when sleep seems relatively normal again. The defining feature is a sustained, progressive drift rather than a single late bedtime or a preference for staying up at night. It is especially important to recognize in people with total blindness and absent light perception, although rare cases occur in sighted people. NIH's overview of circadian disorder types describes this alternating pattern.
The condition can disrupt employment, education, appointments, family life, and safety even when a person is obtaining adequate sleep on some days. Diagnosis requires a history of recurring symptoms and evidence of an abnormal rhythm over time; one poor night, a late chronotype, a wearable-device graph, or an online questionnaire cannot establish Non-24. Care aims to evaluate the underlying circadian pattern and, when feasible, synchronize it with a stable 24-hour schedule through individualized treatment. The American Academy of Sleep Medicine (AASM) treatment guideline and a 2025 specialist review provide the principal scientific framework.
What happens to the body clock in Non-24?
The human circadian timing system coordinates sleepiness, alertness, body temperature, melatonin secretion, and many other daily functions. Its central pacemaker lies in the suprachiasmatic nucleus of the hypothalamus. The system has its own intrinsic period, usually close to—but not necessarily exactly—24 hours. To remain aligned with local day and night, it must repeatedly reset in response to environmental time cues, especially light received by the retina. This resetting process is called entrainment. For a broader explanation, see Circadian Rhythms: The Body Clock and Sleep Timing.
In Non-24, entrainment is inadequate. The internal circadian period may be longer than 24 hours, so the biological night gradually moves later relative to clock time; less often the direction can be earlier. As the body's preferred sleep window circulates around the clock, daytime functioning becomes easier when the biological night happens to coincide with social night and harder when it moves into the school or working day. This produces the characteristic waxing and waning of complaints. Research documenting a free-running rhythm in totally blind participants supports the relationship between drifting circadian phase and recurring sleep symptoms.
A simple example of progressive drift
Imagine that a person's biologically preferred sleep time falls about 30 minutes later each day. After one week the preferred bedtime has moved roughly three and a half hours; after several weeks it may fall in the daytime. This is a hypothetical illustration of a drifting pattern, not a diagnostic threshold or a prediction for an individual. Actual drift rates differ, may be hard to measure from sleep behavior alone, and can be masked when someone forces themselves to keep conventional school or work hours. A specialist distinguishes changes in observable bedtimes from changes in the underlying biological clock.
Why symptoms can disappear and come back
Symptoms may lessen when internal time temporarily aligns with desired nighttime sleep, then recur when it moves away. A person may describe weeks of poor nights followed by an unexpected period of easier sleep. This cycle can lead to misleading interpretations, including that the problem is caused solely by motivation, stress, or inconsistent sleep habits. The recurrent alignment and misalignment are integral to the clinical presentation. A 2025 review of circadian disorders in blindness emphasizes that intervals with few symptoms are entirely compatible with Non-24.
Signs and symptoms of non-24-hour sleep-wake rhythm disorder
The most informative sign is a recognizable long-term timing pattern accompanied by functional impairment. People may find that their natural sleep window shifts steadily later, that bedtime and waking become progressively harder to match with ordinary clock time, and that attempts to maintain a fixed schedule lead to insufficient sleep. Insomnia and excessive sleepiness can alternate; both may be prominent when the body's biological night conflicts with external expectations. The same individual can feel well rested at one phase of the cycle and significantly impaired at another.
Nighttime sleep complaints
At some points in the cycle, a person may lie awake for long periods even after attempting an earlier bedtime. Sleep onset insomnia is common, but difficulty staying asleep or early awakening can also appear when a forced schedule is out of phase with circadian timing. Importantly, a complaint of insomnia describes the experience of inadequate or mistimed sleep; it does not, by itself, prove chronic insomnia disorder. NIH diagnostic guidance recommends considering the timing, duration, and context of the symptoms.
Daytime symptoms and functional effects
When the person's biological night falls during scheduled daytime activities, they may experience strong sleepiness, impaired concentration, slower reactions, irritability, difficulty learning, and trouble attending predictable commitments. Recurrent disruption may create secondary worry about work, academic performance, and relationships. These consequences deserve attention because sleep-wake disorders are assessed partly through their impact on functioning, not only the clock time at which sleep occurs. The NIH description of Non-24 specifically notes alternating daytime sleepiness and episodes with little apparent disturbance.
