Paxil and Tamoxifen May Cause Breast Cancer Relapse or Death: Study

Canadian researchers are reporting that the antidepressant Paxil may interfere with breast cancer drug treatments, increasing the risk of relapse and death in breast cancer survivors.

The new study, conducted by scientists and doctors at the Institute for Clinical Evaluative Sciences and the Sunnybrook Health Sciences Center in Toronto, was published in the latest issue of the British Medical Journal. Researchers found that selective serotonin reuptake inhibitors (SSRI), like Paxil, can interfere with tamoxifen, an estrogen-based breast cancer therapy drug.

Paxil (paroxetine) is a selective serotonin reuptake inhibitor by GlaxoSmithKline PLC prescribed to treat depression. Approved in 1992, it has become one of the most commonly prescribed drugs in the United States, with sales of just under $1 billion last year. It is also available as a generic.

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Researchers looked at 2430 women age 66 or older who had been treated with tamoxifen for breast cancer between 1993 and 2005, and who were also taking Paxil or another SSRI at some point during that time period. The study’s results indicate that the drug reduces or completely mitigates the effectiveness of tamoxifen, confirming scientists’ suspicions that Paxil inhibits tamoxifen’s bioactivation.

About 1.5 million women worldwide are expected to be diagnosed with breast cancer this year, researchers say. It is the most commonly diagnosed form of cancer for women. Experts estimate that about 25% of women dealing with breast cancer experience a depressive disorder. Many of those women are prescribed an antidepressant.

“Our findings have major implications for clinical practice, particularly in light of the frequency of combination therapy,” researchers said. “In our study, 30% of women who started tamoxifen treatment also received antidepressants, and paroxetine was the most commonly used SSRI.”

The study comes as Glaxo tries to deal with hundreds of lawsuits from plaintiffs claiming that Paxil causes suicidal tendencies and birth defects. The company has reportedly already spent more than half a billion dollars to settle Paxil lawsuits, and still faces hundreds more.

There are currently about 600 more Paxil birth defects lawsuits pending. Following a jury award in October for $2.5 million in one Paxil birth defect trial in Pennsylvania, Savvas Neophytou, a London-based Panmure Gordon analysts, told investors that Glaxo faced a potential liability of $1.5 billion in the cases.

9 Comments

  • SandiDecember 19, 2011 at 9:02 am

    I was diagnosed with inflamitory breast cancer three weeks after my 50 birthday After major chemo , a radical masectomy, all the lymphnodes removed and 35 radiation treatments Iam so thankful I refused any medication for depression . I had many days of crying but I told the Drs No medication unless it is essential.

  • donitaMay 6, 2011 at 4:26 pm

    i had breast cancer back in 2008 started tamoxifen then now i have all knids of major medical going on i have mounting medical bills and because i am homeless living in a motel no insurance i have to look for chairities to help pya medical and now i need major sugory thanks to tamoxifen and i use computer at libary because a poor homeless person can't afford much and no lawyer will let me in there[Show More]i had breast cancer back in 2008 started tamoxifen then now i have all knids of major medical going on i have mounting medical bills and because i am homeless living in a motel no insurance i have to look for chairities to help pya medical and now i need major sugory thanks to tamoxifen and i use computer at libary because a poor homeless person can't afford much and no lawyer will let me in there lawsuits but i have major side effects from tamoxifen if i had insurance and a house i would be in the middle maybe lawyers need to look at the real people who are effected like

  • LoriJune 19, 2010 at 4:16 pm

    I was diagnosed with inflammatory breast cancer 2005. I went through many months of chemo, radiation and surgery. I was prescibed zoloft for depression which I now understand could have conradicted the tamoxifien I have been on for over 3 years. I was switched to cymbalta and then prescribed wlbutrin. Today i found out that all of those drugs would contradict the tamoxifien. IBC is a very aggressi[Show More]I was diagnosed with inflammatory breast cancer 2005. I went through many months of chemo, radiation and surgery. I was prescibed zoloft for depression which I now understand could have conradicted the tamoxifien I have been on for over 3 years. I was switched to cymbalta and then prescribed wlbutrin. Today i found out that all of those drugs would contradict the tamoxifien. IBC is a very aggressive cancer and now i am worried I have not had any helpful effects of the tamoxifien for all these years.

