There are conflicing reports out there. Try Google Scholar and Mayo Clinic both. Everyone is different to complicate it more. My experience was horrible for over 10 weeks. This is only me, but I quit 20mg Tamoxifen and will never go back. One thing, several studies say it's for premenopausal women. I'm 86. Why my doctor put me on it is beyond me but after my extreme side effects I changed doctors and my new oncologist is much more open to my questions and my desires.
The half life varies in different studies. But after a month of not taking it my side effects are lighter the last few days now but still there. Scary to think what would have happened if I'd taken it longer because those half-life days continue to add up if you're take it every day. Even if you are lucky and your doctor starts you on 10 mg which my first oncologist would not even consider.