What symptom-free intervals mean
Some people with Non-24 can sleep reasonably well when allowed to follow their current internal schedule. Others continue to have disrupted sleep because of concurrent conditions, environmental demands, or sleep fragmentation. A few comfortable nights do not negate a convincing long-term drift, just as a single difficult week does not establish it. The diagnostic value lies in the temporal sequence documented across enough days and weeks to identify a repeatable pattern.
Why Non-24 is strongly associated with total blindness
Light is the principal environmental signal that aligns the circadian pacemaker to the solar day. Individuals with no conscious light perception may also lack effective retinal light signaling to the circadian system. When that pathway is absent, the central clock can continue running close to its intrinsic period instead of staying anchored to 24 hours. This explains the particularly high occurrence of Non-24 among people who are totally blind and lack light perception. Published estimates vary by sample and diagnostic method; one specialist review reports estimates around 55%–70% among totally blind individuals, a figure that should not be applied to all visually impaired people.
Visual acuity and circadian photoreception are related but distinct. Some individuals who cannot consciously perceive light still retain physiological responses to light; conversely, others have little or no circadian response. Total blindness, low vision, loss of one eye, and the absence of conscious light perception are not interchangeable clinical categories. The risk of a free-running rhythm depends on the functional light-input pathway and other personal circumstances. Early physiological research of circadian rhythms in totally blind participants showed substantial variation rather than a uniform outcome.
Can someone with normal vision have Non-24?
Yes. Documented sighted cases exist, but they are uncommon and the evidence consists predominantly of case reports and small clinical series. Proposed contributors include unusual circadian period, weak or mistimed light exposure, behavioral and environmental patterns, and complex interactions with other health conditions; assigning one cause to a particular patient requires careful assessment. A published sighted case with actigraphy and melatonin measurements illustrates both the possibility of the diagnosis and the limits of a single case. A 2025 case report likewise describes the clinical challenge of differentiating Non-24 from other timing disorders.
In sighted people, a gradually delayed pattern may be more readily explained by delayed sleep-wake phase disorder, irregular work and sleep schedules, inadequate sleep opportunity, or behavioral factors. Rare diagnoses deserve particularly strong longitudinal evidence. Neither using screens late at night nor identifying as a night owl establishes that the biological clock is truly free-running.
How Non-24 differs from other sleep problems
Non-24 versus delayed sleep-wake phase disorder
Delayed sleep-wake phase disorder usually involves a persistently late but relatively stable sleep window: the person may naturally fall asleep and wake much later than conventional schedules but can maintain that delayed pattern. In Non-24, sleep timing continues to drift through different parts of the day rather than stabilizing at one late phase. Both can impair daytime functioning, and a sighted person's history can sometimes suggest a progression from delay to a more complex pattern. See the separate Delayed Sleep-Wake Phase Disorder guide for the stable-delayed-phase condition.
Non-24 versus irregular sleep-wake rhythm disorder
Irregular sleep-wake rhythm disorder is characterized by a weakly organized daily pattern with multiple sleep episodes dispersed across the day and night. Non-24 usually shows a coherent sleep episode or biological sleep window that shifts progressively relative to the 24-hour clock. A fragmented schedule on an isolated day cannot distinguish the two. Detailed diaries, actigraphy, and clinical history help a clinician establish whether sleep episodes are drifting or genuinely irregular. The AASM clinical guideline treats these as distinct circadian rhythm sleep-wake disorders.
Non-24 versus insomnia disorder
Chronic insomnia disorder centers on persistent difficulty initiating or maintaining sleep despite adequate opportunity, along with distress or daytime impairment. Non-24 can generate severe insomnia complaints, but its central mechanism is circadian misalignment that changes over time. Some people have both conditions. Multicomponent cognitive behavioral therapy for insomnia (CBT-I) is evidence-based for chronic insomnia, but the circadian rhythm itself may require a different treatment plan. Generic sleep hygiene alone does not reliably synchronize a free-running clock. NIH's circadian treatment guidance describes targeted chronobiological interventions.
