Although bipolar and schizophrenia are still, for the most part, thought to be two distinct psychiatric diseases, they are related in many ways. Both diseases usually develop in late adolescence or early adulthood. The genetic causal factors have been found to be highly similar in the two brain diseases; both disorders often appear in the same families. Some people are diagnosed with symptoms of both diseases. Schizophrenia and bipolar, or manic-depressive, disorder also share common symptoms and treatments.
Some medications prescribed for both bipolar and schizophrenia lower levels of protein kinase C (PKC) in the brain. High levels of this brain protein are thought to increase the severity of symptoms related to both diseases such as hearing or seeing things that aren't there, having racing thoughts and experiencing grandiose, or false beliefs, relating to one's personal power. In what is called the dysphoric mood in schizophrenia, schizophrenics often experience severe irritability, anxiety and depression similar to what bipolars, or manic-depressives, tend to have in their depressive periods. If not treated, both bipolars and schizophrenics are extremely likely to abuse drugs or alcohol as a way of "self medicating."
The main difference between the symptoms of schizophrenia and bipolar disorder is mood. Bipolar disease is considered a mood disorder characterized by two extreme moods: manic optimism and depressive hopelessness. The distinct moods are so severe that they interfere with the bipolar's daily life; a mood stabilizer such as lithium is often prescribed. Schizophrenics don't have two separate periods of moods, but rather continually experience different groups of symptoms known as negative and positive; these may be controlled with anti-psychotic medications such as Haldol. Negative symptoms are the most difficult to treat with medication; they show as under-functioning, such as a lack of emotion, speech or expression, while positive schizophrenic symptoms are over-functioning, such as hearing voices or believing in possessing superhuman powers.
It is possible for a person to have both diseases or at least overlapping symptoms. A schizoaffective diagnosis refers to a person with schizophrenia and a mood disorder such as bipolar or major depression. A major depressive disorder differs from bipolar in that it lacks the manic phase. Bipolar and schizophrenia are considered to be especially related. Studies have shown that having schizophrenia makes a person more susceptible to developing bipolar disorder.
Having family members with either schizophrenia or bipolar disorder increases the risk of developing one or both diseases. A family with a history of one disease is likely to have the other disorder as well. Bipolar and schizophrenia have genetic components that are connected with both brain disorders.