Women taking a popular anti-depressant at the same time as a drug used to stop breast cancer recurring are more likely to die from the disease, doctors warn.
Researchers have found that the anti-depressant Seroxat can interfere with tamoxifen, which is prescribed to thousands of breast cancer survivors for five years at a time.
The findings have major implications because many of these women also suffer from depression, with up to one in four affected.
Women taking anti-depressant Seroxat at the same time as breast cancer drug tamoxifen are more likely to die from breast cancer, doctors warn
However, other anti-depressants did not have the same effect.
A study led by a team from the Sunnybrook Health Sciences Centre and the University of Toronto in
Canada looked at 2,430 women aged 66 and over who were being treated between 1993 and 2005.
All were taking tamoxifen and one of five anti-depressants, including Seroxat, which was the most commonly prescribed. Seroxat is also known as paroxetine.
Over the next 2.4 years, 374 died from breast cancer. Analysis showed that those taking Seroxat were far more likely to die from breast cancer and slightly more likely to die from any other cause, compared with women not on the drug.
The researchers found that if patients took Seroxat for 25 per cent of the time they were on tamoxifen, they were 24 per cent more likely to die from breast cancer.
When Seroxat was taken for 50 per cent of the time, there was a 54 per cent increase in the chance of death, and when taken for 75 per cent of the treatment patients were 91 per cent more likely to die.
'In conclusion, our findings indicate that the choice of anti-depressant can significantly affect survival in women receiving tamoxifen for breast cancer', their report published in the British Medical Journal said.
But the authors stressed that women should not stop taking tamoxifen and that their study does not imply that Seroxat causes or influences the course of breast cancer.
'This is simply a situation in which [Seroxat] impairs the effectiveness of tamoxifen,' they said.
Dr David Juurlink, one of the study's authors, said: 'When co-prescription of tamoxifen with an anti-depressant is necessary, preference should be given to anti- depressants that exhibit little or no impact on tamoxifen's metabolism.'
Meg McArthur, senior policy and information officer at Breakthrough Breast Cancer, said anyone with concerns should discuss them with their doctor.
A spokesman for GlaxoSmithKline, which makes Seroxat, said the firm was aware of the link and had updated warnings on the label of the drug in 2008.
She added: 'Following publication of this new study, GSK will review these additional data and will work with regulatory authorities to determine next steps
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