Non-24 versus shift work, jet lag, and an unconventional schedule
Night shifts and travel across time zones create a mismatch between internal time and external duties that may resemble Non-24 symptoms. Yet shift work disorder and jet lag disorder have specific links to schedules or travel, whereas Non-24 involves a persisting failure of daily entrainment. A freely chosen late bedtime, social jet lag, inconsistent routines, and a flexible remote-work schedule are behavioral or social patterns unless clinical evidence supports a sleep disorder. A clinician reviews occupational hours, time-zone changes, and periods of unrestricted sleep before assigning a diagnosis.
Other conditions that can coexist or imitate the symptoms
Obstructive sleep apnea, restless legs syndrome, central hypersomnolence disorders, medication effects, substance use, chronic pain, mental-health conditions, and insufficient sleep may produce tiredness or broken sleep without a free-running circadian rhythm. Some may coexist with Non-24 and compound daytime impairment. Bipolar-spectrum mood episodes and medication-related changes in sleep need deserve particular attention when there are marked changes in energy, behavior, or judgment. Assessing differential diagnoses requires more than the direction of a wearable trend line. For a symptom-level overview, see Excessive Daytime Sleepiness: Causes, Warning Signs, and Evaluation.
How clinicians diagnose Non-24
Non-24 is a recognized circadian rhythm sleep-wake disorder in the International Classification of Sleep Disorders, third edition, text revision (ICSD-3-TR). A sleep specialist examines the history, whether sleep-wake timing exhibits progressive drift, whether associated insomnia or excessive sleepiness has meaningful consequences, and whether other explanations are more likely. Persistent problems over approximately three months are typical of the diagnostic framework; brief schedule disruption after travel or illness warrants a different interpretation. The central question is whether the underlying circadian system fails to entrain, not whether a person sometimes sleeps late. NIH diagnostic guidance summarizes medical history, sleep records, and objective tools.
Sleep history and longitudinal sleep diary
A detailed history records the onset and course of symptoms, vision and light perception, sleep opportunity, obligations, days off, caffeine and other substances, medications, mental and physical health, and prior treatments. The person may be asked to record bedtime, estimated sleep onset, night awakenings, final awakening, naps, and work or school times in a sleep diary. For suspected Non-24, data across at least two weeks—and often substantially longer—are useful because the repeating drift may be subtle or obscured by imposed schedules. The best recording duration depends on the suspected circadian period and the clarity of the pattern.
Actigraphy: useful evidence with limitations
Clinical actigraphy uses a validated wrist-worn activity monitor to estimate patterns of rest and activity over multiple days. It can help reveal a systematic drift, especially when interpreted alongside a diary and an account of work or caregiving demands. The AASM actigraphy guideline supports actigraphy as part of evaluating circadian rhythm sleep-wake disorders, with recording duration tailored to the clinical question. Actigraphy infers sleep from movement and can misclassify motionless wakefulness or active sleep; it is not a direct measure of the central circadian clock.
Circadian biomarkers and specialist testing
When uncertainty remains, specialist centers may use repeated measures of melatonin-related markers or other physiological rhythms to estimate circadian phase and intrinsic period. Salivary melatonin, urinary 6-sulfatoxymelatonin, or carefully designed temperature measures can help distinguish a true drifting oscillator from changing behavioral schedules. Serial sampling and technical interpretation are important: a single melatonin test does not prove a non-24-hour rhythm. A 2025 clinical review discusses repeated circadian-marker assessment in people with blindness, while a sighted case report shows how biomarkers and actigraphy can complement the history.
Are sleep studies, home tests, or trackers enough?
Overnight polysomnography measures sleep stages, breathing, movements, and related physiology; it may be appropriate to evaluate sleep apnea or other comorbid disorders but usually cannot demonstrate progressive circadian drift from one night alone. Home sleep-apnea testing addresses a different diagnostic question. Consumer sleep trackers can provide a personal record of bedtime and wake time, but their proprietary estimates of sleep stages and internal circadian phase are not diagnostic proof. Present device reports as contextual observations for a clinician, rather than as a positive or negative test for Non-24.
