One of the most prevalent side effects from taking tamoxifen, the often-prescribed endocrine therapy drug for estrogen-receptor positive breast cancer, is depression. Whether the depression is associated with a cancer diagnosis or from taking tamoxifen (or both) we do not know. We do know that up to 25 percent of breast cancer patients suffer what is termed “clinically significant depression” following diagnosis. 
Depression is not the only side effect of tamoxifen, by any stretch of the imagination, but it is one of the most prevalent and debilitating side effects. Breast cancer patients and survivors on this drug commonly share with me just how debilitating the depression was for them. Many choose to stop taking it because of this. One told me that coming off the drug was like emerging from a long, dark tunnel out into the sunlight.
SSRI Drugs Prescribed For Depression
So what happens when a woman on tamoxifen goes to her doctor and complains of depression? Yes, you guessed it – she gets prescribed another drug, usually in the form of an SSRI antidepressant. That stands for selective serotonin reuptake inhibitor. Without getting too heavily into the chemistry of how these drugs work (which is not my purpose with this article), in a nutshell, they work by increasing serotonin levels in the brain, serotonin being a neurotransmitter (chemical messenger) that carries signals between brain cells. SSRI drugs work by blocking the reabsorption (aka reuptake) of serotonin, thus making serotonin more available for use in the brain. This is supposed to help ease the depression.
Estrogen’s Role in Brain Health
So why does tamoxifen cause depression? It is an estrogen antagonist, meaning it blocks the receptor sites on cells that estrogen would normally take up and direct the action of those cells. The problem with blocking the body’s natural estrogen is that it has a huge role to play in brain health (among many other biological activities). Estrogen has a protective effect on brain neurons and affects the nervous system in many different ways. By blocking estrogen, tamoxifen quite effectively compromises a person’s moods and cognitive health, even normal coordination and movement. It is a known fact that high doses of estrogen exert an anti-depressant effect in humans.
So What’s the Problem with Antidepressants and Tamoxifen Use?
A 2010 study by Canadian researchers, published in the British Medical Journal, had some interesting (and rather worrisome) findings. The researchers were hoping to discover whether using SSRI antidepressants concurrently with tamoxifen reduced the effectiveness of tamoxifen. The study was done with 2,430 women in Ontario, Canada, aged 66 years or older. These women started taking tamoxifen between January 1, 1993 and December 31, 2005.
What they discovered was quite remarkable. For women taking the SSRI drug Paxil (generic name paroxetine – one of the most commonly prescribed drugs for depression) along with tamoxifen, there was a much higher risk of death from breast cancer, namely a 24% – 91% higher risk, depending on length of time the drugs were taken together. The researchers stated that of the women taking tamoxifen and Paxil, 374 (or 15.4%) of them died of breast cancer during follow-up (mean follow-up 2.38 years). They saw no such risk with other anti-depressants, mainly paroxetine/Paxil. Researchers concluded that the use of Paxil during tamoxifen treatment was associated with an increased risk of death from breast cancer, supporting the hypothesis that Paxil can reduce or abolish the benefit of tamoxifen in women with breast cancer. These researchers concluded “We estimate that treatment with paroxetine for 41% of tamoxifen therapy (the median in our study) could result in one additional breast cancer death at five years for every 20 women so treated.”  (bold type added for emphasis)
A newer American study reported in December 2015 in the Journal of the National Cancer Institute found no such increased risk for those taking paroxetine together with tamoxifen. The study followed 16,887 Californian breast cancer survivors diagnosed from 1996 to 2007 and treated with tamoxifen. Of this group of women 8,099 (roughly 50 percent) also took a variety of SSRI antidepressants. 2,946 of the women developed subsequent breast cancer in the 14-year follow-up period. Researchers stated “we did not observe an increased risk of subsequent breast cancer in women who concurrently used tamoxifen and antidepressants, including paroxetine. 
Huh? Of 8,099 survivors, 2,946 develop subsequent breast cancer and there’s no correlation? What the…?
Uninformed medical practitioners continue to prescribe Paxil and other SSRI drugs that are known to inhibit CYP2D6 enzymes (required by the body for the metabolization of tamoxifen). One 2013 study by Dutch researchers stated that “In clinical practice, one should strive to avoid potent CYP2D6 inhibitors as much as possible in tamoxifen-treated patients to reduce the risk of compromising the efficacy of the hormonal therapy.” 
To make matters worse, doctors are prescribing SSRI anti-depressant medications for hot flashes and menopausal symptoms. I was too, but I politely declined my doctor’s offering of this when I was going through terrible hot flashes related to breast cancer treatments. I’m suspicious of these drugs anyway, so that made NO sense to me. Back in 2004 I didn’t even have access to any studies that suggested taking SSRI’s could put me at a higher risk for breast cancer. I just didn’t want these drugs in my body. I also refused tamoxifen due to its long list of side effects and the fact that the State of California and the American Cancer Society have listed it as a carcinogenic agent. Why on earth would we want this in our bodies?
Truthstream Media has an interesting video on this subject on YouTube:
In this video, it is stated that Paxil has a weak estrogenic effect, but enough of an effect to promote breast cancer. Also mentioned is that FORTY to FIFTY PERCENT of American women aged 40-50 are taking these SSRI anti-depressants.
The video also references an older 1999 study entitled Antidepressant Medication Use and Breast Cancer Risk, published in the American Journal of Epidemiology . This study found that taking tricyclic medications (ie SSRI drugs) for more than two years was associated with a two-fold increase in the risk for breast cancer. So we have known since at least 1999 that the use of SSRI drugs could put us at a higher risk for breast cancer.
I just thought you should know about this. As a natural therapist, I wonder about the combined toxicity of tamoxifen and SSRI drugs. Taking these drugs in combination gives the liver a lot of work to do to detoxify them. If the liver is involved in detoxification of these two drugs all the time, that taxes it to an extraordinary degree.
I think there’s a much better way to go. I believe our bodies were uniquely designed to use natural foods, herbs, essential oils and other remedies for our healing. If you’d like to find out more, sign up for my free newsletters over on the right-hand side of this page.
 Breast Cancer Recurrence Risk Related to Concurrent Use of SSRI Antidepressants and Tamoxifen – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2892037/
 Selective Serotonin Reuptake Inhibitors and Breast Cancer Mortality in Women Receiving Tamoxifen: a Population Based Cohort Study – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2817754/
 Tamoxifen and Antidepressant Drug Interaction in a Cohort of 16,887 Breast Cancer Survivors – https://www.ncbi.nlm.nih.gov/pubmed/26631176
 Unjustified Prescribing of CYP2D6 Inhibiting SSRIs in Women Treated with Tamoxifen – http://link.springer.com/article/10.1007/s10549-013-2585-z
 Antidepressant Medication Use and Breast Cancer Risk – http://aje.oxfordjournals.org/content/151/10/951.full.pdf
Estrogen Effects on the Brain: Much More than Sex – http://misc.karger.com/gazette/66/mcewen/art_05.htm
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