Tamoxifen is a prodrug activated to endoxifen via CYP2D6. Paroxetine is a strong CYP2D6 inhibitor: endoxifen falls 65%, antiestrogen effect lost. Cohort studies show increased breast cancer mortality with long-term combination.
Symptoms
Tumour progression on imaging after 6-12 months.
Management
Alternative SSRI – sertraline, escitalopram, citalopram, fluvoxamine (no CYP2D6 inhibition). If refractory depression – oncology + psychiatry discussion.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.