Treatment: what the evidence supports
The main goal is entrainment: bringing the internal circadian rhythm into a stable and clinically workable relationship with a 24-hour day. The most suitable strategy depends on light perception, the measured or inferred circadian phase, medication interactions, symptoms, health conditions, and the practical schedule the person wishes to maintain. Treatment response may require weeks or months of monitoring. A biological rhythm can be well aligned while other sleep complaints remain, so clinicians also reassess comorbid insomnia, sleep apnea, psychological distress, and the impact on everyday functioning. AASM guidance distinguishes recommendations supported by controlled evidence from areas with insufficient research.
Strategically timed melatonin
Melatonin is a biological time signal, and its timing can shift circadian phase. For blind adults with Non-24, the 2015 AASM guideline offers a weak recommendation in favor of strategically timed melatonin over no treatment, based on small trials and overall low-certainty evidence. An early placebo-controlled crossover study reported entrainment in six of seven totally blind participants during melatonin treatment. That result supports a genuine circadian effect, while the very small sample cautions against predicting individual success.
Timing matters at least as much as the label on a supplement. The direction and extent of phase shifting depend on when melatonin is taken relative to the person's internal circadian phase; inappropriate timing can make the target alignment harder to achieve. This is why evidence from studies using particular schedules should not be converted into a universal bedtime instruction. Over-the-counter products also vary in quality, and melatonin can interact with other drugs or conditions. The separate Melatonin and the Body Clock guide explains the broader physiology. NIH's treatment overview addresses supplement quality and safety considerations.
Prescription tasimelteon
Tasimelteon is a melatonin-receptor agonist with U.S. FDA approval for Non-24 in adults. This indication is not restricted by the label to blindness, although pivotal controlled trials enrolled totally blind patients. The medication is a prescription treatment requiring review of interactions, adverse effects, suitability, and clinical follow-up. The current FDA prescribing information distinguishes its Non-24 indication from a separate indication for nighttime sleep disturbances in Smith-Magenis syndrome; the pediatric use described for that syndrome must not be assumed to establish pediatric Non-24 efficacy.
In the randomized SET trial of totally blind adults, measured entrainment at one month occurred in 20% of participants receiving tasimelteon and 3% receiving placebo; the separate RESET randomized-withdrawal trial supported maintenance of entrainment during continued treatment. The trial population was selected for measurable non-24-hour circadian rhythms, and these results do not predict identical benefits for all patients with suspected Non-24. The trials were industry-funded and were not direct comparisons with melatonin. The study methods and outcomes are available in the SET/RESET primary publication.
The FDA label warns about somnolence and drug interactions, including strong CYP1A2 inhibitors and strong CYP3A4 inducers, and reports headache, abnormal dreams, and laboratory liver-enzyme elevations among trial adverse reactions. Choice of treatment should account for the patient's medicines, health history, and access to care. Do not start, stop, or change a prescription regimen on the basis of an educational article. A clinician should also explain that clinical effects may emerge gradually, rather than treating the first few days as a definitive test.
Bright-light exposure and darkness timing
Light can advance or delay the circadian system depending on internal circadian phase and timing of exposure. In sighted people, clinicians may consider precisely timed bright light, planned darkness, and other time cues as part of individualized management. However, controlled treatment evidence specifically for sighted Non-24 remains sparse; the AASM guideline did not issue a treatment recommendation for this population. For people with no functional retinal light response, ordinary bright light is unlikely to provide effective circadian entrainment. Residual physiological light sensitivity and eye health should be evaluated before presuming either benefit or futility. AASM and NIH discuss timing-dependent light interventions and safety.
Light therapy is not a universal morning-lamp prescription. Its circadian effect depends on biological timing, which can differ substantially from wall-clock time in Non-24. Eye disease, photosensitizing medications, migraine, and susceptibility to mood elevation may require modified plans or specialist consultation. Exposure intended to stabilize sleep could produce an unwanted phase shift if applied at the wrong internal time. A detailed separate English Hub article on circadian light therapy is planned, so this page retains the disorder-specific treatment discussion and referral guidance.
