Tamoxifen drug–drug interactions (DDI) are controversial, but a careful evaluation of the clinical evidence suggests that CYP2D6 inhibitors and enzyme inducers may reduce tamoxifen efficacy.

The consequences of falsely assuming tamoxifen DDI are important (type I error) are minor, but the consequences of falsely assuming they are not important (type II error) are potentially catastrophic.

Given the ease with which many tamoxifen DDI can be avoided, reason dictates that we act to reduce the risk of tamoxifen DDI.