@gran71 Ive been on tamoxifen almost 3 years and take losartan for blood pressure.

Info I found on the web, looks like losartan might improve the efficacy of tamoxifen, but a lower dose of losartan might be needed:
“While no direct drug interaction between losartan and tamoxifen has been identified, some research suggests a potential indirect effect. Losartan, an angiotensin II receptor blocker, may help overcome tamoxifen resistance in certain breast cancer cells according to the National Institutes of Health (NIH). This is based on studies showing that losartan can resensitize tamoxifen-resistant cells to tamoxifen treatment. Additionally, tamoxifen may affect the metabolism of losartan by inhibiting CYP2C9 activity, potentially leading to increased losartan levels.”