In a new study from Washington University in St. Louis, researchers found that many commonly prescribed older antipsychotic medications, and some newer ones, are associated with a much higher risk of breast cancer.
Antipsychotics are prescribed for a broad range of conditions, including depression, bipolar disorder, schizophrenia, dementia and autism spectrum disorders.
While earlier studies have uncovered links between antipsychotic drug use and breast cancer risk, this is the first study to compare newer antipsychotics to older drugs.
Prolactin is an important hormone involved in puberty, pregnancy and breastfeeding.
However, many antipsychotics elevate prolactin levels and can produce side effects such as menstrual cycle irregularities, abnormal breast milk production and abnormal breast tissue growth.
Many women with psychiatric illnesses such as schizophrenia and bipolar disorder will take antipsychotics for decades, and they are essential to keeping symptoms in check.
But both older antipsychotic medicines and some newer drugs raise levels of prolactin and increase the risk of breast cancer.
The researchers classified antipsychotic drugs into three categories, based on their established effects on prolactin.
Category 1 included drugs associated with high prolactin levels, such as haloperidol, paliperidone and risperidone.
Category 2 drugs, which had mid-range effects on prolactin, included the drugs iloperidone, lurasidone and olanzapine.
Category 3 included drugs with less of an effect on prolactin levels, such as aripiprazole, asenapine, brexpiprazole, cariprazine, clozapine, quetiapine and ziprasidone.
The researchers compared the effects of all three categories of antipsychotic drugs to anticonvulsant drugs and lithium, which also often are prescribed to treat psychiatric disorders.
Of the 540,737 women in the database taking antipsychotics, only 914 were identified as having breast cancer. But a significant number of those women were taking drugs known to increase prolactin.
The relative risk of breast cancer was 62% higher for women who took Category 1 drugs and 54% higher for those taking Category 2 drugs, whereas Category 3 antipsychotics were not linked to an increase in breast cancer risk.
The team says certain drugs are known to elevate prolactin, and the women taking those drugs were more likely to have breast cancer.
In people, prolactin levels tend to be lower in women who have had more children at a younger age than in women who have fewer children or wait until they are older to do so.
For more information about breast cancer and your health, please see recent studies about healthy levels of vitamin D may boost breast cancer outcomes and results showing that this diabetes drug may help treat aggressive breast cancer.
The study is published in the Journal of Clinical Psychopharmacology. One author of the study is Tahir Rahman, MD.
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