Adjustment disorders are very common. They are one of the most common diagnoses given in a hospital psychiatric consultation setting, frequently reaching up to 50 percent. About 5 to 20 percent of patients in an outpatient mental health clinic meet the criteria for this diagnosis as well.
Bipolar disorder, acute stress reaction, and substance-induced anxiety disorder are not diagnosed as commonly as adjustment disorder.

Patients with psychiatric conditions may experience a wide variety of abnormalities of thought content, including hallucinations, delusions, illusions, hopelessness, helplessness, depersonalization, and derealization.
* Hallucinations: False sensory perceptions without stimuli present; they can be tactile, olfactory, gustatory, auditory, or visual
* Delusions: False beliefs that are firmly maintained despite contrary evidence
* Illusions: False perceptions of real stimuli
* Hopelessness: A belief that things will not improve
* Helplessness: A belief that one will not be able to change the course of events
* Depersonalization: Feeling far away or disconnected from oneself
* Derealization: A sense that one's environment has changed

Ziprasidone, olanzapine, quetiapine, and risperidone are all atypical antipsychotics. Ziprasidone is the least likely to cause weight gain and has been shown to lower triglyceride levels. For patients at an increased risk for developing metabolic syndrome, ziprasidone is the antipsychotic of choice.

Circadian rhythm sleep-wake disorders are characterized by a mismatch between a person's biological clock and the environment. There are five subtypes:
* Delayed sleep phase type: falling asleep and waking later than desired
* Advanced sleep phase type: falling asleep and waking earlier than desired
* Irregular sleep-wake type: falling asleep and waking at random times
* Non-24-hour sleep-wake type: falling asleep and usually waking progressively later than desired
* Shift work type: sleepiness associated with changes in work schedule
Jet lag refers to feeling sleepy or "hungover" after crossing time zones. It is no longer considered a sleep disorder by the DSM-5.

In schizophrenia, the patient suffers from an increase in dopamine, which can result in psychotic symptoms and other symptoms associated with this illness.
In Parkinson's disease, there is a decrease in dopamine. When a patient is suffering from anhedonia, there is also a decrease in dopamine.
In bipolar affective disorder, there is an increase in glutamate.