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Side Effects of Iloperidone (Fanapt)


Side Effects of Iloperidone (Fanapt)

Iloperidone, available under the brand Fanapt, is an atypical antipsychotic drug that is approved to treat schizophrenia. Atypical antipsychotic drugs are also known as second-generation antipsychotics. Like first generation antipsychotics, second generation antipsychotics affect the dopamine neurotransmitter system. Unlike first generation antipsychotics, however, the newer medications also affect other types of receptors and neurotransmitter systems including norepinephrine and serotonin.

Serious Side Effects

Atypical antipsychotics may cause blood dyscrasias, which is an abnormally low level of blood cells (mostly white blood cells). This Fanapt adverse effect is potentially deadly. Patients may be required to have frequent blood tests to monitor for leukopenia, neutropenia and agranulocytosis. Fanapt may cause cardiac rhythm abnormalities, specifically prolongation of the QT interval. The antipsychotic also lowers the seizure threshold, which may be a concern in people with epilepsy or who are prone to having seizures. People with diabetes and pre-diabetes may experiences changes in blood sugar levels while on Fanapt (Fanapt label as published by the FDA).

Common Side Effects

The FDA outlines that the common Fanapt side effects are a rapid heart rate, dizziness, drowsiness, and weight gain.


Slightly less common Fanapt side effects (occurring in 1% to 10% of patients) include:


  • Blurred vision
  • Diarrhea
  • Elevated cholesterol and triglycerides
  • Fatigue
  • Hypotension (low blood pressure)
  • Joint pain
  • Muscle pain
  • Muscle rigidity
  • Muscle spasm
  • Nasal congestion
  • Nausea
  • Palpitations
  • Sexual dysfunction
  • Urinary problems
  • Shortness of breath
  • Skin rash
  • Tremors
  • Xerostomia (severe dry mouth)

Causes of Side Effects

Many Fanapt side effects are caused by the drug’s action on dopamine receptors, the FDA reports. For example, one of the most common Fanapt side effects is elevated serum prolactin level, which occurs in approximately one in four people who take the drug. Elevated prolactin is directly related to alerted dopamine function in the hypothalamus and pituitary glands.


One of the benefits of atypical antipsychotics is that they are less likely to cause extrapyramidal side effects. However, atypical antipsychotics still do cause these issues. Extrapyramidal side effects, and other movement-related Fanapt adverse effects are related to blockade (antagonism) of dopamine receptors. Extrapyramidal side effects are symtopms such as acute dystonia (twisting repetitive movements or abnormal posture), akathisia (inner restlessness or feeling the urge to move), and Parkinsonism (tremors, movement, and stiffness). Tardive dyskinesia (repetitive and involuntary movements) may also occur.

About Pharmacogenetic Testing

Fanapt is broken down by two liver enzymes: CYP2D6 and CYP3A4. CYP2D6 is the major enzyme while CYP3A4 plays a minor role. People who are slow or poor metabolizers in either or both of these cytochrome P450 enzymes may experience unexpected elevations in Fanapt. Higher-than-expected drug levels may cause various Fanapt adverse effects.


People who are poor CYP2D6 and CYP3A4 metabolizers may not have any symptoms until they take a drug or drugs that are broken down by these enzymes. However, by that time, Fanapt side effects may already be present (and in the case of extrapyramidal side effects, permanent). Fortunately, pharmacogenetic testing is now available to detect these liver enzyme variations prior to therapy or before Fanapt adverse effects begin.

Know Your Risk with the Genetic Rxight Test

Rxight® identifies 18 genes on 60 alleles to see how your genes react to over 200 prescription and over-the-counter (OTC) medications. Rxight® works by identifying polymorphisms and assisting your healthcare providers to create an individualized treatment based on your genetic profile. Rxight offers a full range of pharmacogenetic testing panels including CYP2D6 and CYP3A4. If you are concerned about Fanapt side effects, Rxight® pharmacogenetic testing may be able to provide important information for you and your doctor.


For more information on Rxight® call us at 1-888-888-1932 or email us at support@Rxight.com.


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

Read more about Rxight® : What is Pharmacogenetics?