Paxil (paroxetine) is a drug widely prescribed to treat depression. In women fighting breast cancer it is not uncommon to be prescribed Paxil. The newest research should cause health practitioners to give that practice a second thought.

A team of California researchers developed a drug screening method which they applied to 446 commonly prescribed drugs to look for their estrogenic or hormonal impact on the body. Among them is the antidepressant Paxil which has been identified as have a weak estrogenic effect that throws sex hormones out of balance. Sex hormones may promote the growth of tumors in breast tissues in women since the majority of breast cancers are sensitive to estrogen, reports the Los Angeles Times.

That may help put a study from 2010 in perspective. Canadian breast cancer patients on Paxil were more likely to die from the cancer than those not taking Paxil or taking other antidepressants. At the time it was thought that Paxil might bind to the enzyme needed to metabolize tamoxifen, a drug prescribed to prevent recurrence, therefore making it less effective. Now it could be that Paxil’s weak estrogenic effect might be affecting patients with breast cancer tumors sensitive to estrogen.

Paxil has been on the market since 1992. It is an SSRI (selective serotonin reuptake inhibitor) and approximately one quarter of women under treatment for breast cancer are prescribed SSRIs.

The U.S. Food and Drug Administration recently approved a lower dose of Paxil called Brisdelle, prescribed to treat the symptoms of menopause.

Science has already shown that some plastics have an estrogen mimicking effect capable to increasing the risk of breast cancer. Bisphenol A is used on the manufacture of plastics and epoxy resins.

It’s estimated about 70 percent of breast cancers may be sensitive to these estrogen mimickers.

This new screening method from the City of Hope, a research and treatment center in Duarte, California, is published in the journal Toxicological Sciences.

On the other side of the scale, the antifungal medications biconazole and oxyconazole are reported to have anti-estrogenic effects not unlike drugs given to women to prevent breast cancer and its recurrence.