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 drug Rozerem (ramelteon) is a melatonin analogue that selectively binds to the melatonin MT and MT 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 (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 B 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.

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 a.m. and average waking time of about 11:30 a.m., 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. Follow-up showed that 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.

Possible treatments for circadian rhythm sleep disorders include:

- Behavior therapy or advice about sleep hygiene where the patient is told to avoid naps, caffeine, and other stimulants. They are also told to not be in bed for anything besides sleep and sex.

- Dark therapy, for example the use of blue-blocking goggles, is used to block blue- and bluegreen wavelength light from reaching the eye during evening hours so that the production of melatonin is not decreased or eliminated.

- Medications such as melatonin and modafinil (Provigil), or other short term sleep aids or wake-promoting agents can be beneficial; the former is a natural neurohormone responsible partly and in tiny amounts for the human body clock. The melatonin agonist Tasimelteon, trade name Hetlioz, has been approved in the USA solely for the treatment of non-24-hour sleep–wake disorder in totally blind people.

- Sleep phase chronotherapy may progressively advance or delay sleep time.

Among people with healthy circadian clocks, there is a continuum of chronotypes from "larks", "morning people", who prefer to sleep and wake early, to "owls", "evening people" or "night people", who prefer to sleep late at night and wake at late times. Whether they are larks or owls, people with normal circadian systems:

- can wake in time for what they need to do in the morning, and fall asleep at night in time to get enough sleep before having to get up.

- can sleep and wake up at the same time every day, if they want to.

- will, after starting a new routine that requires their getting up earlier than usual, start to fall asleep at night earlier within a few days. For example, someone used to sleeping at 1 a.m. and waking up at 9 a.m. begins a new job on a Monday, and must get up at 6 a.m. to get ready for work. By the following Friday, the person has begun to fall asleep at around 10 p.m., and can wake up at 6 a.m. feeling well-rested. This adaptation to earlier sleep/wake times is known as "advancing the sleep phase." Healthy people can advance their sleep phase by about one hour each day.

Researchers have placed volunteers in caves or special apartments for several weeks without clocks or other time cues. Without time cues, the volunteers tended to go to bed an hour later and to get up about an hour later each day. These experiments appeared to demonstrate that the "free-running" circadian rhythm in humans was about 25 hours long. However, these volunteers were allowed to control artificial lighting and the light in the evening caused a phase delay. More recent research shows that adults of all ages free-run at an average of 24 hours and 11 minutes. To maintain a 24-hour day/night cycle, the biological clock needs regular environmental time cues or zeitgebers, e.g., sunrise, sunset, and daily routine. Time cues keep the normal human circadian clock aligned with the rest of the world.

Benzodiazepines are not recommended for the treatment of PTSD due to a lack of evidence of benefit and risk of worsening PTSD symptoms. Some authors believe that the use of benzodiazepines is contraindicated for acute stress, as this group of drugs promotes dissociation and ulterior revivals. Nevertheless, some use benzodiazepines with caution for short-term anxiety and insomnia. While benzodiazepines can alleviate acute anxiety, there is no consistent evidence that they can stop the development of PTSD and may actually increase the risk of developing PTSD 2–5 times. Additionally, benzodiazepines may reduce the effectiveness of psychotherapeutic interventions, and there is some evidence that benzodiazepines may actually contribute to the development and chronification of PTSD. For those who already have PTSD, benzodiazepines may worsen and prolong the course of illness, by worsening psychotherapy outcomes, and causing or exacerbating aggression, depression (including suicidality), and substance use. Drawbacks include the risk of developing a benzodiazepine dependence, tolerance (i.e., short-term benefits wearing off with time), and withdrawal syndrome; additionally, individuals with PTSD (even those without a history of alcohol or drug misuse) are at an increased risk of abusing benzodiazepines. Due to a number of other treatments with greater efficacy for PTSD and less risks (e.g., prolonged exposure, cognitive processing therapy, eye movement desensitization and reprocessing, cognitive restructuring therapy, trauma-focused cognitive behavioral therapy, brief eclectic psychotherapy, narrative therapy, stress inoculation training, serotonergic antidepressants, adrenergic inhibitors, antipsychotics, and even anticonvulsants), benzodiazepines should be considered relatively contraindicated until all other treatment options are exhausted. For those who argue that benzodiazepines should be used sooner in the most severe cases, the adverse risk of disinhibition (associated with suicidality, aggression and crimes) and clinical risks of delaying or inhibiting definitive efficacious treatments, make other alternative treatments preferable (e.g., inpatient, residential, partial hospitalization, intensive outpatient, dialectic behavior therapy; and other fast-acting sedating medications such as trazodone, mirtazapine, amitripytline, doxepin, prazosin, propranolol, guanfacine, clonidine, quetiapine, olanzapine, valproate, gabapentin).

Selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) may have some benefit for PTSD symptoms. Tricyclic antidepressants are equally effective but are less well tolerated. Evidence provides support for a small or modest improvement with sertraline, fluoxetine, paroxetine, and venlafaxine. Thus, these four medications are considered to be first-line medications for PTSD.

Certain children who are particularly attached to their mother or other family figure due to separation anxiety and/or attachment theory often suffer the onset early, in pre-school, crèche or before school starts.

School phobia is diagnosed primarily through questionnaires and interviews with doctors. Other methods like observation have not proven to be as useful. This is partly because (school) anxiety is an internal phenomenon. An example of a modern multidimensional questionnaire is the "Differential Power Anxiety Inventory 'approach, with twelve scales to diagnose four different areas: anxiety-inducing conditions, manifestations, coping strategies and stabilization forms."

- Cognitive and lifestyle exploration

- 'School Phobia Test' (SAT)

- 'Anxiety questionnaire for students', (AFS)

Approximately 1 to 5% of school-aged children have school refusal, though it is most common in 5- and 6-year olds and in 10- and 11-year olds, it occurs more frequently during major changes in a child’s life, such as entrance to kindergarten, changing from elementary to middle school, or changing from middle to high school. The problem may start following vacations, school holidays, summer vacation, or brief illness, after the child has been home for some time, and usually ends prior to vacations, school holidays, or summer vacation, before the child will be out of school for some time. School refusal can also occur after a stressful event, such as moving to a new house, or the death of a pet or relative.

The rate is similar within both genders, and although it is significantly more prevalent in some urban areas, there are no known socioeconomic differences.