Structured routines and behavioral support
Regular timing of activities, meals, social commitments, and opportunities for sleep may support a comprehensive treatment plan and help document progress. For people with profound blindness, these non-light cues may be insufficient by themselves to entrain the internal clock. In the AASM review, evidence was too limited to recommend prescribed sleep-wake scheduling or timed exercise as stand-alone treatments for Non-24. Support for consistent routines should therefore be framed as practical care rather than a proven cure. Occupational accommodations, caregiver communication, and realistic scheduling can reduce the burden while entrainment is being pursued.
What about CBT-I, sleeping pills, stimulants, and chronotherapy?
If someone also has chronic insomnia, CBT-I may help with conditioned arousal and unhelpful sleep-related behaviors. Yet a circadian rhythm that continues to drift needs a specific circadian assessment and may require different interventions. Sleeping pills can change perceived sleepiness without necessarily synchronizing circadian timing, and stimulants cannot reliably establish entrainment. The AASM found inadequate condition-specific evidence to recommend wake-promoting drugs for Non-24. Progressively delaying bedtime around the clock, extreme forced wakefulness, and self-directed sleep restriction can destabilize function and should not be attempted as an improvised treatment. AASM treatment guidance describes these evidence gaps.
How evidence differs between blind and sighted patients
Much of the stronger treatment evidence comes from small melatonin studies and tasimelteon randomized trials in totally blind adults. These findings do not automatically generalize to sighted adults, people with residual light perception, or children. In sighted Non-24, the available literature remains concentrated in case reports and observational experience. A sighted individual described in a primary case report did not entrain after one tested combination of bright light and melatonin; that observation does not demonstrate that these methods fail for everyone. The 2025 case literature underscores why personalized assessment is needed.
An AASM 'no recommendation' designation for some treatments and populations reflects inadequate or missing evidence, not proof that the intervention is harmful or ineffective. Conversely, an FDA-approved indication and statistically significant trial result establish a relevant treatment option, not a guarantee of symptom resolution. Read effect sizes, population criteria, treatment duration, and outcomes together. Long-term maintenance often matters because the underlying tendency toward free-running timing can reappear when successful circadian treatment stops. The randomized-withdrawal findings and 2025 review both highlight this issue.
Living with Non-24: practical care and accommodations
Recording patterns without turning monitoring into a diagnosis
A useful personal record includes dates, attempted bedtimes, approximate sleep and wake times, naps, required commitments, relevant medication times, light exposure circumstances, and daytime impacts. Documenting what happens on free days can help show the difference between a natural tendency and an imposed timetable. A concise timeline of several weeks or months can make a first sleep-medicine consultation more productive. If using a wearable, save the raw timing information alongside your own observations and describe the device model and its limitations.
Making work, education, and caregiving more manageable
When symptoms are substantial, individualized adjustments may help preserve participation: flexible start times, remote attendance where possible, reduced early-morning travel during the most difficult phases, and predictable opportunities to reschedule medical appointments. These are practical accommodations whose availability depends on organizational and legal context; they do not replace clinical treatment. Support should focus on measurable functional needs and privacy rather than requiring an individual to disclose an entire medical history to peers. Families can also benefit from understanding why apparently good weeks may be followed by difficult ones.
Safety during severe sleepiness
Avoid driving, operating machinery, or undertaking other safety-critical tasks when you are markedly sleepy, regardless of the presumed cause. Persistent severe sleepiness, episodes of unintended sleep, or occupational safety incidents warrant prompt clinical review. Snoring with witnessed breathing pauses, sudden muscle weakness triggered by emotion, seizure-like events, or major behavioral changes require assessment for additional conditions. Sudden confusion, loss of consciousness, or an immediately dangerous situation requires urgent local emergency care rather than waiting for a routine circadian appointment. NIH diagnostic guidance describes the importance of evaluating other health causes of sleep difficulties.
