SERM – Selective Estrogen Receptor Modulator


Yep, just reading that gave me a headache. Selective Estrogen Receptor Modulator (SERM) “works by blocking estrogen from attaching to estrogen receptors on these cells.”i Let’s simplify this.


Visualize estrogen as a sort of blobby object. Now imagine a receptor as being a lock on the surface of the estrogen. If that receptor is unlocked the cancer will just waltz right in and raid the refrigerator. Cancer is the worst house guest and will just eat you out of house and home. Now add in a SERM. The SERM is the key to fit in the lock. It locks the estrogen up tight so that when the cancer cell comes to crash the party, it can’t bypass the lock. Without food to sustain it, the cancer cell will wither up and die.


The most common SERM is tamoxifen (which I took for three years). There is also toremifene, but I honestly have not come across anyone who takes this, so I can’t comment from my own knowledge. It should be noted that tamoxifen is the drug of choice if you are pre-menopausal. There are no other options before menopause.


I want to note that a SERM does NOT stop your estrogen production. I find this to be a common misconception. It merely binds with the estrogen so that the cancer cannot feed. For many women, this is a good thing, as estrogen helps keep your bones strong. (there are exceptions to this, so be sure to discuss your bone health with your doctor).


My side effects from tamoxifen included hot flashes, anxiety, bone pain, and insomnia. Some of this I had prior on chemo, so it’s hard to judge individual causes, but I know some of my symptoms got worse after tamoxifen, so it definitely contributed. Side effects vary by person. Others I know had bad joint pain and hair thinning. Some ladies have little in the way of side effects. Most report that the side effects appear after a number of months on the pill. For me, it took about six months before I noticed any real side effects.


Most of what I experienced was manageable. A healthy diet and moderate exercise did much in the way of alleviating pain. Effexor helped with the anxiety and hot flashes. (NOTE: Effexor is the only anti-depressant that does not substantially interact with tamoxifen. Most other antidepressants should be avoided. See drug interactions on a site such as You can also explore full side effect listings on sites such as the Mayo Clinic.iii


One final note on SERMS – one potential side effect is thickening of the uterus lining. I have talked to women who have had issues related to this and have had to undergo biopsies and surgeries. I personally did not experience any issues, however, when I had a hysterectomy, they did find that the lining of my uterus was thickened. So it is something to be aware of, and discussed with your doctor if you have concerns.


If you are menopausal, you also have the option of taking an Aromatase Inhibitor (AI), which is discussed in another section. If you are pre-menopausal and wish to take an AI, you have an extra step to complete first, ovarian suppression.


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