How long until tamoxifen if effective?

Good question. I'm going to be starting it myself within a week. I would think it depends on whether you are taking it after other treatments and surgery and as a preventative. Then I don't think there is a way to know if it is effective unless you just figure that if you do not have a recurrence that it was effective. Unless if one has a tumor and they give tamoxifen to see if it shrinks, I've read that to notice any changes one would be on it for a few weeks to take affect and hopefully see improvement by scans.

I may be wrong,but that's how I've understood it.