I have had breast cancer twice. The first one diagnosed in 2000 was hormone-driven and I went on Effexor to control the hot flashes I developed when taking Tamoxifen (binds to estrogen and puts you into a chemically induced menopause). I was only ever on 25mg regular-release Effexor (about 18 years) and would have just stayed on Effexor if I had realized how much effect quitting Effexor would have. Even at a low dose, it has powerful effects on the brain.