A number of new antipsychotic drugs (the so-called "atypical antipsychotics") have been introduced since 1990. The first of these, clozapine (Clozaril), has been shown to be more effective than other antipsychotics, although the possibility of severe side effects ― in particular, a condition called agranulocytosis (loss of the white blood cells that fight infection) ― requires that patients be monitored with blood tests every one or two weeks. After a year of stable white blood cell results, blood monitoring can be dropped down to once a month. Studies show that clozapine may be more effective than other antipsychotics in some people. Newer antipsychotic drugs, such as risperidone (Risperdal), quetiapine (Seroquel), olanzapine (Zyprexa), and Abilify (Aripiprazole) are safer regarding the movement related side effects (known as tardive dyskinesia) common with first-generation antipsychotics, and they do not have the same risk of lowering white blood cell counts like Clozaril, but many of the atypical antipsychotics can contribute to metabolic side effects such as weight gain, increased glucose and lipids.
Olanzapine (Zyprexa) has many similarities to Clozaril: it appears to be similar in effectiveness and reversal of negative symptoms, but free of the risk of agranulocytosis.
Even the older antipsychotic drugs are often very effective in treating certain symptoms of schizophrenia, particularly hallucinations and delusions. Unfortunately, these drugs may not be as helpful with other symptoms, such as reduced motivation and emotional expressiveness. The older antipsychotics (which also went by the name of "neuroleptics") ― medicines like haloperidol (Haldol) or chlorpromazine (Thorazine) ― may even produce side effects that resemble negative symptoms. Often, lowering the dose or switching to a different medicine may reduce these side effects; the newer medicines, including olanzapine (Zyprexa), quetiapine (Seroquel), aripiprazole (Abilify) and risperidone (Risperdal) appear less likely to have this problem. Sometimes when people with schizophrenia become depressed, other symptoms can appear to worsen. The symptoms may improve with the addition of an antidepressant medication.
Source: Multiple sources, including Schizophrenia National Institute of Mental Health, revised 2006.