I'm prescribed 20mg/day (the max allowed), but suggested initial dose was 20mg twice a week (which is the NICE recommendation), and adjust dose to symptoms.
My liver didn't like tamoxifen very much, and it would eventually have given me non-alcoholic fatty liver disease (about half the women on tamoxifen for 5 years get NAFLD). So I set about minimising my dose. Breasts grow in bursts, so I only took it during a growth bust.
Tamoxifen has a long build-up, about 2 months to get to working level, and 3 months to get to final level. So if you are taking it only when needed, it's going to take a long time to start working, and to counteract breast growth, you don't want that because it works best as soon as possible, and slower the longer the breast growth has been there. I built a mathematical model of the blood concentration based on dosing and data from the manufacturer's tests, and worked out best dosing for me was to take 20mg/day for 8 days to get to final level within 8 days rather than 3 months, and then switch to 2 x 20mg/week, until growth was reversed, and then stop taking it. When I stop, it decays away in 3 months. If I need to start it again before 3 months, I can calculate a reduction in the initial 8 days due to the residual I still have present. This worked well, and my liver enzymes probably only went abnormal for short periods (I only have two liver function samples whilst on tamoxifen, but they fit what I'd expect).
My consultant and GP were happy for me to do this, and it got my liver enzymes back where they should be which pleased my GP, and prevented the moobs which pleased me.
I also talked with a researcher an Mount Vernon hospital who knew about using tamoxifen in men, and she didn't think anyone had tried doing what I was doing before, and jokingly offered me a job!
Since switching from bicalutamide to Zoladex, I haven't needed any tamoxifen. Bicalutamide is the worse HT drug for breast growth, but it can happen with any of them, so I might still need it occasionally on Zoladex.
Some people seem to start on 1 x 20mg/week, and get dose escalated to 2 x 20mg/week or higher if that doesn't work. However, no one seems to think of doing an initial dose escalation when it's given in response to symptoms to get it working faster than in 2 months.
It's reported to work in 70% of men with HT-induced breast growth. I suspect some of the failures are probably down to widespread lack of understanding of the way dosing works and the long rise and decay in blood levels.