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Side Effects of Clozapine (Clozaril)

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Description: Clozapine (also branded as Clozaril, FazaClo, Versacloz, Clopine, CloZAPine Synthon, Denzapine and Zaponex) is an antipsychotic medication that treats schizophrenia by blocking receptors in the brain for several neurotransmitters (chemicals that nerves use to communicate with each other); these are the same receptors that the brain chemical dopamine acts upon. Schizophrenia is associated with an overactivity of dopamine in the brain and this may be associated with delusions and hallucinations, which are a hallmark of this disease. By blocking the transmission of signals activated by dopamine, the chemistry of the brain is altered, resulting in reduction of symptoms of schizophrenia. Clozapine reduces hallucinations and helps prevent suicide in people who are likely to harm themselves. It helps the patient think more clearly and feel less nervous so that the patient can function in society.

Clozaril Black Box Warning and Serious Side Effects

The FDA issued a Clozaril black box warning for its potential for serious and potentially life-threatening adverse reactions, and thus is normally used for very severe and refractory schizophrenia that does not respond to other pharmacological treatment.(Clozaril drug label as reported by the FDA).


Clozaril has been associated with severe adverse reactions, including convulsions, high white cell count and cardiac rhythm abnormalities. Typically, prescribers monitor white well levels over the course of treatment. This is a trial and error process which can result in you experiencing potentially dangerous adverse effects. Consequently, Clozaril is available only from a certified pharmacy under a special program where the patient agrees to undergo regular blood tests.

Common Side Effects of Clozaril

Common and less serious side effects of clozapine can be bothersome. These include dizziness, weight gain and drowsiness. You may also experience such symptoms as headache, sweating, nausea, vomiting, and diarrhea.In addition, Clozaril very frequently causes a progressive movement disorder known as tardive dyskinesia, which involved involuntary facial movements including grimaces and tongue rolling. Tardive dyskinesia is irreversible. (Clozaril drug label).

Understand Your Risks with the Rxight® Genetic Test

The Rxight® pharmacogenetic testing testing program – which is based on the most comprehensive gene panel available – works by profiling your genetic disposition to adverse drug reactions to clozapine and over 200 different prescription and over-the-counter medications. Clozapine side effects may be minimized by making certain the proper dose is prescribed. The results of Rxight® testing inform your provider how to prescribe clozapine while taking into account your particular genetic makeup, thus laying the groundwork for precise, personalized care.

How Does Pharmacogenetic Testing Work?

Many people have normal activity of the genes which encode for liver enzymes responsible for metabolizing Clozaril, and thus experience therapeutic value with few serious side effects on standard doses. However, some people may have differences in one or more of these liver enzymes, based on their genes, which leads to dangerously high levels, resulting in serious adverse reactions, or medication inefficacy. There are 18 primary genes involved in medication metabolism, and their variants (alleles) are analyzed to determine which variant you have. With the results of Rxight® PGx testing, your prescriber can adjust your dose based on your genetically modulated liver enzyme activity targeting a particular drug or drug class – preferably before treatment begins.

Contributors to this Article: Michael Sapko, MD, Phd and Deborah Kallick, PhD, Medicinal Chemistry

Read more about Rxight® genetic testing for drug metabolism