Generally, we are told that Tamoxifen does not suppress estrogen. It affects estrogen receptors, not the actual estrogen level in the body.
https://www.webmd.com/breast-cancer/guide/tamoxifen-for-breast-cancer-treatment-and-prevention
Does tamoxifen reduce estrogen?
"It blocks estrogen from working on cancer cells that are sensitive to the hormone. "

Though it's a little more complicated than that:
https://pubmed.ncbi.nlm.nih.gov/7214366/

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