Clozapine was the first antipsychotic drug to be considered “atypical”.  Three drugs have been developed and released in the U.S.  since clozapine appeared. These  drugs are  risperidone (Risperdal®),  olanzapine (Zyprexa®)  and  quetiapine (Seroquel®).   Several other atypical drugs are currently being tested before they can be released to the market . Researchers   realized that several pharmacologic and clinical properties of these drugs  differ  from those of  previously developed antipsychotics (Perry 2001).
 

How are Atypical Antipsychotics Different from Typical Ones?

Pharmacological Differences:

         Like typical antipsychotics,  Clozapine works by blocking the dopamine D2 receptors.   But this is not the only effect of clozapine in the brain.   This drug also blocks the receptors of another very important neurotransmitter: serotonin.   Because they  decrease the activity of these two chemicals in the brain, atypical drugs are known as a serotonin-dopamine antagonists  (SDA) (Perry 2001)
 ( read about dopamine and serotonin in the neurotransmitters section)

Clinical Differences:

(1)  Drug -induced involuntary muscle contractions (known as  Extrapyramidal Side Effects), which  are very common side effects  among pateints  on typical drugs, are almost never  developed by patients on clozapine or other atypical drugs ( read more about extrapyramidal side effects )
(2)  Clozapine causes none or minimal tardive dyskinesia (TD)   ( read more about tardive dyskinesia )
(3) Patients treated with clozapine are seldom found to have an increase in prolactin levels. Prolactin is a hormone that causes galactorrhea, amenorrhea, and gynecomastia when present in higher than normal levels   (Stahl 2000, in   Perry 2001).
(4) Clozapine appears to effectively diminish negative symptoms, which are usually do not diminished by typical  drugs.
(5)  It seems to be the case that clozapine also has a beneficial effect on patients who have been diagnosed as treatment-refractory (Stahl 1999, in Perry 2001).

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