the underlying problem is that the patient cannot sleep when sleep is desired, needed or expected. incorporating minor updates (icsd-3, 2014), the diagnostic criteria for delayed sleep phase disorder are: an intractable delay in the phase of the major sleep period occurs in relation to the desired clock time, as evidenced by a chronic or recurrent (for at least three months) complaint of inability to fall asleep at a desired conventional clock time together with the inability to awaken at a desired and socially acceptable time. when not required to maintain a strict schedule, patients exhibit improved sleep quality and duration for their age and maintain a delayed phase of entrainment to local time. patients have little or no reported difficulty in maintaining sleep once sleep has begun. patients have a relatively severe to absolute inability to advance the sleep phase to earlier hours by enforcing conventional sleep and wake times. sleep–wake logs and/or actigraphy monitoring for at least two weeks document a consistent habitual pattern of sleep onsets, usually later than 2 am, and lengthy sleeps. occasional noncircadian days may occur (i.e., sleep is "skipped" for an entire day and night plus some portion of the following day), followed by a sleep period lasting 12 to 18 hours. the symptoms do not meet the criteria for any other sleep disorder causing inability to initiate sleep or excessive sleepiness. if one of the following laboratory methods is used, it must demonstrate a significant delay in the timing of the habitual sleep period: 1) 24-hour polysomnographic monitoring (or two consecutive nights of polysomnography and an intervening multiple sleep latency test), 2) continuous temperature monitoring showing that the time of the absolute temperature nadir is delayed into the second half of the habitual (delayed) sleep episode. some people with the condition adapt their lives to the delayed sleep phase, avoiding morning business hours as much as possible. the icsd's severity criteria are: mild: two-hour delay (relative to the desired sleep time) associated with little or mild impairment of social or occupational functioning. moderate: three-hour delay associated with moderate impairment. severe: four-hour delay associated with severe impairment. some features of dspd which distinguish it from other sleep disorders are: people with dspd have at least a normal—and often much greater than normal—ability to sleep during the morning, and sometimes in the afternoon as well. in contrast, those with chronic insomnia do not find it much easier to sleep during the morning than at night. people with dspd fall asleep at more or less the same time every night, and sleep comes quite rapidly if the person goes to bed near the time they usually fall asleep. young children with dspd resist going to bed before they are sleepy, but the bedtime struggles disappear if they are allowed to stay up until the time they usually fall asleep. dspd patients usually sleep well and regularly when they can follow their own sleep schedule, e.g., on weekends and during vacations. dspd is a chronic condition. symptoms must have been present for at least three months before a diagnosis of dspd can be made. often people with dspd manage only a few hours sleep per night during the working week, then compensate by sleeping until the afternoon on weekends. sleeping late on weekends, and/or taking long naps during the day, may give people with dspd relief from daytime sleepiness but may also perpetuate the late sleep phase. people with dspd can be called "night owls". they feel most alert and say they function best and are most creative in the evening and at night. people with dspd cannot simply force themselves to sleep early. they may toss and turn for hours in bed, and sometimes not sleep at all, before reporting to work or school. less-extreme and more-flexible night owls are within the normal chronotype spectrum. by the time those who have dspd seek medical help, they usually have tried many times to change their sleeping schedule. failed tactics to sleep at earlier times may include maintaining proper sleep hygiene, relaxation techniques, early bedtimes, hypnosis, alcohol, sleeping pills, dull reading, and home remedies. dspd patients who have tried using sedatives at night often report that the medication makes them feel tired or relaxed, but that it fails to induce sleep. they often have asked family members to help wake them in the morning, or they have used multiple alarm clocks. as the disorder occurs in childhood and is most common in adolescence, it is often the patient's parents who initiate seeking help, after great difficulty waking their child in time for school. the current formal name established in the third edition of the international classification of sleep disorders (icsd-3) is delayed sleep-wake phase disorder. earlier, and still common, names include delayed sleep phase disorder (dspd), delayed sleep phase syndrome (dsps), and circadian rhythm sleep disorder, delayed sleep phase type (dspt). management treatment, a set of management techniques, is specific to dspd. it is different from treatment of insomnia, and recognizes the patients' ability to sleep well on their own schedules, while addressing the timing problem. success, if any, may be partial; for example, a patient who normally awakens at noon may only attain a wake time of 10 or 10:30 with treatment and follow-up. being consistent with the treatment is paramount. before starting dspd treatment, patients are often asked to spend at least a week sleeping regularly, without napping, at the times when the patient is most comfortable. it is important for patients to start treatment well-rested. non-pharmacological one treatment strategy is light therapy (phototherapy), with either a bright white lamp providing 10,000 lux at a specified distance from the eyes or a wearable led device providing 350–550 lux at a shorter distance. sunlight can also be used. the light is typically timed for 30–90 minutes at the patient's usual time of spontaneous awakening, or shortly before (but not long before), which is in accordance with the phase response curve (prc) for light. only experimentation, preferably with specialist help, will show how great an advance is possible and comfortable. for maintenance, some patients must continue the treatment