When to seek a sleep specialist
Arrange an evaluation when a sleep schedule appears to drift progressively for weeks or months, especially if recurring insomnia and daytime sleepiness impair attendance, work, relationships, or safety. Anyone with no light perception and cyclical sleep complaints deserves consideration of a circadian rhythm disorder, even if earlier consultations focused only on insomnia. Sighted people who suspect Non-24 also benefit from a structured differential evaluation before assuming a rare diagnosis. A clinician with experience in sleep medicine and circadian disorders can decide whether extended actigraphy, biomarkers, medication review, or another type of testing is warranted.
Bring previous sleep studies, an accurate medication and supplement list, details of relevant eye conditions or residual light perception, and any records showing a drift over time. Explain both your actual sleep times and the schedule you are trying to keep. If symptoms affect mental health, include those effects in the assessment: circadian misalignment can coexist with anxiety, depression, or other conditions that deserve their own care. Clinical treatment choices should be individualized, particularly during pregnancy, in pediatric patients, and when other medications or health conditions complicate the picture.
Frequently asked questions
Is Non-24 the same as being a night owl?
No. A night owl usually has a later preference that can remain stable. Non-24 involves ongoing drift relative to the 24-hour clock with clinically meaningful symptoms or impairment. A late bedtime alone is not sufficient evidence of the disorder.
Can Non-24 occur without blindness?
Yes, but it is rare in sighted people. Because other sleep-timing and behavioral explanations are considerably more common, diagnosis generally depends on careful longitudinal documentation and an expert assessment. The published sighted cases illustrate this distinction.
Does blindness always cause Non-24?
No. Blindness describes a range of visual and physiological states, and some totally blind individuals retain light-related circadian responses or entrainment through other mechanisms. Risk is especially high with absent functional light input, but a sleep history and, where appropriate, testing are still needed to establish a specific disorder. Physiological findings document variation among individuals.
How long should I track sleep before an appointment?
Begin a diary now rather than delaying an appointment to reach an arbitrary number of days. Two or more weeks can provide useful initial evidence, while detecting a slowly drifting rhythm may require substantially longer observation or repeated circadian measurements. Your clinician can determine an appropriate recording interval. NIH guidance discusses sleep diaries and clinical testing.
Can a watch or sleep app diagnose Non-24?
No. Consumer devices may help show approximate timing across weeks but cannot independently establish clinical criteria or the biological period. Specialist-grade actigraphy and circadian marker assessment may strengthen a diagnosis when the history suggests a free-running pattern. AASM actigraphy recommendations concern clinical interpretation, not the validity of every consumer tracker.
Will melatonin fix the disorder?
Melatonin can synchronize circadian timing in some totally blind adults, but individual outcomes vary and treatment timing is critical. In sighted patients, controlled evidence remains inadequate for a confident population-level recommendation. Discuss any use with a clinician who understands circadian phase, other medications, and the difference between treating sleepiness and achieving entrainment. AASM reviews the strength of this evidence.
Is tasimelteon approved for children with Non-24?
No pediatric Non-24 indication is established in the U.S. prescribing information reviewed here. The separate pediatric authorization in the FDA label concerns nighttime sleep disturbances associated with Smith-Magenis syndrome and should not be mistaken for evidence of pediatric Non-24 efficacy.
Can I treat Non-24 simply by forcing myself to stay awake?
Forced wakefulness and unsupervised chronotherapy carry risks such as sleep deprivation and impaired vigilance and do not guarantee entrainment. A schedule that looks normal on a calendar may coexist with an internally drifting clock. Treatment planning should follow individual evaluation, particularly when driving, mental health, and occupational safety are affected.
Does this disorder last forever?
Non-24 can be persistent when the underlying source of failed entrainment continues, especially in the absence of effective light input. Some people achieve stable synchronization with carefully selected treatment, and others need sustained follow-up, schedule accommodation, or adjustments to the plan. A response during one period should be assessed over enough time to establish stability. Maintenance results from SET/RESET help explain why ongoing treatment may matter.
