Psychosis is a condition of the mind that results in difficulties determining what is real and what is not real. Symptoms may include delusions and hallucinations, among other features. Additional symptoms are incoherent speech and behavior that is inappropriate for a given situation. There may also be sleep problems, social withdrawal, lack of motivation, and difficulties carrying out daily activities. Psychosis can have serious adverse outcomes.

As with many psychiatric phenomena, psychosis has several different causes. These include mental illness, such as schizophrenia or schizoaffective disorder, bipolar disorder, sensory deprivation and in rare cases, major depression (psychotic depression). Other causes include: trauma, sleep deprivation, some medical conditions, certain medications, and drugs such as cannabis, hallucinogens, and stimulants. One type, known as postpartum psychosis, can occur after giving birth. The neurotransmitter dopamine is believed to play an important role. Acute psychosis is considered primary if it results from a psychiatric condition and secondary if it is caused by a medical condition or drugs. The diagnosis of a mental health condition requires excluding other potential causes. Testing may be done to check for central nervous system diseases, toxins, or other health problems as a cause.

Treatment may include antipsychotic medication, psychotherapy, and social support. Early treatment appears to improve outcomes. Medications appear to have a moderate effect. Outcomes depend on the underlying cause. In the United States about 3% of people develop psychosis at some point in their lives. The condition has been described since at least the 4th century BC by Hippocrates and possibly as early as 1500 BC in the Egyptian Ebers Papyrus.