Endoxifen
tamoxifen metabolite
What it is4-hydroxy-N-desmethyltamoxifen, formed by CYP2D6, roughly a hundred times more potent at the estrogen receptor than tamoxifen.
Why it mattersIt is the species that actually does the work — tamoxifen itself is nearly inactive.
What it changesThis is why CYP2D6 poor metabolizers and strong CYP2D6 inhibitors such as fluoxetine and paroxetine blunt tamoxifen’s benefit.
FDA-approved for
- breast cancer (active metabolite of tamoxifen)
NO BOXED WARNINGS
Principal riskLittle in its own right; see the parent drug