 As such, it is a selective estrogen receptor modulator (SERM), with predominantly estrogenic effects but also with antiestrogenic effects, and was arguably the first SERM to ever be introduced.CTA can antagonize estradiol at the level of the hypothalamus, resulting in disinhibition of the hypothalamic–pituitary–gonadal axis and an increase in estrogen levels.Clomifene and tamoxifen were both derived from CTA via structural modification, and are much lower-efficacy partial agonists than CTA and hence much more antiestrogenic in comparison.