  • SheilaJune 7, 2010 at 3:46 am

    I was on Paxil simply because my doctor thought an antidepressant would help with my lack of energy and sleepiness. I took it for over a year in my early twenties. I was diagnosed with breast cancer at the age of 31! I have been in remission for 2 1/2 years but going through the treatments was a horrifying experence for me and my family! The Paxil didn't improve my energy levels at all. Even [Show More]I was on Paxil simply because my doctor thought an antidepressant would help with my lack of energy and sleepiness. I took it for over a year in my early twenties. I was diagnosed with breast cancer at the age of 31! I have been in remission for 2 1/2 years but going through the treatments was a horrifying experence for me and my family! The Paxil didn't improve my energy levels at all. Even it had I still would rather have been tired than loose half my left breast!

  • MelissaApril 7, 2010 at 5:48 pm

    My mom was diagnosed with breast cancer in 1994 at the age of 46. At which time she had a masectomy and was placed on the drugs Paxil and Tamoxifen. Six years later without warning her breast cancer returned and she died 8 weeks after the recurrance at the age of 51. Now I reading all of this informtion regarding these drugs being a deadly mix and I am just beside myself. Something has to be do[Show More]My mom was diagnosed with breast cancer in 1994 at the age of 46. At which time she had a masectomy and was placed on the drugs Paxil and Tamoxifen. Six years later without warning her breast cancer returned and she died 8 weeks after the recurrance at the age of 51. Now I reading all of this informtion regarding these drugs being a deadly mix and I am just beside myself. Something has to be done about this because my mom did not deserve to die at 51. I am devastated and somethimes cannot get out of bed..I am in therapy.

  • BettyApril 5, 2010 at 2:35 am

    I took Paxil after my husband was killed in a car wreck. 3 years later I had breast cancer. I saw on TV today about a class action law suit.

  • BrendaMarch 29, 2010 at 2:32 pm

    I took paxil...I was terrible experience...My head ached....I got really depressed, nothing was right....I didnt want to life anymore...So doctor said I would get use to it...well I didnt...My husband couldnt go to work and I didnt want him too!!!!!! I was definitely suidicial.... Finally I went back to the doctor (crying) Telling him paxil medicine is the devil himself!!!!!! So the doctor put m[Show More]I took paxil...I was terrible experience...My head ached....I got really depressed, nothing was right....I didnt want to life anymore...So doctor said I would get use to it...well I didnt...My husband couldnt go to work and I didnt want him too!!!!!! I was definitely suidicial.... Finally I went back to the doctor (crying) Telling him paxil medicine is the devil himself!!!!!! So the doctor put me on Effexor.... I got breast cancer August 2009, surgery in September...put on Tamoxfin....radiation 21 treatments!!!!!! Now I'm worried....and really dont know what to do!!!!!! Will this come back?

  • PATRICIAMarch 2, 2010 at 7:18 pm

    My mother inlaw LINDA has been on both paxil and tamoxifen, and is now laying in a hospital bed, hospice has been called in. the breast cancer we thought was gone, it is now metastatic bone cancer. she has maybe a few months left, cant walk, has a rod in her upper arm because her cancer in the bones caused her to loose part of her arm. we are now fighting ssi and disibility. i hope something can [Show More]My mother inlaw LINDA has been on both paxil and tamoxifen, and is now laying in a hospital bed, hospice has been called in. the breast cancer we thought was gone, it is now metastatic bone cancer. she has maybe a few months left, cant walk, has a rod in her upper arm because her cancer in the bones caused her to loose part of her arm. we are now fighting ssi and disibility. i hope something can be done.

  • RENEEFebruary 25, 2010 at 3:43 pm

    My Mother was diagnosed w/ breast cancer in 2001. (she was taking Paxil) she had surgery and the cancer was 'gone'. The cancer returned in 2007 (still taking Paxil) she was using Tamoxfin as part of her treatment. She passed away Aug. 2, 2008. We have recently read the findings that taking Tamoxfin and Paxil are a deadly mix.

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