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Study: Paxil Blocks Cancer Drug's Effects

Women who take the antidepressant Paxil while being treated for breast cancer may increase their risks of dying, according to a Canadian researchers.

In a study published Monday in the British Medical Journal, the researchers concluded that Paxil blocks the therapeutic effect s of tamoxifen, commonly used to treat breast cancer.

Conducted between 1993 and 2005 on 2,430 breast cancer patients age 66 or older, the study found that women who took Paxil and tamoxifen together for 25 percent of the treatment time were 25 percent more likely to die of breast cancer. That risk rose to more than 90 percent among those who took the two drugs together for 75 percent of the cancer treatment time.

Researchers, led by Dr. David Juurlink,of the Institute for Clinical Evaluative Sciences and Sunnybrook Health Sciences Center in Toronto, theorize that Paxil, the generic drug paroxetine marked as Paxil by GlaxoSmithKline, interferes with the compound the body uses to process tamoxifen.

They said they found no such link in patients taking other antidepressant medications.

They recommend that physicians treating breast cancer patients prescribe another antidepressant, but they warn against abruptly stopping the use of Paxil.