fluoxetine + paroxetine + tamoxifen

This represents a potentially problematic drug combination rather than an intentional formulation. Tamoxifen is a selective estrogen receptor modulator (SERM) used in breast cancer treatment that requires metabolism by CYP2D6 to its active form, endoxifen. Fluoxetine and paroxetine are potent CYP2D6 inhibitors that can significantly reduce tamoxifen's effectiveness by preventing this conversion. Clinical studies have shown reduced endoxifen levels when these antidepressants are co-administered with tamoxifen, potentially compromising breast cancer treatment outcomes. Medical guidelines generally recommend avoiding this combination and suggest alternative antidepressants with minimal CYP2D6 inhibition (such as citalopram, escitalopram, sertraline, or venlafaxine) for patients requiring both tamoxifen and antidepressant therapy.