Postpartum psychosis (PPP), also known as puerperal psychosis or peripartum psychosis, involves the abrupt onset of psychotic symptoms shortly following childbirth, typically within two weeks of delivery but less than 4 weeks postpartum. PPP is a condition currently represented under "Brief Psychotic Disorder" in the Diagnostic and Statistical Manual of Mental Disorders, Volume V (DSM-V). Symptoms may include delusions, hallucinations, disorganized speech (e.g., incoherent speech), and/or abnormal motor behavior (e.g., catatonia). Other symptoms frequently associated with PPP include confusion, disorganized thought, severe difficulty sleeping, variations of mood disorders (including depression, agitation, mania, or a combination of the above), as well as cognitive features such as consciousness that comes and goes (waxing and waning) or disorientation.

The cause of PPP is currently unknown, though growing evidence for the broad category of postpartum psychiatric disorders (e.g., postpartum depression) suggests hormonal and immune changes as potential factors contributing to their onset, as well as genetics and circadian rhythm disruption. There is no agreement in the evidence about risk factors, though a number of studies have suggested that sleep loss, first pregnancies (primiparity), and previous episodes of PPP may play a role. More recent reviews have added to growing evidence that prior psychiatric diagnoses, especially bipolar disorder, in the individual or her family may raise the risk of a new-onset psychosis triggered by childbirth. There are currently no screening or assessment tools available to diagnose PPP; a diagnosis must be made by the attending physician based on the patient's presenting symptoms, guided by diagnostic criteria in the DSM-V (see Diagnosis).

While PPP is seen only in 1 to 2 of every 1000 childbirths, the rapid development of psychotic symptoms, particularly those that include delusions of misidentification or paranoia, raises concerns for the safety of the patient and the infant; thus, PPP is considered a psychiatric emergency, usually requiring urgent hospitalization. Treatment may include medications such as benzodiazepines, lithium, and antipsychotics, as well as procedures such as electroconvulsive therapy (ECT). In some cases where pregnant women have a known history of bipolar disorder or previous episodes of PPP, prophylactic use of medication (especially lithium) either throughout or immediately after delivery has been demonstrated to reduce the incidence of psychotic or bipolar episodes in the postpartum period.

PPP is not an independently recognized diagnosis in the DSM-V; instead, the specifier "with peripartum onset" is used for both "Brief psychotic disorder" and "Unspecified bipolar and related disorders." Recent literature suggests that, more frequently, this syndrome occurs in the context of known or new-onset bipolar illness (see Postpartum Bipolar Disorder). Given the variety of symptoms associated with PPP, a thorough consideration of other psychiatric and non-psychiatric (or organic) causes must be ruled out through a combination of diagnostic labwork and imaging, as well as clinical presentation - a non-exhaustive sample of these other causes is examined below (see Organic postpartum psychoses and Other non-organic postpartum psychoses).

By its diagnostic definition (under the name "brief psychotic disorder with peripartum onset"), PPP occurs either during pregnancy or within 4 weeks after delivery. Generally, PPP symptoms have been observed within 3–10 days of childbirth, though women with a past history of bipolar disorder may experience symptoms even sooner. The persistence of symptoms varies; while the average reported length of an episode may last weeks to several months, there is currently no strong literature documenting the course of individual episodes. Recurrence rates for psychotic episodes, on the other hand, have stronger supporting studies and are covered in more detail below (see Prognosis and Outcomes).

Diagnostic criteria per the DSM-V require the presence of at least one psychotic symptom, defined as delusions, hallucinations, bizarre or incoherent speech (disorganized speech), or abnormal movements (psychomotor behavior) such as catatonia. Delusions, particularly about the infant, are the most commonly reported psychotic symptom associated with PPP. Paranoid delusions are a frequently noted theme in cases of PPP, but a small review noted infrequent cases of delusional misidentification syndromes, such as Capgras syndrome (the belief that someone or something familiar has been replaced with an impostor), Fregoli syndrome (the belief that a stranger is actually a known person in disguise), and others. The latter types of delusions may have a significant negative impact on the bond between a mother and child, raising concerns for the safety of both (see Prognosis and Outcomes).

Both postpartum obsessive-compulsive disorder (OCD) and PPP may present with concerning thoughts about the infant; typically, the thoughts associated with OCD are unwanted and distressing to the individual (who does not wish to act on their thoughts), whereas persons with PPP are often less distressed by their beliefs and may even feel the need to act on them. Compared to schizophrenia, PPP tends to feature less bizarre delusions, and associated hallucinations are more likely to be visual rather than auditory. The sensation of being outside one's body or feeling that one's surroundings are unreal (i.e., derealization) has also been described in cases of PPP. Additional distinctions in PPP compared to classical schizophrenia include the presence of mood and cognitive (or neurological) symptoms.

Rapid mood changes or the presence of unusual moods such as depression or mania (increased energy, decreased need for sleep, etc.) tend to be seen in a large percentage of patients experiencing PPP. Irritability, anxiety, and general difficulties with sleep may also be present. Confusion or disorientation, disorganized thoughts, incoherent speech, or abrupt changes in a person's mental capacity may also be seen in individuals experiencing PPP, though one small study observed these neurological symptoms in only one-quarter of PPP cases. Like delirium, these symptoms may come and go in unpredictable patterns.