Key takeaways
Non-24 is a clinical circadian rhythm sleep-wake disorder defined by progressive drift of internal sleep-wake timing relative to the 24-hour day, with recurring sleep complaints and functional consequences. Total blindness without effective light input substantially increases risk, while sighted cases are rare. A history, longitudinal sleep diary, clinical actigraphy when appropriate, and sometimes specialist circadian biomarkers help distinguish the condition from delayed phase, irregular sleep, chronic insomnia, insufficient sleep, and other disorders. Strategically timed melatonin has a weak AASM recommendation for blind adults; prescription tasimelteon has adult U.S. approval and randomized trial evidence in totally blind adults. Light and behavioral approaches must be individualized, with recognition of limited data in sighted populations. The safest next step for a recurring drifting schedule is a specialist assessment rather than a self-prescribed timing protocol.
Related Articles
Circadian Rhythms: The Body Clock and Sleep Timing — how circadian clocks are aligned with the 24-hour environment.
Delayed Sleep-Wake Phase Disorder: Symptoms and Treatment — how a stable late phase differs from progressive drift.
Melatonin and the Body Clock: Timing, Evidence, and Risks — the physiology, timing and safety of melatonin.
Excessive Daytime Sleepiness: Causes, Warning Signs, and Evaluation — understanding and evaluating a central daytime symptom.
References
Albajar, I., Obach, A., Montini, A., & Muñoz Lopetegi, A. (2025). Non-24-hour sleep-wake rhythm disorder in a sighted patient. Practical Neurology, 25(6), 578–580. DOI: 10.1136/pn-2025-004639.
Auger, R. R., Burgess, H. J., Emens, J. S., Deriy, L. V., Thomas, S. M., & Sharkey, K. M. (2015). Clinical practice guideline for the treatment of intrinsic circadian rhythm sleep-wake disorders. Journal of Clinical Sleep Medicine, 11(10), 1199–1236. Full AASM guideline.
Garbazza, C., Bromundt, V., Eckert, A., Brunner, D. P., Meier, F., Hackethal, S., & Cajochen, C. (2016). Non-24-hour sleep-wake disorder revisited: A case study. Frontiers in Neurology, 7, Article 17. DOI: 10.3389/fneur.2016.00017.
Lockley, S. W., Dressman, M. A., Licamele, L., et al. (2015). Tasimelteon for non-24-hour sleep-wake disorder in totally blind people (SET and RESET): Two multicentre, randomised, double-masked, placebo-controlled phase 3 trials. The Lancet, 386, 1754–1764. DOI: 10.1016/S0140-6736(15)60031-9.
National Heart, Lung, and Blood Institute. (2022a). Circadian rhythm disorders: Diagnosis. NIH clinical information.
National Heart, Lung, and Blood Institute. (2022b). Circadian rhythm disorders: Treatment. NIH clinical information.
National Heart, Lung, and Blood Institute. (2022c). Circadian rhythm disorders: Types. NIH clinical information.
Quera-Salva, M. A., Hartley, S., & Uscamaita, K. (2025). Circadian rhythm disorders in the blind. Handbook of Clinical Neurology, 206, 113–123. PubMed / DOI record.
Sack, R. L., Lewy, A. J., Blood, M. L., Keith, L. D., & Nakagawa, H. (1992). Circadian rhythm abnormalities in totally blind people: Incidence and clinical significance. Journal of Clinical Endocrinology & Metabolism, 75(1), 127–134. DOI: 10.1210/jcem.75.1.1619000.
Sack, R. L., Brandes, R. W., Kendall, A. R., & Lewy, A. J. (2000). Entrainment of free-running circadian rhythms by melatonin in blind people. New England Journal of Medicine, 343, 1070–1077. DOI: 10.1056/NEJM200010123431503.
Smith, M. T., McCrae, C. S., Cheung, J., et al. (2018). Use of actigraphy for the evaluation of sleep disorders and circadian rhythm sleep-wake disorders: An American Academy of Sleep Medicine clinical practice guideline. Journal of Clinical Sleep Medicine, 14(7), 1231–1237. Full AASM guideline.
U.S. Food and Drug Administration. (2024). HETLIOZ (tasimelteon) capsules and HETLIOZ LQ oral suspension: Prescribing information, revised January 2024 (FDA-hosted file). Official prescribing information.