What Do Estrogen Blockers Do?

Updated November 21, 2016

Aromatase inhibitors or oestrogen blockers block the production of oestrogen, which is known to increase the risk of breast cancer. Humans now have higher levels of oestrogen in their bodies than ever before due to environmental toxins, pesticides, plastics and the birth control pill.


Oestrogen blockers are sometimes referred to as anti-oestrogen. Oestrogen blockers lower oestrogen levels in the body and prevent testosterone, which both men and women have, from converting into oestrogen. Oestrogen blockers are sometimes referred to as oestrogen detoxifiers, according to


When oestrogen levels are lowered, testosterone levels will increase. Too much oestrogen can lead to cancer as well as to increased body fat and man breasts, which is medically referred to as gynaecomastia.

Benefits Versus Risks

Oestrogen is a wonderful and vital hormone when a woman is young. It allows her to physically develop and reproduce. Men also need oestrogen, but in a much lower degree than women. However, oestrogen, when it becomes dominant, can result in a bad outcome, namely cancer.

Too Little, Too Much

As we age, our oestrogen levels increase, which reduces sperm count in men and increases the risk of cancer, particularly prostate and cervical cancers. When women go through menopause their oestrogen levels significantly decline, which creates another host of problems because women need oestrogen to stay healthy, just not too much of it. Many post-menopausal women opt to take hormone replacement therapy (HRT) but that has been found to put them at higher risk for breast cancer. It’s a vicious cycle.


Tamoxifen, a drug, was the oestrogen blocker drug of choice for years for post-menopausal women who have breast cancer that is oestrogen-dependent for growth. However, in 1999, Aromasin was approved in the United State for the treatment of post-menopausal women with advanced breast cancer whose tumours were no longer responding to Tamoxifen treatment.


Aromasin is a steroidal aromastase in-activator. This means that it specifically targets and irreversibly binds to the enzyme called aromatase, which is needed to produce oestrogen. When oestrogen stops being produced in the body, breast cancer cells can’t survive.


Examples of oestrogen blockers are formestane, testolactone and vorozole. These are aromatase inhibitors. Selective oestrogen receptor modulates include clomifene, arzooxifene and tamoxifen, which block oestrogen receptors.

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About the Author

Cindi Pearce is a graduate of Ohio University, where she received her bachelor’s degree in journalism. She completed both the undergraduate and graduate courses offered by the Institute of Children’s Literature. Pearce has been writing professionally for over 30 years.