indefinitely; some may reduce the daily treatment to 15 minutes; others may use the lamp, for example, just a few days a week or just every third week. whether the treatment is successful is highly individual. light therapy generally requires adding some extra time to the patient's morning routine. patients with a family history of macular degeneration are advised to consult with an eye doctor. the use of exogenous melatonin administration (see below) in conjunction with light therapy is common. light restriction in the evening, sometimes called darkness therapy or scototherapy, is another treatment strategy. just as bright light upon awakening should advance one's sleep phase, bright light in the evening and night delays it (see the prc). it is suspected that dspd patients may be overly sensitive to evening light. the photopigment of the retinal photosensitive ganglion cells, melanopsin, is excited by light mainly in the blue portion of the visible spectrum (absorption peaks at ~480 nanometers). a formerly popular treatment, phase delay chronotherapy, is intended to reset the circadian clock by manipulating bedtimes. it consists of going to bed two or more hours later each day for several days until the desired bedtime is reached, and it often must be repeated every few weeks or months to maintain results. its safety is uncertain, notably because it has led to the development of non-24-hour sleep-wake rhythm disorder, a much more severe disorder. a modified chronotherapy is called controlled sleep deprivation with phase advance, sdpa. one stays awake one whole night and day, then goes to bed 90 minutes earlier than usual and maintains the new bedtime for a week. this process is repeated weekly until the desired bedtime is reached. earlier exercise and meal times can also help promote earlier sleep times. pharmacological aripiprazole (brand name abilify) is an atypical antipsychotic that has been shown to be effective in treating dspd by advancing sleep onset, sleep midpoint, and sleep offset at relatively low doses. phase response curves for light and for melatonin administration. melatonin taken an hour or so before the usual bedtime may induce sleepiness. taken this late, it does not, of itself, affect circadian rhythms, but a decrease in exposure to light in the evening is helpful in establishing an earlier pattern. in accordance with its phase response curve (prc), a very small dose of melatonin can also, or instead, be taken some hours earlier as an aid to resetting the body clock; it must then be small enough not to induce excessive sleepiness. side effects of melatonin may include sleep disturbance, nightmares, daytime sleepiness, and depression, though the current tendency to use lower doses has decreased such complaints. large doses of melatonin can even be counterproductive: lewy et al. provide support to "the idea that too much melatonin may spill over onto the wrong zone of the melatonin phase-response curve." the long-term effects of melatonin administration have not been examined. in some countries, the hormone is available only by prescription or not at all. in the united states and canada, melatonin is on the shelf of most pharmacies and herbal stores. the prescription medication ramelteon (rozerem) is a melatonin analogue that selectively binds to the melatonin mt1 and mt2 receptors and, hence, has the possibility of being effective in the treatment of dspd. a review by the us department of health and human services found little difference between melatonin and placebo for most primary and secondary sleep disorders. the one exception, where melatonin is effective, is the "circadian abnormality" dspd. another systematic review found inconsistent evidence for the efficacy of melatonin in treating dspd in adults, and noted that it was difficult to draw conclusions about its efficacy because many recent studies on the subject were uncontrolled. modafinil (brand name provigil) is a stimulant approved in the us for treatment of shift-work sleep disorder, which shares some characteristics with dspd. a number of clinicians prescribe it for dspd patients, as it may improve a sleep-deprived patient's ability to function adequately during socially desirable hours. it is generally not recommended to take modafinil after noon; modafinil is a relatively long-acting drug with a half-life of 15 hours, and taking it during the later part of the day can make it harder to fall asleep at bedtime. vitamin b12 was, in the 1990s, suggested as a remedy for dspd, and is still recommended by some sources. several case reports were published. however, a review for the american academy of sleep medicine in 2007 concluded that no benefit was seen from this treatment. prognosis risk of relapse a strict schedule and good sleep hygiene are essential in maintaining any good effects of treatment. with treatment, some people with mild dspd may sleep and function well with an earlier sleep schedule. caffeine and other stimulant drugs to keep a person awake during the day may not be necessary and should be avoided in the afternoon and evening, in accordance with good sleep hygiene. a chief difficulty of treating dspd is in maintaining an earlier schedule after it has been established. inevitable events of normal life, such as staying up late for a celebration or deadline, or having to stay in bed with an illness, tend to reset the sleeping schedule to its intrinsic late times. long-term success rates of treatment have seldom been evaluated. however, experienced clinicians acknowledge that dspd is extremely difficult to treat. one study of 61 dspd patients, with average sleep onset at about 3:00 am and average waking time of about 11:30 am, was followed with questionnaires to the subjects after a year. good effect was seen during the six-week treatment with a large daily dose of melatonin. after ceasing melatonin use over 90% had relapsed to pre-treatment sleeping patterns within the year, 29% reporting that the relapse occurred within one week. the mild cases retained changes significantly longer than the severe cases. adaptation to late sleeping times working the evening or night shift, or working at home, makes dspd less of an obstacle for some. many of these people do not describe their pattern as a "disorder". some dspd individuals nap, even taking 4–5 hours of sleep in the morning and 4–5