Hi! I am on tamoxifen and my oncologist let me reduce my dose to 10 mg and then 5 mg. I take it at night right before bed. Honestly i really do not have any side effects that truly bother me. My periods are a little bit weird and some bladder issues sometimes but other than that I am good. You should at least try it. See if your oncologist will let you reduce your dose if 20 mg is to strong.